Import Ghostscript 9.56.0ghostscript-9.56

Signed-off-by: Sam James <sam@gentoo.org>

46 files changed, 2079 insertions, 239 deletions

diff --git a/demos/MATLAB/ghostpdl.m b/demos/MATLAB/ghostpdl.m
new file mode 100644
index 00000000..833cf1fd
--- /dev/null
+++ b/demos/MATLAB/ghostpdl.m
@@ -0,0 +1,85 @@
+% Copyright (C) 2001-2022 Artifex Software, Inc.
+%   All Rights Reserved.
+%
+%   This software is provided AS-IS with no warranty, either express or
+%   implied.
+%
+%   This software is distributed under license and may not be copied,
+%   modified or distributed except as expressly authorized under the terms
+%   of the license contained in the file LICENSE in this distribution.
+%
+%   Refer to licensing information at http://www.artifex.com or contact
+%   Artifex Software, Inc.,  1305 Grant Avenue - Suite 200, Novato,
+%   CA 94945, U.S.A., +1(415)492-9861, for further information.
+%
+%
+% Paths in this example are relative to the MATLAB
+% folder in the ghostscript project.  MATLAB only
+% runs on Windows 64 bit machines. Interface is
+% limited to a subset of the API methods due to
+% the fact that the MATLAB API does not allow
+% function pointers.  We want to use the display
+% device callbacks to get the image data created
+% from Ghostscript.  To do this, we have to wrap the
+% callback set up and associated functions into a
+% MEX-file that will serve as an interface between MATLAB
+% and the Ghostscript DLL. We use the C MEX API (as opposed to
+% the C++ MEX API).  The mex file is gs_displaydevice.c
+
+% The creation of the mex file for the display device handling only
+% needs to be done once. Note the use of -R2018a as we are using
+% type-safe data access in the mex file. This also is doing a debug version -g.
+mex 'gs_displaydevice.c' -R2018a -g '../../debugbin/gpdldll64.lib'
+
+% You have to load the library to get the mex file to find the library and
+% to make direct calls to gpdldll64 directly from MATLAB
+if not(libisloaded('gpdldll64'))
+    [nf,warn] = loadlibrary('../../debugbin/gpdldll64.dll','../../pcl/pl/plapi.h')
+end
+
+% Show us the various methods in the DLL
+% libfunctions('gpdldll64')
+
+% Use planar format for MATLAB. See gdevdsp.h for what these bits mean.
+PlanarGray = 0x800802;
+PlanarRGB = 0x800804;
+PlanarCMYK = 0x800808;
+PlanarSpots = 0x880800;
+
+% Let try the display device and return the image
+page_number = 1;
+resolution = 200;
+input_file = '../../examples/tiger.eps';
+tiger_image_rgb = gs_displaydevice(input_file, PlanarRGB, page_number, resolution);
+figure(1);
+imshow(tiger_image_rgb);
+title('RGB rendering');
+
+tiger_image_gray = gs_displaydevice(input_file, PlanarGray, page_number, resolution);
+figure(2);
+imshow(tiger_image_gray);
+title('Gray rendering');
+
+% MATLAB will not display CMYK or NColor Images.  We have to show
+% the separations for this case
+tiger_image_cmyk = gs_displaydevice(input_file, PlanarCMYK, page_number, resolution);
+for k=1:4
+    eval(sprintf('figure(2+k);'));
+    imshow(tiger_image_cmyk(:,:,k));
+    switch k
+        case 1
+            title('Cyan Separation');
+        case 2
+            title('Magenta Separation');
+        case 3
+            title('Yellow Separation');
+        case 4
+            title('Black Separation');
+    end
+end
+
+% At this stage, you can push the image data through MATLAB's ocr if you
+% have the Computer Vision Toolbox and want to do some sort of text
+% analysis.  You can also use direct calls into gpdldll64.  See the
+% C-API demo for examples on what can be done to render to file output or
+% save as PDF, PS, etc.
\ No newline at end of file
diff --git a/demos/MATLAB/gs_displaydevice.c b/demos/MATLAB/gs_displaydevice.c
new file mode 100644
index 00000000..cb12c983
--- /dev/null
+++ b/demos/MATLAB/gs_displaydevice.c
@@ -0,0 +1,514 @@
+/* Copyright (C) 2001-2022 Artifex Software, Inc.
+   All Rights Reserved.
+
+   This software is provided AS-IS with no warranty, either express or
+   implied.
+
+   This software is distributed under license and may not be copied,
+   modified or distributed except as expressly authorized under the terms
+   of the license contained in the file LICENSE in this distribution.
+
+   Refer to licensing information at http://www.artifex.com or contact
+   Artifex Software, Inc.,  1305 Grant Avenue - Suite 200, Novato,
+   CA 94945, U.S.A., +1(415)492-9861, for further information.
+*/
+
+#include "mex.h"
+#include <memory.h>
+#include <assert.h>
+
+#ifndef GHOSTPDL
+#define GHOSTPDL 1
+#endif
+
+#if GHOSTPDL
+#include "../../pcl/pl/plapi.h"   /* GSAPI - gpdf version */
+#else
+#include "psi/iapi.h"       /* GSAPI - ghostscript version */
+#endif
+#include "../../devices/gdevdsp.h"
+/*--------------------------------------------------------------------*/
+/* Much of this set-up is stolen from the C-API demo code */
+
+#ifdef HIDE_POINTERS
+void *hide_pointer(void *p)
+{
+    return (p == NULL) ? NULL : (void *)1;
+}
+
+#define PTR(p) hide_pointer(p)
+
+#else
+
+#define PTR(p) p
+
+#endif
+
+#define PlanarGray 0x800802
+#define PlanarRGB 0x800804
+#define PlanarCMYK 0x800808
+#define PlanarSpots 0x880800
+#define INSTANCE_HANDLE ((void *)1234)
+#define SANITY_CHECK_VALUE 0x12345678
+
+#define SANITY_CHECK(ts) assert(ts->sanity_check_value == SANITY_CHECK_VALUE)
+
+/* All the state for a given test is contained within the following
+ * structure. */
+typedef struct {
+    /* This value should always be set to SANITY_CHECK_VALUE. It
+     * allows us to check we have a valid (or at least plausible)
+     * teststate_t pointer by checking its value. */
+    int sanity_check_value;
+
+    int w;
+    int h;
+    int r;
+    int pr;
+    int format;
+
+    int n;
+    void *mem;
+
+    mxArray **mex_image_data;
+
+} teststate_t;
+
+
+static int
+open(void *handle, void *device)
+{
+    teststate_t *ts = (teststate_t *)handle;
+
+    SANITY_CHECK(ts);
+    mexPrintf("open from C-Mex function\n");
+
+    return 0;
+}
+
+static int
+preclose(void *handle, void *device)
+{
+    teststate_t *ts = (teststate_t *)handle;
+
+    SANITY_CHECK(ts);
+    mexPrintf("preclose from C-Mex function\n");
+
+    return 0;
+}
+
+static int
+close(void *handle, void *device)
+{
+    teststate_t *ts = (teststate_t *)handle;
+
+    SANITY_CHECK(ts);
+    mexPrintf("close from C-Mex function\n");
+
+    return 0;
+}
+
+static int
+presize(void *handle, void *device,
+        int width, int height, int raster, unsigned int format)
+{
+    teststate_t *ts = (teststate_t *)handle;
+
+    SANITY_CHECK(ts);
+    mexPrintf("presize: w=%d h=%d r=%d f=%x\n",
+           width, height, raster, format);
+
+    ts->w = width;
+    ts->h = height;
+    ts->r = raster;
+    ts->format = format;
+
+    if (ts->format & DISPLAY_COLORS_GRAY)
+        ts->n = 1;
+    if (ts->format & DISPLAY_COLORS_RGB)
+        ts->n = 3;
+    if (ts->format & DISPLAY_COLORS_CMYK)
+        ts->n = 4;
+    if (ts->format & DISPLAY_COLORS_SEPARATION)
+        ts->n = 0;
+    if ((ts->format & DISPLAY_DEPTH_MASK) != DISPLAY_DEPTH_8)
+        return -1; /* Haven't written code for that! */
+
+    return 0;
+}
+
+static int
+size(void *handle, void *device, int width, int height,
+     int raster, unsigned int format, unsigned char *pimage)
+{
+    teststate_t *ts = (teststate_t *)handle;
+
+    SANITY_CHECK(ts);
+    mexPrintf("size: w=%d h=%d r=%d f=%x m=%p\n",
+           width, height, raster, format, PTR(pimage));
+
+    ts->w = width;
+    ts->h = height;
+    ts->r = raster;
+    ts->format = format;
+    ts->mem = pimage;
+
+    if (ts->format & DISPLAY_PLANAR)
+        ts->pr = ts->r * height;
+    /* When running with spots, n is not known yet. */
+    if (ts->n != 0 && ts->format & DISPLAY_PLANAR_INTERLEAVED)
+        ts->pr = ts->r / ts->n;
+
+    return 0;
+}
+
+static int
+sync(void *handle, void *device)
+{
+    teststate_t *ts = (teststate_t *)handle;
+
+    SANITY_CHECK(ts);
+
+    mexPrintf("sync\n");
+
+    return 0;
+}
+
+static int
+page(void *handle, void *device, int copies, int flush)
+{
+    teststate_t *ts = (teststate_t *)handle;
+    mwSize dims[3];
+    int num_planes;
+    int i,j,k;
+    unsigned char *des_ptr, *src_ptr, *matlab_ptr, *row_ptr;
+    size_t matlab_planar_raster;
+
+    SANITY_CHECK(ts);
+
+    mexPrintf("page: c=%d f=%d\n", copies, flush);
+
+    /* Transfer to the mex output variables at this time */
+    switch (ts->format) {
+    case PlanarGray:
+        num_planes = 1;
+        break;
+    case PlanarRGB:
+        num_planes = 3;
+        break;
+    case PlanarCMYK:
+        num_planes = 4;
+        break;
+    case PlanarSpots:
+        num_planes = 4;
+        break;
+    }
+
+    /* Matlab uses a column ordered layout for its storage of
+       arrays. So we need to do a little effort here. */
+    /* Allocate MATLAB outputs */
+    dims[0] = ts->h;
+    dims[1] = ts->w;
+    dims[2] = num_planes;
+    *(ts->mex_image_data) = mxCreateNumericArray(3, dims, mxUINT8_CLASS, mxREAL);
+
+    /* Grab image pointer */
+    matlab_ptr = (unsigned char*) mxGetUint8s(*(ts->mex_image_data));
+    matlab_planar_raster = ts->w * ts->h;
+
+    /* Copy to MATLAB memory */
+    for (k = 0; k < num_planes; k++) {
+        des_ptr = matlab_ptr +  k * matlab_planar_raster;
+        src_ptr = (unsigned char*) ts->mem + k * ts->pr;
+        row_ptr = src_ptr;
+        for (i = 0; i < ts->h; i++) {
+            for (j = 0; j < ts->w; j++) {
+                des_ptr[i + j * ts->h] = *row_ptr++;
+            }
+            row_ptr = src_ptr + i * ts->r;
+        }
+    }
+    return 0;
+}
+
+static int
+update(void *handle, void *device, int x, int y, int w, int h)
+{
+    teststate_t *ts = (teststate_t *)handle;
+
+    SANITY_CHECK(ts);
+    /* This print statement just makes too much noise :) */
+    /* mexPrintf("update: x=%d y=%d w=%d h=%d\n", x, y, w, h); */
+
+    return 0;
+}
+
+static void *
+memalloc(void *handle, void *device, size_t size)
+{
+    void *ret = NULL;
+    teststate_t *ts = (teststate_t *)handle;
+
+    SANITY_CHECK(ts);
+
+    ret = malloc(size);
+
+    return ret;
+}
+
+static int
+memfree(void *handle, void *device, void *mem)
+{
+    teststate_t *ts = (teststate_t *)handle;
+
+    SANITY_CHECK(ts);
+    mexPrintf("memfree: %p\n", PTR(mem));
+
+    free(mem);
+
+    return 0;
+}
+
+static int
+separation(void *handle, void *device,
+           int component, const char *component_name,
+           unsigned short c, unsigned short m,
+           unsigned short y, unsigned short k)
+{
+    teststate_t *ts = (teststate_t *)handle;
+
+    SANITY_CHECK(ts);
+
+    mexPrintf("separation: %d %s (%x,%x,%x,%x)\n",
+           component, component_name ? component_name : "<NULL>",
+           c, m, y, k);
+    ts->n++;
+
+    /* Update the plane_raster as n has changed. */
+    if (ts->format & DISPLAY_PLANAR_INTERLEAVED)
+        ts->pr = ts->r / ts->n;
+
+    return 0;
+}
+
+static int
+adjust_band_height(void *handle, void *device, int bandheight)
+{
+    teststate_t *ts = (teststate_t *)handle;
+
+    SANITY_CHECK(ts);
+    mexPrintf("adjust_band_height: Unsupported!");
+
+    return 0;
+}
+
+static int
+rectangle_request(void *handle, void *device,
+                  void **memory, int *ox, int *oy,
+                  int *raster, int *plane_raster,
+                  int *x, int *y, int *w, int *h)
+{
+    teststate_t *ts = (teststate_t *)handle;
+
+    SANITY_CHECK(ts);
+
+    mexPrintf("rectangle_request: Unsupported!");
+    return 0;
+}
+
+/*--------------------------------------------------------------------*/
+/* All those callback functions live in a display_callback structure
+ * that we return to the main code. This can be done using the modern
+ * "callout" method, or by using the legacy (deprecated) direct
+ * registration method. We strongly prefer the callout method as it
+ * avoids the need to pass a pointer using -sDisplayHandle. */
+static display_callback callbacks =
+{
+    sizeof(callbacks),
+    DISPLAY_VERSION_MAJOR,
+    DISPLAY_VERSION_MINOR,
+    open,
+    preclose,
+    close,
+    presize,
+    size,
+    sync,
+    page,
+    update,
+    memalloc,
+    memfree,
+    separation,
+    adjust_band_height,
+    rectangle_request
+};
+
+/*--------------------------------------------------------------------*/
+/* This is our callout handler. It handles callouts from devices within
+ * Ghostscript. It only handles a single callout, from the display
+ * device, to return the callback handler and callback handle. */
+static int
+callout(void *instance,
+        void *callout_handle,
+        const char *device_name,
+        int id,
+        int size,
+        void *data)
+{
+    teststate_t *ts = (teststate_t *)callout_handle;
+
+    SANITY_CHECK(ts);
+
+    /* We are only interested in callouts from the display device. */
+    if (strcmp(device_name, "display"))
+        return -1;
+
+    if (id == DISPLAY_CALLOUT_GET_CALLBACK)
+    {
+        /* Fill in the supplied block with the details of our callback
+         * handler, and the handle to use. In this instance, the handle
+         * is the pointer to our test structure. */
+        gs_display_get_callback_t *cb = (gs_display_get_callback_t *)data;
+        cb->callback = &callbacks;
+        cb->caller_handle = ts;
+        return 0;
+    }
+    return -1;
+}
+
+/* mexFunction is the gateway routine for the MEX-file.  Like the main
+   function in a C project */
+void
+mexFunction( int nlhs, mxArray *plhs[],
+             int nrhs, const mxArray *prhs[] )
+{
+    /* Set up GS to use the display device. Register the callback
+       which will callback to a MATLAB function, whose task it is
+       to deal with the rendered image data */
+    /* Make the teststate a blank slate for us to work with. */
+    teststate_t teststate = { SANITY_CHECK_VALUE };
+
+    /* Construct the argc/argv to pass to ghostscript. */
+    int argc = 0;
+    char *argv[10];
+    char format_arg[64];
+    char first_page_arg[64];
+    char last_page_arg[64];
+    char resolution_arg[64];
+    int code = 0;
+    void *instance = NULL;
+    int format, page_number;
+    size_t m, n;
+    mxDouble *value;
+    int result;
+    char *file_name = NULL;
+    int len;
+    int resolution;
+
+    /* Error checking */
+    if (nrhs != 4) {
+        mexPrintf("Incorrect number of input args");
+        return;
+    }
+
+    if (mxGetClassID(prhs[0]) != mxCHAR_CLASS || mxIsComplex(prhs[0]) ||
+        mxGetM(prhs[0]) != 1) {
+        mexErrMsgTxt("First input must be file name");
+        return;
+    }
+    len = mxGetN(prhs[0]);
+    file_name = (char *)malloc(len + 1);
+    if (file_name == NULL) {
+        mexErrMsgTxt("Filename allocation failed");
+        return;
+    }
+    code = mxGetString(prhs[0], file_name, len + 1);
+    if (code != 0) {
+        mexErrMsgTxt("Mex string copy failed");
+        return;
+    }
+
+    if (mxGetClassID(prhs[1]) != mxUINT32_CLASS || mxIsComplex(prhs[1]) ||
+        mxGetN(prhs[1]) * mxGetM(prhs[1]) != 1) {
+        mexErrMsgTxt("Second input must be data format");
+        return;
+    }
+    format = mxGetScalar(prhs[1]);
+
+    if (!mxIsDouble(prhs[2]) || mxIsComplex(prhs[2]) ||
+        mxGetN(prhs[2]) * mxGetM(prhs[2]) != 1) {
+        mexErrMsgTxt("Third input must be page number");
+        return;
+    }
+    page_number = mxGetScalar(prhs[2]);
+
+    if (!mxIsDouble(prhs[3]) || mxIsComplex(prhs[3]) ||
+        mxGetN(prhs[3]) * mxGetM(prhs[3]) != 1) {
+        mexErrMsgTxt("Fourth input must be resolution");
+        return;
+    }
+    resolution = mxGetScalar(prhs[3]);
+
+    if (!(format == PlanarGray || format == PlanarRGB ||
+        format == PlanarCMYK || format == PlanarSpots)) {
+        mexPrintf("Data format must be planar");
+        return;
+    }
+
+    if (nlhs != 1) {
+        mexPrintf("Incorrect number of output args");
+        return;
+    }
+
+    /* Set up command */
+    argv[argc++] = "gs";
+    argv[argc++] = "-sDEVICE=display";  /* Using display device to get callback*/
+    argv[argc++] = "-dNOPAUSE";
+    argv[argc++] = first_page_arg;
+    argv[argc++] = last_page_arg;
+    argv[argc++] = format_arg;
+    argv[argc++] = resolution_arg;
+
+    sprintf(first_page_arg, "-dFirstPage=%d", page_number);
+    sprintf(last_page_arg, "-dLastPage=%d", page_number);
+    sprintf(format_arg, "-dDisplayFormat=16#%x", format);
+    sprintf(resolution_arg, "-r%d", resolution);
+
+    argv[argc++] = file_name;
+
+    /* Create a GS instance. */
+    code = gsapi_new_instance(&instance, INSTANCE_HANDLE);
+    if (code < 0) {
+        mexPrintf("Error %d in gsapi_new_instance\n", code);
+        return;
+    }
+
+    /* Assign lhs variables to teststate members */
+    teststate.mex_image_data = &plhs[0];
+
+    /* Register our callout handler. This will pass the display
+     * device the callback structure and handle when requested. */
+    code = gsapi_register_callout(instance, callout, &teststate);
+    if (code < 0) {
+        mexPrintf("Error %d in gsapi_register_callout\n", code);
+        goto fail;
+    }
+
+    code = gsapi_init_with_args(instance, argc, argv);
+    if (code < 0) {
+        mexPrintf("Error %d in gsapi_init_with_args\n", code);
+        goto fail;
+    }
+
+    /* Close the interpreter down (important, or we will leak!) */
+    code = gsapi_exit(instance);
+    if (code < 0) {
+        mexPrintf("Error %d in gsapi_exit\n", code);
+    }
+
+fail:
+    /* Delete the gs instance. */
+    gsapi_delete_instance(instance);
+
+    if (file_name != NULL)
+        free(file_name);
+}
diff --git a/demos/c/Makefile b/demos/c/Makefile
index 63dc4da5..5f053410 100644
--- a/demos/c/Makefile
+++ b/demos/c/Makefile
@@ -10,3 +10,17 @@ run_api_test: api_test
 post_api_test:
 	md5sum apitest*
 	rm apitest*
+
+multi_test: multi_test.c
+	(cd ../.. && ./autogen.sh)
+	(cd ../.. && make so XCFLAGS="-DCLUSTER")
+	pwd
+	gcc -fPIC -I../.. multi_test.c -DGHOSTPDL=1 -lgpdl -lpthread -L../../sobin -o multi_test
+
+run_multi_test: multi_test
+	LD_LIBRARY_PATH=../../sobin ./multi_test
+
+post_multi_test:
+	md5sum multitest*
+	rm multitest*
+	rm multi_out*
diff --git a/demos/c/ReadMe.txt b/demos/c/ReadMe.txt
index 16c4d9de..336a31fb 100644
--- a/demos/c/ReadMe.txt
+++ b/demos/c/ReadMe.txt
@@ -29,3 +29,43 @@ tested there. Some fiddling to load the DLL may be required.
 Building with GHOSTPDL=0 will allow the Ghostscript DLL to be
 tested. The VS2019 project will need to be edited to use the
 appropriate .lib file too.
+
+On unix, the file can be built using:
+
+ make api_test
+
+run using:
+
+ make run_api_test
+
+and cleaned up using:
+
+ make post_api_test
+
+
+                            multi_test
+                            ~~~~~~~~~~
+
+This is a simple VS2019 project that loads the gpdl dll and drives
+multiple instances of it from the gsapi functions.
+
+It is intended as a simple demonstration of how to use multiple
+instances of the ghostscript library at once; in this case many
+ghostscript instances run in parallel within a single process
+to convert several different documents at a time.
+
+Building with GHOSTPDL=0 will allow the Ghostscript DLL to be
+tested. The VS2019 project will need to be edited to use the
+appropriate .lib file too.
+
+On unix, the file can be built using:
+
+ make multi_test
+
+run using:
+
+ make run_multi_test
+
+and cleaned up using:
+
+ make post_multi_test
diff --git a/demos/c/multi_test.c b/demos/c/multi_test.c
new file mode 100644
index 00000000..f62d3e6e
--- /dev/null
+++ b/demos/c/multi_test.c
@@ -0,0 +1,191 @@
+/* Copyright (C) 2018-2022 Artifex Software, Inc.
+   All Rights Reserved.
+
+   This software is provided AS-IS with no warranty, either express or
+   implied.
+
+   This software is distributed under license and may not be copied,
+   modified or distributed except as expressly authorized under the terms
+   of the license contained in the file LICENSE in this distribution.
+
+   Refer to licensing information at http://www.artifex.com or contact
+   Artifex Software, Inc.,  1305 Grant Avenue - Suite 200, Novato,
+   CA 94945, U.S.A., +1(415)492-9861, for further information.
+*/
+
+/* Simple example file to demonstrate multi-instance use of
+ * the ghostscript/GPDL library. */
+
+#ifdef _WIN32
+/* Stop windows builds complaining about sprintf being insecure. */
+#define _CRT_SECURE_NO_WARNINGS
+#include <windows.h>
+#define WINDOWS
+#else
+#include <pthread.h>
+#endif
+
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+#include <memory.h>
+#include <assert.h>
+#include <limits.h>
+#include <stdarg.h>
+#include <stdint.h>
+
+/* This can work either with the Ghostscript or GhostPDL
+ * library. The code is the same for both. */
+#if GHOSTPDL
+#include "pcl/pl/plapi.h"   /* GSAPI - gpdf version */
+#else
+#include "psi/iapi.h"       /* GSAPI - ghostscript version */
+#endif
+
+/* We hold details of each threads working in a thread_data
+ * structure. */
+typedef struct
+{
+    /* What worker number are we ? */
+    int thread_num;
+    /* What input file? should this worker use? */
+    char *in_file;
+    /* Somewhere to store the thread id */
+#ifdef WINDOWS
+    HANDLE thread;
+#else
+    pthread_t thread;
+#endif
+    /* exit code for the thread */
+    int code;
+} thread_data;
+
+/* The function to perform the work of the thread.
+ * Starts a gs instance, runs a file, shuts it down.
+ */
+static
+#ifdef WINDOWS
+DWORD WINAPI
+#else
+void *
+#endif
+worker(void *td_)
+{
+    thread_data *td = (thread_data *)td_;
+    int code;
+    void *instance  = NULL;
+    char out[32];
+
+    /* Construct the argc/argv to pass to ghostscript. */
+    int argc = 0;
+    char *argv[10];
+
+    sprintf(out, "multi_out_%d_", td->thread_num);
+    strcat(out, "%d.png");
+    argv[argc++] = "gpdl";
+    argv[argc++] = "-sDEVICE=png16m";
+    argv[argc++] = "-o";
+    argv[argc++] = out;
+    argv[argc++] = "-r100";
+    argv[argc++] = td->in_file;
+
+    /* Create a GS instance. */
+    code = gsapi_new_instance(&instance, NULL);
+    if (code < 0) {
+        printf("Error %d in gsapi_new_instance\n", code);
+        goto failearly;
+    }
+
+    /* Run our test. */
+    code = gsapi_init_with_args(instance, argc, argv);
+    if (code < 0) {
+        printf("Error %d in gsapi_init_with_args\n", code);
+        goto fail;
+    }
+
+    /* Close the interpreter down (important, or we will leak!) */
+    code = gsapi_exit(instance);
+    if (code < 0) {
+        printf("Error %d in gsapi_exit\n", code);
+        goto fail;
+    }
+
+fail:
+    /* Delete the gs instance. */
+    gsapi_delete_instance(instance);
+
+failearly:
+    td->code = code;
+
+#ifdef WINDOWS
+    return 0;
+#else
+    return NULL;
+#endif
+}
+
+/* A list of input files to run. */
+char *in_files[] =
+{
+  "../../examples/tiger.eps",
+  "../../examples/golfer.eps",
+  "../../examples/escher.ps",
+  "../../examples/snowflak.ps"
+#ifdef GHOSTPDL
+  , "../../pcl/examples/grashopp.pcl"
+  , "../../pcl/examples/owl.pcl"
+  , "../../pcl/examples/tiger.xps"
+#endif
+};
+
+#define NUM_INPUTS (sizeof(in_files)/sizeof(*in_files))
+#define NUM_WORKERS (10)
+
+int main(int argc, char *argv[])
+{
+    int failed = 0;
+#ifndef WINDOWS
+    int code;
+#endif
+    int i;
+    thread_data td[NUM_WORKERS];
+
+    /* Start NUM_WORKERS threads */
+    for (i = 0; i < NUM_WORKERS; i++)
+    {
+        td[i].in_file = in_files[i % NUM_INPUTS];
+        td[i].thread_num = i;
+
+#ifdef WINDOWS
+        td[i].thread = CreateThread(NULL, 0, worker, &td[i], 0, NULL);
+#else
+        code = pthread_create(&td[i].thread, NULL, worker, &td[i]);
+        if (code != 0) {
+            fprintf(stderr, "Thread %d creation failed\n", i);
+            exit(1);
+        }
+#endif
+    }
+
+    /* Wait for them all to finish */
+    for (i = 0; i < NUM_WORKERS; i++)
+    {
+        void *status = NULL;
+
+#ifdef WINDOWS
+        WaitForSingleObject(td[i].thread, INFINITE);
+#else
+        code = pthread_join(td[i].thread, &status);
+        if (code != 0) {
+            fprintf(stderr, "Thread join %d failed\n", i);
+            exit(1);
+        }
+#endif
+        /* All the threads should return with 0 */
+        if (td[i].code != 0)
+            failed = 1;
+        fprintf(stderr, "Thread %d finished with %d\n", i, td[i].code);
+    }
+
+    return failed;
+}
diff --git a/demos/c/multi_test.vcxproj b/demos/c/multi_test.vcxproj
new file mode 100644
index 00000000..ae208c5d
--- /dev/null
+++ b/demos/c/multi_test.vcxproj
@@ -0,0 +1,239 @@
+<?xml version="1.0" encoding="utf-8"?>
+<Project DefaultTargets="Build" xmlns="http://schemas.microsoft.com/developer/msbuild/2003">
+  <ItemGroup Label="ProjectConfigurations">
+    <ProjectConfiguration Include="Debug|Win32">
+      <Configuration>Debug</Configuration>
+      <Platform>Win32</Platform>
+    </ProjectConfiguration>
+    <ProjectConfiguration Include="Memento|Win32">
+      <Configuration>Memento</Configuration>
+      <Platform>Win32</Platform>
+    </ProjectConfiguration>
+    <ProjectConfiguration Include="Memento|x64">
+      <Configuration>Memento</Configuration>
+      <Platform>x64</Platform>
+    </ProjectConfiguration>
+    <ProjectConfiguration Include="Release|Win32">
+      <Configuration>Release</Configuration>
+      <Platform>Win32</Platform>
+    </ProjectConfiguration>
+    <ProjectConfiguration Include="Debug|x64">
+      <Configuration>Debug</Configuration>
+      <Platform>x64</Platform>
+    </ProjectConfiguration>
+    <ProjectConfiguration Include="Release|x64">
+      <Configuration>Release</Configuration>
+      <Platform>x64</Platform>
+    </ProjectConfiguration>
+  </ItemGroup>
+  <PropertyGroup Label="Globals">
+    <VCProjectVersion>16.0</VCProjectVersion>
+    <Keyword>Win32Proj</Keyword>
+    <ProjectGuid>{6f11d63a-3533-47e5-8aa8-973d804443a0}</ProjectGuid>
+    <RootNamespace>multi_test</RootNamespace>
+    <WindowsTargetPlatformVersion>10.0</WindowsTargetPlatformVersion>
+  </PropertyGroup>
+  <Import Project="$(VCTargetsPath)\Microsoft.Cpp.Default.props" />
+  <PropertyGroup Condition="'$(Configuration)|$(Platform)'=='Debug|Win32'" Label="Configuration">
+    <ConfigurationType>Application</ConfigurationType>
+    <UseDebugLibraries>true</UseDebugLibraries>
+    <PlatformToolset>v142</PlatformToolset>
+    <CharacterSet>Unicode</CharacterSet>
+  </PropertyGroup>
+  <PropertyGroup Condition="'$(Configuration)|$(Platform)'=='Memento|Win32'" Label="Configuration">
+    <ConfigurationType>Application</ConfigurationType>
+    <UseDebugLibraries>true</UseDebugLibraries>
+    <PlatformToolset>v142</PlatformToolset>
+    <CharacterSet>Unicode</CharacterSet>
+  </PropertyGroup>
+  <PropertyGroup Condition="'$(Configuration)|$(Platform)'=='Release|Win32'" Label="Configuration">
+    <ConfigurationType>Application</ConfigurationType>
+    <UseDebugLibraries>false</UseDebugLibraries>
+    <PlatformToolset>v142</PlatformToolset>
+    <WholeProgramOptimization>true</WholeProgramOptimization>
+    <CharacterSet>Unicode</CharacterSet>
+  </PropertyGroup>
+  <PropertyGroup Condition="'$(Configuration)|$(Platform)'=='Debug|x64'" Label="Configuration">
+    <ConfigurationType>Application</ConfigurationType>
+    <UseDebugLibraries>true</UseDebugLibraries>
+    <PlatformToolset>v142</PlatformToolset>
+    <CharacterSet>Unicode</CharacterSet>
+  </PropertyGroup>
+  <PropertyGroup Condition="'$(Configuration)|$(Platform)'=='Memento|x64'" Label="Configuration">
+    <ConfigurationType>Application</ConfigurationType>
+    <UseDebugLibraries>true</UseDebugLibraries>
+    <PlatformToolset>v142</PlatformToolset>
+    <CharacterSet>Unicode</CharacterSet>
+  </PropertyGroup>
+  <PropertyGroup Condition="'$(Configuration)|$(Platform)'=='Release|x64'" Label="Configuration">
+    <ConfigurationType>Application</ConfigurationType>
+    <UseDebugLibraries>false</UseDebugLibraries>
+    <PlatformToolset>v142</PlatformToolset>
+    <WholeProgramOptimization>true</WholeProgramOptimization>
+    <CharacterSet>Unicode</CharacterSet>
+  </PropertyGroup>
+  <Import Project="$(VCTargetsPath)\Microsoft.Cpp.props" />
+  <ImportGroup Label="ExtensionSettings">
+  </ImportGroup>
+  <ImportGroup Label="Shared">
+  </ImportGroup>
+  <ImportGroup Label="PropertySheets" Condition="'$(Configuration)|$(Platform)'=='Debug|Win32'">
+    <Import Project="$(UserRootDir)\Microsoft.Cpp.$(Platform).user.props" Condition="exists('$(UserRootDir)\Microsoft.Cpp.$(Platform).user.props')" Label="LocalAppDataPlatform" />
+  </ImportGroup>
+  <ImportGroup Condition="'$(Configuration)|$(Platform)'=='Memento|Win32'" Label="PropertySheets">
+    <Import Project="$(UserRootDir)\Microsoft.Cpp.$(Platform).user.props" Condition="exists('$(UserRootDir)\Microsoft.Cpp.$(Platform).user.props')" Label="LocalAppDataPlatform" />
+  </ImportGroup>
+  <ImportGroup Label="PropertySheets" Condition="'$(Configuration)|$(Platform)'=='Release|Win32'">
+    <Import Project="$(UserRootDir)\Microsoft.Cpp.$(Platform).user.props" Condition="exists('$(UserRootDir)\Microsoft.Cpp.$(Platform).user.props')" Label="LocalAppDataPlatform" />
+  </ImportGroup>
+  <ImportGroup Label="PropertySheets" Condition="'$(Configuration)|$(Platform)'=='Debug|x64'">
+    <Import Project="$(UserRootDir)\Microsoft.Cpp.$(Platform).user.props" Condition="exists('$(UserRootDir)\Microsoft.Cpp.$(Platform).user.props')" Label="LocalAppDataPlatform" />
+  </ImportGroup>
+  <ImportGroup Condition="'$(Configuration)|$(Platform)'=='Memento|x64'" Label="PropertySheets">
+    <Import Project="$(UserRootDir)\Microsoft.Cpp.$(Platform).user.props" Condition="exists('$(UserRootDir)\Microsoft.Cpp.$(Platform).user.props')" Label="LocalAppDataPlatform" />
+  </ImportGroup>
+  <ImportGroup Label="PropertySheets" Condition="'$(Configuration)|$(Platform)'=='Release|x64'">
+    <Import Project="$(UserRootDir)\Microsoft.Cpp.$(Platform).user.props" Condition="exists('$(UserRootDir)\Microsoft.Cpp.$(Platform).user.props')" Label="LocalAppDataPlatform" />
+  </ImportGroup>
+  <PropertyGroup Label="UserMacros" />
+  <PropertyGroup Condition="'$(Configuration)|$(Platform)'=='Debug|Win32'">
+    <LinkIncremental>true</LinkIncremental>
+    <OutDir>$(ProjectDir)..\..\debugbin\</OutDir>
+    <TargetName>$(ProjectName)</TargetName>
+  </PropertyGroup>
+  <PropertyGroup Condition="'$(Configuration)|$(Platform)'=='Memento|Win32'">
+    <LinkIncremental>true</LinkIncremental>
+    <OutDir>$(ProjectDir)..\..\membin\</OutDir>
+    <TargetName>$(ProjectName)</TargetName>
+  </PropertyGroup>
+  <PropertyGroup Condition="'$(Configuration)|$(Platform)'=='Release|Win32'">
+    <LinkIncremental>false</LinkIncremental>
+    <OutDir>$(ProjectDir)..\..\bin\</OutDir>
+    <TargetName>$(ProjectName)</TargetName>
+  </PropertyGroup>
+  <PropertyGroup Condition="'$(Configuration)|$(Platform)'=='Debug|x64'">
+    <LinkIncremental>true</LinkIncremental>
+    <TargetName>$(ProjectName)64</TargetName>
+    <OutDir>$(ProjectDir)..\..\debugbin\</OutDir>
+  </PropertyGroup>
+  <PropertyGroup Condition="'$(Configuration)|$(Platform)'=='Memento|x64'">
+    <LinkIncremental>true</LinkIncremental>
+    <OutDir>$(ProjectDir)..\..\membin\</OutDir>
+    <TargetName>$(ProjectName)64</TargetName>
+  </PropertyGroup>
+  <PropertyGroup Condition="'$(Configuration)|$(Platform)'=='Release|x64'">
+    <LinkIncremental>false</LinkIncremental>
+    <OutDir>$(ProjectDir)..\..\bin\</OutDir>
+    <TargetName>$(ProjectName)64</TargetName>
+  </PropertyGroup>
+  <ItemDefinitionGroup Condition="'$(Configuration)|$(Platform)'=='Debug|Win32'">
+    <ClCompile>
+      <WarningLevel>Level3</WarningLevel>
+      <SDLCheck>true</SDLCheck>
+      <PreprocessorDefinitions>GHOSTPDL;WIN32;_DEBUG;_CONSOLE;%(PreprocessorDefinitions)</PreprocessorDefinitions>
+      <ConformanceMode>true</ConformanceMode>
+      <AdditionalIncludeDirectories>..\..</AdditionalIncludeDirectories>
+    </ClCompile>
+    <Link>
+      <SubSystem>Console</SubSystem>
+      <GenerateDebugInformation>true</GenerateDebugInformation>
+      <AdditionalDependencies>gpdldll32.lib;%(AdditionalDependencies)</AdditionalDependencies>
+      <AdditionalLibraryDirectories>..\..\debugbin</AdditionalLibraryDirectories>
+    </Link>
+    <PostBuildEvent>
+      <Command>
+      </Command>
+    </PostBuildEvent>
+  </ItemDefinitionGroup>
+  <ItemDefinitionGroup Condition="'$(Configuration)|$(Platform)'=='Memento|Win32'">
+    <ClCompile>
+      <WarningLevel>Level3</WarningLevel>
+      <SDLCheck>true</SDLCheck>
+      <PreprocessorDefinitions>GHOSTPDL;MEMENTO;WIN32;_DEBUG;_CONSOLE;%(PreprocessorDefinitions)</PreprocessorDefinitions>
+      <ConformanceMode>true</ConformanceMode>
+      <AdditionalIncludeDirectories>..\..</AdditionalIncludeDirectories>
+    </ClCompile>
+    <Link>
+      <SubSystem>Console</SubSystem>
+      <GenerateDebugInformation>true</GenerateDebugInformation>
+      <AdditionalDependencies>gpdldll32.lib;%(AdditionalDependencies)</AdditionalDependencies>
+      <AdditionalLibraryDirectories>..\..\membin</AdditionalLibraryDirectories>
+    </Link>
+    <PostBuildEvent>
+      <Command>
+      </Command>
+    </PostBuildEvent>
+  </ItemDefinitionGroup>
+  <ItemDefinitionGroup Condition="'$(Configuration)|$(Platform)'=='Release|Win32'">
+    <ClCompile>
+      <WarningLevel>Level3</WarningLevel>
+      <FunctionLevelLinking>true</FunctionLevelLinking>
+      <IntrinsicFunctions>true</IntrinsicFunctions>
+      <SDLCheck>true</SDLCheck>
+      <PreprocessorDefinitions>GHOSTPDL;WIN32;NDEBUG;_CONSOLE;%(PreprocessorDefinitions)</PreprocessorDefinitions>
+      <ConformanceMode>true</ConformanceMode>
+      <AdditionalIncludeDirectories>..\..</AdditionalIncludeDirectories>
+    </ClCompile>
+    <Link>
+      <SubSystem>Console</SubSystem>
+      <EnableCOMDATFolding>true</EnableCOMDATFolding>
+      <OptimizeReferences>true</OptimizeReferences>
+      <GenerateDebugInformation>true</GenerateDebugInformation>
+      <AdditionalDependencies>gpdldll32.lib;%(AdditionalDependencies)</AdditionalDependencies>
+      <AdditionalLibraryDirectories>..\..\bin</AdditionalLibraryDirectories>
+    </Link>
+  </ItemDefinitionGroup>
+  <ItemDefinitionGroup Condition="'$(Configuration)|$(Platform)'=='Debug|x64'">
+    <ClCompile>
+      <WarningLevel>Level3</WarningLevel>
+      <SDLCheck>true</SDLCheck>
+      <PreprocessorDefinitions>_DEBUG;_CONSOLE;%(PreprocessorDefinitions)</PreprocessorDefinitions>
+      <ConformanceMode>true</ConformanceMode>
+      <AdditionalIncludeDirectories>..\..</AdditionalIncludeDirectories>
+    </ClCompile>
+    <Link>
+      <SubSystem>Console</SubSystem>
+      <GenerateDebugInformation>true</GenerateDebugInformation>
+      <AdditionalDependencies>gpdldll64.lib;%(AdditionalDependencies)</AdditionalDependencies>
+      <AdditionalLibraryDirectories>..\..\debugbin</AdditionalLibraryDirectories>
+    </Link>
+  </ItemDefinitionGroup>
+  <ItemDefinitionGroup Condition="'$(Configuration)|$(Platform)'=='Memento|x64'">
+    <ClCompile>
+      <WarningLevel>Level3</WarningLevel>
+      <SDLCheck>true</SDLCheck>
+      <PreprocessorDefinitions>MEMENTO;_DEBUG;_CONSOLE;%(PreprocessorDefinitions)</PreprocessorDefinitions>
+      <ConformanceMode>true</ConformanceMode>
+      <AdditionalIncludeDirectories>..\..</AdditionalIncludeDirectories>
+    </ClCompile>
+    <Link>
+      <SubSystem>Console</SubSystem>
+      <GenerateDebugInformation>true</GenerateDebugInformation>
+      <AdditionalDependencies>gpdldll64.lib;%(AdditionalDependencies)</AdditionalDependencies>
+      <AdditionalLibraryDirectories>..\..\membin</AdditionalLibraryDirectories>
+    </Link>
+  </ItemDefinitionGroup>
+  <ItemDefinitionGroup Condition="'$(Configuration)|$(Platform)'=='Release|x64'">
+    <ClCompile>
+      <WarningLevel>Level3</WarningLevel>
+      <FunctionLevelLinking>true</FunctionLevelLinking>
+      <IntrinsicFunctions>true</IntrinsicFunctions>
+      <SDLCheck>true</SDLCheck>
+      <PreprocessorDefinitions>NDEBUG;_CONSOLE;%(PreprocessorDefinitions)</PreprocessorDefinitions>
+      <ConformanceMode>true</ConformanceMode>
+    </ClCompile>
+    <Link>
+      <SubSystem>Console</SubSystem>
+      <EnableCOMDATFolding>true</EnableCOMDATFolding>
+      <OptimizeReferences>true</OptimizeReferences>
+      <GenerateDebugInformation>true</GenerateDebugInformation>
+      <AdditionalLibraryDirectories>..\..\bin</AdditionalLibraryDirectories>
+    </Link>
+  </ItemDefinitionGroup>
+  <ItemGroup>
+    <ClCompile Include="multi_test.c" />
+  </ItemGroup>
+  <Import Project="$(VCTargetsPath)\Microsoft.Cpp.targets" />
+  <ImportGroup Label="ExtensionTargets">
+  </ImportGroup>
+</Project>
\ No newline at end of file
diff --git a/demos/c/multi_test.vcxproj.filters b/demos/c/multi_test.vcxproj.filters
new file mode 100644
index 00000000..0e2de063
--- /dev/null
+++ b/demos/c/multi_test.vcxproj.filters
@@ -0,0 +1,14 @@
+<?xml version="1.0" encoding="utf-8"?>
+<Project ToolsVersion="4.0" xmlns="http://schemas.microsoft.com/developer/msbuild/2003">
+  <ItemGroup>
+    <Filter Include="Source Files">
+      <UniqueIdentifier>{4FC737F1-C7A5-4376-A066-2A32D752A2FF}</UniqueIdentifier>
+      <Extensions>cpp;c;cc;cxx;c++;def;odl;idl;hpj;bat;asm;asmx</Extensions>
+    </Filter>
+  </ItemGroup>
+  <ItemGroup>
+    <ClCompile Include="multi_test.c">
+      <Filter>Source Files</Filter>
+    </ClCompile>
+  </ItemGroup>
+</Project>
diff --git a/demos/java/README.txt b/demos/java/README.txt
index 4781bb09..3e94a920 100644
--- a/demos/java/README.txt
+++ b/demos/java/README.txt
@@ -6,3 +6,12 @@ variable. This exposes command line programs to build Java
 applications.
 
 On Linux and Mac, OpenJDK 8 is used.
+
+What's in this directory:
+
+./gsjava	The Java project which provides the bindings to Ghostscript.
+./gstest	An old project used for testing gsjava
+./gsviewer	A demo Java PDF viewer made using the Java bindings
+./jni		Contains the C++ project which backs the Java bindings to Ghostscript
+./mtdemo	A demo project used to demonstrate how multithreading can be used with
+			the Java bindings
\ No newline at end of file
diff --git a/demos/java/gsjava/build_darwin.sh b/demos/java/gsjava/build_darwin.sh
index 212dfb36..460e9ee0 100644
--- a/demos/java/gsjava/build_darwin.sh
+++ b/demos/java/gsjava/build_darwin.sh
@@ -2,8 +2,6 @@
 
 mkdir -p bin
 
-echo "Compiling gs_jni C++ source..."
-
 cd "../jni/gs_jni"
 
 bash build_darwin.sh
diff --git a/demos/java/gsjava/build_linux.sh b/demos/java/gsjava/build_linux.sh
index 2866c07e..290540ae 100644
--- a/demos/java/gsjava/build_linux.sh
+++ b/demos/java/gsjava/build_linux.sh
@@ -2,8 +2,6 @@
 
 mkdir -p bin
 
-echo "Compiling gs_jni C++ source..."
-
 cd "../jni/gs_jni"
 
 bash build_linux.sh
diff --git a/demos/java/gsjava/build_win32.bat b/demos/java/gsjava/build_win32.bat
index 88757811..85b81abc 100644
--- a/demos/java/gsjava/build_win32.bat
+++ b/demos/java/gsjava/build_win32.bat
@@ -2,7 +2,7 @@
 
 if not exist bin mkdir bin
 
-echo Compiling Java source...
+echo Compiling gsjava Java source...
 javac -sourcepath src\ -d bin^
 	src\com\artifex\gsjava\GSAPI.java^
 	src\com\artifex\gsjava\GSInstance.java^
@@ -53,7 +53,6 @@ jar -cf ..\gsjava.jar^
 	com\artifex\gsjava\GSAPI.class^
 	com\artifex\gsjava\GSAPI$Revision.class^
 	com\artifex\gsjava\GSInstance.class^
-	com\artifex\gsjava\GSInstance$1.class^
 	com\artifex\gsjava\GSInstance$GSParam.class^
 	com\artifex\gsjava\GSInstance$ParamIterator.class^
 	^
@@ -74,7 +73,6 @@ jar -cf ..\gsjava.jar^
 	^
 	com\artifex\gsjava\devices\BMPDevice.class^
 	com\artifex\gsjava\devices\Device.class^
-	com\artifex\gsjava\devices\Device$1.class^
 	com\artifex\gsjava\devices\Device$StdIO.class^
 	com\artifex\gsjava\devices\DeviceInUseException.class^
 	com\artifex\gsjava\devices\DeviceNotSupportedException.class^
diff --git a/demos/java/gsjava/src/com/artifex/gsjava/GSAPI.java b/demos/java/gsjava/src/com/artifex/gsjava/GSAPI.java
index 652d4356..6ab49bb2 100644
--- a/demos/java/gsjava/src/com/artifex/gsjava/GSAPI.java
+++ b/demos/java/gsjava/src/com/artifex/gsjava/GSAPI.java
@@ -59,7 +59,7 @@ public class GSAPI {
 	public static final long GS_NULL = 0L;
 
 	/**
-	 * Error codes
+	 * Level 1 error codes
 	 */
 	public static final int GS_ERROR_OK = 0,
 							GS_ERROR_UNKNOWNERROR = -1,
@@ -89,7 +89,7 @@ public class GSAPI {
 							GS_ERROR_VMERROR = -25;
 
 	/**
-	 * Error codes
+	 * Level 2 error codes
 	 */
 	public static final int GS_ERROR_CONFIGURATION_ERROR = -26,
 							GS_ERROR_UNDEFINEDRESOURCE = -27,
@@ -97,6 +97,12 @@ public class GSAPI {
 							GS_ERROR_INVALIDCONTEXT = -29,
 							GS_ERROR_INVALID = -30;
 
+	/**
+	 * Psuedo-errors used internally
+	 */
+	public static final int GS_ERROR_HIT_DETECTED = -59,
+							GS_ERROR_FATAL = -100;
+
 	public static final int GS_COLORS_NATIVE = (1 << 0),
 							GS_COLORS_GRAY = (1 << 1),
 							GS_COLORS_RGB = (1 << 2),
diff --git a/demos/java/gsjava/src/com/artifex/gsjava/GSInstance.java b/demos/java/gsjava/src/com/artifex/gsjava/GSInstance.java
index e5e713c7..ff3dbafa 100644
--- a/demos/java/gsjava/src/com/artifex/gsjava/GSInstance.java
+++ b/demos/java/gsjava/src/com/artifex/gsjava/GSInstance.java
@@ -75,13 +75,22 @@ public class GSInstance implements Iterable<GSInstance.GSParam<?>> {
 		}
 	}
 
-	private static volatile boolean instanceExists = false;
+	private static boolean ALLOW_MULTITHREADING = false;
+	private static volatile int INSTANCES = 0;
+
+	public static void setAllowMultithreading(boolean state) {
+		ALLOW_MULTITHREADING = state;
+	}
+
+	public static int getInstanceCount() {
+		return INSTANCES;
+	}
 
 	private long instance;
 	private long callerHandle;
 
 	public GSInstance(long callerHandle) throws IllegalStateException {
-		if (instanceExists)
+		if (!ALLOW_MULTITHREADING && INSTANCES > 0)
 			throw new IllegalStateException("An instance already exists");
 		Reference<Long> ref = new Reference<>();
 		int ret = gsapi_new_instance(ref, callerHandle);
@@ -89,7 +98,7 @@ public class GSInstance implements Iterable<GSInstance.GSParam<?>> {
 			throw new IllegalStateException("Failed to create new instance: " + ret);
 		this.instance = ref.getValue();
 		this.callerHandle = callerHandle;
-		instanceExists = true;
+		INSTANCES++;
 	}
 
 	public GSInstance() throws IllegalStateException {
@@ -97,10 +106,11 @@ public class GSInstance implements Iterable<GSInstance.GSParam<?>> {
 	}
 
 	public void delete_instance() {
-		if (instance != GS_NULL)
+		if (instance != GS_NULL) {
 			gsapi_delete_instance(instance);
-		instance = GS_NULL;
-		instanceExists = false;
+			instance = GS_NULL;
+			INSTANCES--;
+		}
 	}
 
 	public int set_stdio(IStdInFunction stdin, IStdOutFunction stdout, IStdErrFunction stderr) {
diff --git a/demos/java/gsviewer/README.txt b/demos/java/gsviewer/README.txt
index 2808fed9..1b4776fe 100644
--- a/demos/java/gsviewer/README.txt
+++ b/demos/java/gsviewer/README.txt
@@ -48,10 +48,10 @@ Building:
 
 -= WINDOWS =-
 
-Ensure both gs_jni.dll and gpdldll64.dll. Then, run the build_win32.bat script.
-This will automatically build and copy gsjava.jar to this directory. To run,
-open gsviewer.jar either through File Explorer or in the command line through
-the following command:
+Ensure both gs_jni.dll and gpdldll64.dll are built. Then, run the
+build_win32.bat script. This will automatically build and copy gsjava.jar to
+this directory. To run, open gsviewer.jar either through File Explorer or in
+the command line through the following command:
 
 java -jar gsviewer.jar
 
@@ -67,4 +67,4 @@ directories. gsviewer.jar will be outputted in this directory.
 Ensure Ghostscript has been built.
 Run the build_darwin.sh script. This will automatically build
 gs_jni.dylib, gsjava.jar, and copy the files to the needed
-directories. gsviewer.jar will be outputed in this directory.
+directories. gsviewer.jar will be outputed in this directory.
\ No newline at end of file
diff --git a/demos/java/gsviewer/build_darwin.sh b/demos/java/gsviewer/build_darwin.sh
index 6c9d96c7..ff9ec5b9 100644..100755
--- a/demos/java/gsviewer/build_darwin.sh
+++ b/demos/java/gsviewer/build_darwin.sh
@@ -34,4 +34,18 @@ javac -sourcepath src/ -d bin/ \
 cd bin
 
 echo "Packing gsviewer JAR file..."
-jar cfm "../gsviewer.jar" "../Manifest.md" "com/"
\ No newline at end of file
+jar cfm "../gsviewer.jar" "../Manifest.md" "com/"
+
+
+echo "Copy gs_jni.dylib"
+cp "../jni/gs_jni/gs_jni.dylib" "gs_jni.dylib"
+
+echo "Create libgpdl.dylib link"
+cp "../../../sobin/libgpdl.dylib" "libgpdl.dylib"
+
+cd ../../../sobin
+
+echo "Copy libgpdl.dylib target"
+cp $(readlink "libgpdl.dylib") "../demos/java/gsviewer"
+
+cd ../demos/java/gsviewer
\ No newline at end of file
diff --git a/demos/java/gsviewer/build_linux.sh b/demos/java/gsviewer/build_linux.sh
index 67b3e9cf..3cd70616 100644..100755
--- a/demos/java/gsviewer/build_linux.sh
+++ b/demos/java/gsviewer/build_linux.sh
@@ -34,4 +34,18 @@ javac -sourcepath src/ -d bin/ \
 cd bin
 
 echo "Packing gsviewer JAR file..."
-jar cfm "../gsviewer.jar" "../Manifest.md" "com/"
\ No newline at end of file
+jar cfm "../gsviewer.jar" "../Manifest.md" "com/"
+
+
+echo "Copy gs_jni.so"
+cp "../jni/gs_jni/gs_jni.so" "gs_jni.so"
+
+echo "Create libgpdl.so link"
+cp "../../../sobin/libgpdl.so" "libgpdl.so"
+
+cd ../../../sobin
+
+echo "Copy libgpdl.so target"
+cp $(readlink "libgpdl.so")  "../demos/java/gsviewer"
+
+cd ../demos/java/gsviewer
\ No newline at end of file
diff --git a/demos/java/gsviewer/build_win32.bat b/demos/java/gsviewer/build_win32.bat
index 0e279e9f..0e279e9f 100644..100755
--- a/demos/java/gsviewer/build_win32.bat
+++ b/demos/java/gsviewer/build_win32.bat
diff --git a/demos/java/gsviewer/start_darwin.sh b/demos/java/gsviewer/start_darwin.sh
index 9e4004bd..9e4004bd 100644..100755
--- a/demos/java/gsviewer/start_darwin.sh
+++ b/demos/java/gsviewer/start_darwin.sh
diff --git a/demos/java/gsviewer/start_linux.sh b/demos/java/gsviewer/start_linux.sh
index 4ed9f514..4ed9f514 100644..100755
--- a/demos/java/gsviewer/start_linux.sh
+++ b/demos/java/gsviewer/start_linux.sh
diff --git a/demos/java/jni/gs_jni/build_darwin.sh b/demos/java/jni/gs_jni/build_darwin.sh
index 81b10c01..18e12cae 100644
--- a/demos/java/jni/gs_jni/build_darwin.sh
+++ b/demos/java/jni/gs_jni/build_darwin.sh
@@ -46,6 +46,16 @@ g++ -c -Wall -O3 -fPIC \
 	"jni_util.cpp" \
 	-o "obin/jni_util.o"
 
+echo "Compile instance_data.cpp"
+g++ -c -Wall -O3 -fPIC \
+	-std=c++14 \
+	-I./include \
+	-I./include/darwin \
+	-I./../../../../psi \
+	-I./../../../../devices \
+	"instance_data.cpp" \
+	-o "obin/instance_data.o"
+
 echo "Link"
 g++ -dynamiclib -fPIC \
 	-Wl \
@@ -54,4 +64,5 @@ g++ -dynamiclib -fPIC \
 	"obin/com_artifex_gsjava_GSAPI.o" \
 	"obin/com_artifex_gsjava_util_NativePointer.o" \
 	"obin/jni_util.o" \
+	"obin/instance_data.o" \
 	"../../../../sobin/libgpdl.dylib"
\ No newline at end of file
diff --git a/demos/java/jni/gs_jni/build_linux.sh b/demos/java/jni/gs_jni/build_linux.sh
index 974dfba3..f66a4883 100644
--- a/demos/java/jni/gs_jni/build_linux.sh
+++ b/demos/java/jni/gs_jni/build_linux.sh
@@ -7,7 +7,7 @@ mkdir -p obin
 echo "Compiling gs_jni C++ source..."
 
 echo "Compile callbacks.cpp"
-g++ -c -Wall -O3 \
+g++ -c -Wall -O3 -fPIC \
 	-std=c++14 \
 	-I./include \
 	-I./include/linux \
@@ -17,7 +17,7 @@ g++ -c -Wall -O3 \
 	-o "obin/callbacks.o"
 
 echo "Compile com_artifex_gsjava_GSAPI.cpp"
-g++ -c -Wall -O3 \
+g++ -c -Wall -O3 -fPIC \
 	-std=c++14 \
 	-I./include \
 	-I./include/linux \
@@ -27,7 +27,7 @@ g++ -c -Wall -O3 \
 	-o "obin/com_artifex_gsjava_GSAPI.o"
 
 echo "Compile com_artifex_gsjava_util_NativePointer.cpp"
-g++ -c -Wall -O3 \
+g++ -c -Wall -O3 -fPIC \
 	-std=c++14 \
 	-I./include \
 	-I./include/linux \
@@ -37,7 +37,7 @@ g++ -c -Wall -O3 \
 	-o "obin/com_artifex_gsjava_util_NativePointer.o"
 
 echo "Compile jni_util.cpp"
-g++ -c -Wall -O3\
+g++ -c -Wall -O3 -fPIC \
 	-std=c++14 \
 	-I./include \
 	-I./include/linux \
@@ -46,6 +46,16 @@ g++ -c -Wall -O3\
 	"jni_util.cpp" \
 	-o "obin/jni_util.o"
 
+echo "Compile instance_data.cpp"
+g++ -c -Wall -O3 -fPIC \
+	-std=c++14 \
+	-I./include \
+	-I./include/linux \
+	-I./../../../../psi \
+	-I./../../../../devices \
+	"instance_data.cpp" \
+	-o "obin/instance_data.o"
+
 echo "Link"
 g++ -shared \
 	-Wl,-soname,gs_jni.so \
@@ -54,4 +64,5 @@ g++ -shared \
 	"obin/com_artifex_gsjava_GSAPI.o" \
 	"obin/com_artifex_gsjava_util_NativePointer.o" \
 	"obin/jni_util.o" \
-	"../../../../sobin/libgpdl.so"
\ No newline at end of file
+	"obin/instance_data.o" \
+	"../../../../sobin/libgpdl.so"
diff --git a/demos/java/jni/gs_jni/callbacks.cpp b/demos/java/jni/gs_jni/callbacks.cpp
index 7826b328..2d0da54e 100644
--- a/demos/java/jni/gs_jni/callbacks.cpp
+++ b/demos/java/jni/gs_jni/callbacks.cpp
@@ -1,8 +1,11 @@
 #include "callbacks.h"
 
 #include "jni_util.h"
+#include "instance_data.h"
 
 #include <string.h>
+#include <unordered_map>
+#include <assert.h>
 
 #define STDIN_SIG "(J[BI)I"
 #define STDOUT_SIG "(J[BI)I"
@@ -31,134 +34,150 @@ Lcom/artifex/gsjava/IntReference;)I"
 
 using namespace util;
 
-static JNIEnv *g_env = NULL;
-
-static jobject g_stdIn = NULL;
-static jobject g_stdOut = NULL;
-static jobject g_stdErr = NULL;
-
-static jobject g_poll = NULL;
-
-static jobject g_displayCallback = NULL;
-
-static jobject g_callout = NULL;
-
-void callbacks::setJNIEnv(JNIEnv *env)
+void callbacks::setJNIEnv(GSInstanceData *idata, JNIEnv *env)
 {
-	g_env = env;
+	idata->env = env;
 }
 
-void callbacks::setIOCallbacks(jobject stdIn, jobject stdOut, jobject stdErr)
+void callbacks::setIOCallbacks(GSInstanceData *idata, jobject stdIn, jobject stdOut, jobject stdErr)
 {
-	if (g_env)
+	if (idata->env)
 	{
-		if (g_stdIn)
-			g_env->DeleteGlobalRef(g_stdIn);
+		if (idata->stdIn)
+			idata->env->DeleteGlobalRef(idata->stdIn);
 
-		if (g_stdOut)
-			g_env->DeleteGlobalRef(g_stdOut);
+		if (idata->stdOut)
+			idata->env->DeleteGlobalRef(idata->stdOut);
 
-		if (g_stdErr)
-			g_env->DeleteGlobalRef(g_stdErr);
+		if (idata->stdErr)
+			idata->env->DeleteGlobalRef(idata->stdErr);
 
-		g_stdIn = g_env->NewGlobalRef(stdIn);
-		g_stdOut = g_env->NewGlobalRef(stdOut);
-		g_stdErr = g_env->NewGlobalRef(stdErr);
+		idata->stdIn = idata->env->NewGlobalRef(stdIn);
+		idata->stdOut = idata->env->NewGlobalRef(stdOut);
+		idata->stdErr = idata->env->NewGlobalRef(stdErr);
 	}
 }
 
 int callbacks::stdInFunction(void *callerHandle, char *buf, int len)
 {
-	int code = 0;
-	if (g_env && g_stdIn)
-	{
-		jbyteArray byteArray = g_env->NewByteArray(len);
-		g_env->SetByteArrayRegion(byteArray, 0, len, (jbyte *)buf);
-		code = callIntMethod(g_env, g_stdIn, "onStdIn", STDIN_SIG, (jlong)callerHandle, byteArray, (jint)len);
-	}
-	return code;
+	GSInstanceData *gsdata = (GSInstanceData *)callerHandle;
+	assert(gsdata);
+
+	if (!gsdata->env || !gsdata->stdErr) return 0;
+
+	jbyteArray byteArray = gsdata->env->NewByteArray(len);
+	gsdata->env->SetByteArrayRegion(byteArray, 0, len, (jbyte *)buf);
+
+	jint result = callIntMethod(gsdata->env, gsdata->stdIn, "onStdIn", STDIN_SIG, (jlong)gsdata->stdioHandle, byteArray, (jint)len);
+	if (gsdata->env->ExceptionCheck()) return 0;
+
+	jboolean isCopy = JNI_FALSE;
+	jbyte *arr = gsdata->env->GetByteArrayElements(byteArray, &isCopy);
+
+	jsize copySize = result < len ? result : len;
+	memcpy(buf, arr, copySize);
+
+	return copySize;
 }
 
 int callbacks::stdOutFunction(void *callerHandle, const char *str, int len)
 {
-	int code = 0;
-	if (g_env && g_stdOut)
-	{
-		jbyteArray byteArray = g_env->NewByteArray(len);
-		g_env->SetByteArrayRegion(byteArray, 0, len, (const jbyte *)str);
-		code = callIntMethod(g_env, g_stdOut, "onStdOut", STDOUT_SIG, (jlong)callerHandle, byteArray, (jint)len);
-	}
-	return code;
+	GSInstanceData *gsdata = (GSInstanceData *)callerHandle;
+	assert(gsdata);
+
+	if (!gsdata->env || !gsdata->stdOut) return len;
+
+	jbyteArray byteArray = gsdata->env->NewByteArray(len);
+	gsdata->env->SetByteArrayRegion(byteArray, 0, len, (const jbyte *)str);
+
+	jint result = callIntMethod(gsdata->env, gsdata->stdOut, "onStdOut", STDOUT_SIG, (jlong)gsdata->stdioHandle, byteArray, (jint)len);
+	if (gsdata->env->ExceptionCheck()) return 0;
+
+	return result;
 }
 
 int callbacks::stdErrFunction(void *callerHandle, const char *str, int len)
 {
-	int code = 0;
-	if (g_env && g_stdErr)
-	{
-		jbyteArray byteArray = g_env->NewByteArray(len);
-		g_env->SetByteArrayRegion(byteArray, 0, len, (const jbyte *)str);
-		code = callIntMethod(g_env, g_stdErr, "onStdErr", STDERR_SIG, (jlong)callerHandle, byteArray, (jint)len);
-	}
-	return code;
+	GSInstanceData *gsdata = (GSInstanceData *)callerHandle;
+	assert(gsdata);
+
+	if (!gsdata->env || !gsdata->stdErr) return len;
+
+	jbyteArray byteArray = gsdata->env->NewByteArray(len);
+	gsdata->env->SetByteArrayRegion(byteArray, 0, len, (const jbyte *)str);
+
+	jint result = callIntMethod(gsdata->env, gsdata->stdErr, "onStdErr", STDERR_SIG, (jlong)gsdata->stdioHandle, byteArray, (jint)len);
+	if (gsdata->env->ExceptionCheck()) return 0;
+
+	return result;
 }
 
-void callbacks::setPollCallback(jobject poll)
+void callbacks::setPollCallback(GSInstanceData *idata, jobject poll)
 {
-	if (g_env)
+	if (idata->env)
 	{
-		if (g_poll)
-			g_env->DeleteGlobalRef(g_poll);
+		if (idata->poll)
+			idata->env->DeleteGlobalRef(idata->poll);
 
-		g_poll = g_env->NewGlobalRef(poll);
+		idata->poll = idata->env->NewGlobalRef(poll);
 	}
 }
 
 int callbacks::pollFunction(void *callerHandle)
 {
 	int code = 0;
-	if (g_env && g_poll)
+
+	GSInstanceData *gsdata = (GSInstanceData *)callerHandle;
+	assert(gsdata);
+
+	if (gsdata->env && gsdata->poll)
 	{
-		code = callIntMethod(g_env, g_poll, "onPoll", POLL_SIG, (jlong)callerHandle);
+		code = callIntMethod(gsdata->env, gsdata->poll, "onPoll", POLL_SIG, (jlong)gsdata->callerHandle);
 	}
 	return code;
 }
 
-void callbacks::setDisplayCallback(jobject displayCallback)
+void callbacks::setDisplayCallback(GSInstanceData *idata, jobject displayCallback)
 {
-	if (g_env)
+	if (idata->env)
 	{
-		if (g_displayCallback)
+		if (idata->displayCallback)
 		{
-			g_env->DeleteGlobalRef(g_displayCallback);
-			g_displayCallback = NULL;
+			idata->env->DeleteGlobalRef(idata->displayCallback);
+			idata->displayCallback = NULL;
 		}
 
-		g_displayCallback = g_env->NewGlobalRef(displayCallback);
+		idata->displayCallback = idata->env->NewGlobalRef(displayCallback);
 		//g_displayCallback = displayCallback;
 	}
 }
 
-void callbacks::setCalloutCallback(jobject callout)
+void callbacks::setCalloutCallback(GSInstanceData *idata, jobject callout)
 {
-	if (g_env)
+	if (idata->env)
 	{
-		if (g_callout)
-			g_env->DeleteGlobalRef(g_callout);
+		if (idata->callout)
+			idata->env->DeleteGlobalRef(idata->callout);
 
-		g_callout = g_env->NewGlobalRef(callout);
+		idata->callout = idata->env->NewGlobalRef(callout);
 	}
 }
 
 int callbacks::calloutFunction(void *instance, void *handle, const char *deviceName, int id, int size, void *data)
 {
 	int code = 0;
-	if (g_env && g_callout)
+
+	GSInstanceData *gsdata = findDataFromInstance(instance);
+	assert(gsdata);
+
+	if (gsdata->env && gsdata->callout)
 	{
-		jsize len = strlen(deviceName);
-		jbyteArray array = g_env->NewByteArray(len);
-		g_env->SetByteArrayRegion(array, 0, len, (const jbyte *)deviceName);
-		code = callIntMethod(g_env, g_callout, "onCallout", "(JJ[BIIJ)I", (jlong)instance, (jlong)handle, array, id, size, (jlong)data);
+		jsize len = (jsize)strlen(deviceName);
+		jbyteArray array = gsdata->env->NewByteArray(len);
+		gsdata->env->SetByteArrayRegion(array, 0, len, (const jbyte *)deviceName);
+
+		// TODO: gsdata->callerHandle is not consistent with the specification for a callout
+		code = callIntMethod(gsdata->env, gsdata->callout, "onCallout", "(JJ[BIIJ)I", (jlong)instance, (jlong)gsdata->callerHandle, array, id, size, (jlong)data);
 	}
 	return code;
 }
@@ -166,13 +185,17 @@ int callbacks::calloutFunction(void *instance, void *handle, const char *deviceN
 int callbacks::display::displayOpenFunction(void *handle, void *device)
 {
 	int code = 0;
-	if (g_env && g_displayCallback)
+
+	GSInstanceData *gsdata = (GSInstanceData *)handle;
+	assert(gsdata);
+
+	if (gsdata->env && gsdata->displayCallback)
 	{
-		jclass clazz = g_env->GetObjectClass(g_displayCallback);
-		const char *name = getClassName(g_env, clazz);
+		jclass clazz = gsdata->env->GetObjectClass(gsdata->displayCallback);
+		const char *name = getClassName(gsdata->env, clazz);
 		freeClassName(name);
-		code = callIntMethod(g_env, g_displayCallback, "onDisplayOpen", DISPLAY_OPEN_SIG, (jlong)handle, (jlong)device);
-		CHECK_AND_RETURN(g_env);
+		code = callIntMethod(gsdata->env, gsdata->displayCallback, "onDisplayOpen", DISPLAY_OPEN_SIG, (jlong)gsdata->displayHandle, (jlong)device);
+		CHECK_AND_RETURN(gsdata->env);
 	}
 	return code;
 }
@@ -180,10 +203,14 @@ int callbacks::display::displayOpenFunction(void *handle, void *device)
 int callbacks::display::displayPrecloseFunction(void *handle, void *device)
 {
 	int code = 0;
-	if (g_env && g_displayCallback)
+
+	GSInstanceData *gsdata = (GSInstanceData *)handle;
+	assert(gsdata);
+
+	if (gsdata->env && gsdata->displayCallback)
 	{
-		code = callIntMethod(g_env, g_displayCallback, "onDisplayPreclose", DISPLAY_PRECLOSE_SIG, (jlong)handle, (jlong)device);
-		CHECK_AND_RETURN(g_env);
+		code = callIntMethod(gsdata->env, gsdata->displayCallback, "onDisplayPreclose", DISPLAY_PRECLOSE_SIG, (jlong)gsdata->displayHandle, (jlong)device);
+		CHECK_AND_RETURN(gsdata->env);
 	}
 	return code;
 }
@@ -191,10 +218,14 @@ int callbacks::display::displayPrecloseFunction(void *handle, void *device)
 int callbacks::display::displayCloseFunction(void *handle, void *device)
 {
 	int code = 0;
-	if (g_env && g_displayCallback)
+
+	GSInstanceData *gsdata = (GSInstanceData *)handle;
+	assert(gsdata);
+
+	if (gsdata->env && gsdata->displayCallback)
 	{
-		code = callIntMethod(g_env, g_displayCallback, "onDisplayClose", DISPLAY_CLOSE_SIG, (jlong)handle, (jlong)device);
-		CHECK_AND_RETURN(g_env);
+		code = callIntMethod(gsdata->env, gsdata->displayCallback, "onDisplayClose", DISPLAY_CLOSE_SIG, (jlong)gsdata->displayHandle, (jlong)device);
+		CHECK_AND_RETURN(gsdata->env);
 	}
 	return code;
 }
@@ -202,11 +233,15 @@ int callbacks::display::displayCloseFunction(void *handle, void *device)
 int callbacks::display::displayPresizeFunction(void *handle, void *device, int width, int height, int raster, unsigned int format)
 {
 	int code = 0;
-	if (g_env && g_displayCallback)
+
+	GSInstanceData *gsdata = (GSInstanceData *)handle;
+	assert(gsdata);
+
+	if (gsdata->env && gsdata->displayCallback)
 	{
-		code = callIntMethod(g_env, g_displayCallback, "onDisplayPresize", DISPLAY_PRESIZE_SIG, (jlong)handle,
+		code = callIntMethod(gsdata->env, gsdata->displayCallback, "onDisplayPresize", DISPLAY_PRESIZE_SIG, (jlong)gsdata->displayHandle,
 			(jlong)device, width, height, raster, (jint)format);
-		CHECK_AND_RETURN(g_env);
+		CHECK_AND_RETURN(gsdata->env);
 	}
 	return code;
 }
@@ -215,57 +250,61 @@ int callbacks::display::displaySizeFunction(void *handle, void *device, int widt
 	unsigned int format, unsigned char *pimage)
 {
 	int code = 0;
-	if (g_env && g_displayCallback)
+
+	GSInstanceData *gsdata = (GSInstanceData *)handle;
+	assert(gsdata);
+
+	if (gsdata->env && gsdata->displayCallback)
 	{
 		jsize len = height * raster;
-		jbyteArray byteArray = g_env->NewByteArray(len);
-		g_env->SetByteArrayRegion(byteArray, 0, len, (signed char *)pimage);
+		jbyteArray byteArray = gsdata->env->NewByteArray(len);
+		gsdata->env->SetByteArrayRegion(byteArray, 0, len, (signed char *)pimage);
 
 		static const char *const bytePointerClassName = "com/artifex/gsjava/util/BytePointer";
 		static const char *const nativePointerClassName = "com/artifex/gsjava/util/NativePointer";
 
-		jclass bytePointerClass = g_env->FindClass(bytePointerClassName);
+		jclass bytePointerClass = gsdata->env->FindClass(bytePointerClassName);
 		if (bytePointerClass == NULL)
 		{
-			throwNoClassDefError(g_env, bytePointerClassName);
+			throwNoClassDefError(gsdata->env, bytePointerClassName);
 			return -21;
 		}
 
-		jclass nativePointerClass = g_env->FindClass(nativePointerClassName);
+		jclass nativePointerClass = gsdata->env->FindClass(nativePointerClassName);
 		if (nativePointerClass == NULL)
 		{
-			throwNoClassDefError(g_env, nativePointerClassName);
+			throwNoClassDefError(gsdata->env, nativePointerClassName);
 			return -21;
 		}
 
-		jmethodID constructor = g_env->GetMethodID(bytePointerClass, "<init>", "()V");
+		jmethodID constructor = gsdata->env->GetMethodID(bytePointerClass, "<init>", "()V");
 		if (constructor == NULL)
 		{
-			throwNoSuchMethodError(g_env, "com.artifex.gsjava.util.BytePointer.<init>()V");
+			throwNoSuchMethodError(gsdata->env, "com.artifex.gsjava.util.BytePointer.<init>()V");
 			return -21;
 		}
-		jobject bytePointer = g_env->NewObject(bytePointerClass, constructor);
+		jobject bytePointer = gsdata->env->NewObject(bytePointerClass, constructor);
 
-		jfieldID dataPtrID = g_env->GetFieldID(nativePointerClass, "address", "J");
+		jfieldID dataPtrID = gsdata->env->GetFieldID(nativePointerClass, "address", "J");
 		if (dataPtrID == NULL)
 		{
-			throwNoSuchFieldError(g_env, "address");
+			throwNoSuchFieldError(gsdata->env, "address");
 			return -21;
 		}
 
-		jfieldID lengthID = g_env->GetFieldID(bytePointerClass, "length", "J");
+		jfieldID lengthID = gsdata->env->GetFieldID(bytePointerClass, "length", "J");
 		if (lengthID == NULL)
 		{
-			throwNoSuchFieldError(g_env, "length");
+			throwNoSuchFieldError(gsdata->env, "length");
 			return -21;
 		}
 
-		g_env->SetLongField(bytePointer, dataPtrID, (jlong)pimage);
-		g_env->SetLongField(bytePointer, lengthID, len);
+		gsdata->env->SetLongField(bytePointer, dataPtrID, (jlong)pimage);
+		gsdata->env->SetLongField(bytePointer, lengthID, len);
 
-		code = callIntMethod(g_env, g_displayCallback, "onDisplaySize", DISPLAY_SIZE_SIG, (jlong)handle,
+		code = callIntMethod(gsdata->env, gsdata->displayCallback, "onDisplaySize", DISPLAY_SIZE_SIG, (jlong)gsdata->displayHandle,
 			(jlong)device, width, height, raster, (jint)format, bytePointer);
-		CHECK_AND_RETURN(g_env);
+		CHECK_AND_RETURN(gsdata->env);
 	}
 	return code;
 }
@@ -273,10 +312,14 @@ int callbacks::display::displaySizeFunction(void *handle, void *device, int widt
 int callbacks::display::displaySyncFunction(void *handle, void *device)
 {
 	int code = 0;
-	if (g_env && g_displayCallback)
+
+	GSInstanceData *gsdata = (GSInstanceData *)handle;
+	assert(gsdata);
+
+	if (gsdata->env && gsdata->displayCallback)
 	{
-		code = callIntMethod(g_env, g_displayCallback, "onDisplaySync", DISPLAY_SYNC_SIG, (jlong)handle, (jlong)device);
-		CHECK_AND_RETURN(g_env);
+		code = callIntMethod(gsdata->env, gsdata->displayCallback, "onDisplaySync", DISPLAY_SYNC_SIG, (jlong)gsdata->displayHandle, (jlong)device);
+		CHECK_AND_RETURN(gsdata->env);
 	}
 	return code;
 }
@@ -284,11 +327,15 @@ int callbacks::display::displaySyncFunction(void *handle, void *device)
 int callbacks::display::displayPageFunction(void *handle, void *device, int copies, int flush)
 {
 	int code = 0;
-	if (g_env && g_displayCallback)
+
+	GSInstanceData *gsdata = (GSInstanceData *)handle;
+	assert(gsdata);
+
+	if (gsdata->env && gsdata->displayCallback)
 	{
-		code = callIntMethod(g_env, g_displayCallback, "onDisplayPage", DISPLAY_PAGE_SIG, (jlong)handle,
+		code = callIntMethod(gsdata->env, gsdata->displayCallback, "onDisplayPage", DISPLAY_PAGE_SIG, (jlong)gsdata->displayHandle,
 			(jlong)device, copies, flush);
-		CHECK_AND_RETURN(g_env);
+		CHECK_AND_RETURN(gsdata->env);
 	}
 	return code;
 }
@@ -296,11 +343,15 @@ int callbacks::display::displayPageFunction(void *handle, void *device, int copi
 int callbacks::display::displayUpdateFunction(void *handle, void *device, int x, int y, int w, int h)
 {
 	int code = 0;
-	if (g_env && g_displayCallback)
+
+	GSInstanceData *gsdata = (GSInstanceData *)handle;
+	assert(gsdata);
+
+	if (gsdata->env && gsdata->displayCallback)
 	{
-		code = callIntMethod(g_env, g_displayCallback, "onDisplayUpdate", DISPLAY_UPDATE_SIG, (jlong)handle,
+		code = callIntMethod(gsdata->env, gsdata->displayCallback, "onDisplayUpdate", DISPLAY_UPDATE_SIG, (jlong)gsdata->displayHandle,
 			(jlong)device, x, y, w, h);
-		CHECK_AND_RETURN(g_env);
+		CHECK_AND_RETURN(gsdata->env);
 	}
 	return code;
 }
@@ -309,14 +360,18 @@ int callbacks::display::displaySeparationFunction(void *handle, void *device, in
 	unsigned short c, unsigned short m, unsigned short y, unsigned short k)
 {
 	int code = 0;
-	if (g_env && g_displayCallback)
+
+	GSInstanceData *gsdata = (GSInstanceData *)handle;
+	assert(gsdata);
+
+	if (gsdata->env && gsdata->displayCallback)
 	{
-		jsize len = strlen(componentName);
-		jbyteArray byteArray = g_env->NewByteArray(len);
-		g_env->SetByteArrayRegion(byteArray, 0, len, (const jbyte *)componentName);
-		code = callIntMethod(g_env, g_displayCallback, "onDisplaySeparation", DISPLAY_SEPARATION_SIG, (jlong)handle,
+		jsize len = (jsize)strlen(componentName);
+		jbyteArray byteArray = gsdata->env->NewByteArray(len);
+		gsdata->env->SetByteArrayRegion(byteArray, 0, len, (const jbyte *)componentName);
+		code = callIntMethod(gsdata->env, gsdata->displayCallback, "onDisplaySeparation", DISPLAY_SEPARATION_SIG, (jlong)gsdata->displayHandle,
 			(jlong)device, component, byteArray, c, m, y, k);
-		CHECK_AND_RETURN(g_env);
+		CHECK_AND_RETURN(gsdata->env);
 	}
 	return code;
 }
@@ -324,11 +379,15 @@ int callbacks::display::displaySeparationFunction(void *handle, void *device, in
 int callbacks::display::displayAdjustBandHeightFunction(void *handle, void *device, int bandHeight)
 {
 	int code = 0;
-	if (g_env && g_displayCallback)
+
+	GSInstanceData *gsdata = (GSInstanceData *)handle;
+	assert(gsdata);
+
+	if (gsdata->env && gsdata->displayCallback)
 	{
-		code = callIntMethod(g_env, g_displayCallback, "onDisplayAdjustBandHeght", DISPLAY_ADJUST_BAND_HEIGHT_SIG,
-			(jlong)handle, (jlong)device, bandHeight);
-		CHECK_AND_RETURN(g_env);
+		code = callIntMethod(gsdata->env, gsdata->displayCallback, "onDisplayAdjustBandHeght", DISPLAY_ADJUST_BAND_HEIGHT_SIG,
+			(jlong)gsdata->displayHandle, (jlong)device, bandHeight);
+		CHECK_AND_RETURN(gsdata->env);
 	}
 	return code;
 }
@@ -337,20 +396,24 @@ int callbacks::display::displayRectangleRequestFunction(void *handle, void *devi
 	int *raster, int *plane_raster, int *x, int *y, int *w, int *h)
 {
 	int code = 0;
-	if (g_env && g_displayCallback)
+
+	GSInstanceData *gsdata = (GSInstanceData *)handle;
+	assert(gsdata);
+
+	if (gsdata->env && gsdata->displayCallback)
 	{
-		Reference memoryRef = Reference(g_env, toWrapperType(g_env, (jlong)*memory));
-		Reference oxRef = Reference(g_env, toWrapperType(g_env, (jint)*ox));
-		Reference oyRef = Reference(g_env, toWrapperType(g_env, (jint)*oy));
-		Reference rasterRef = Reference(g_env, toWrapperType(g_env, (jint)*raster));
-		Reference planeRasterRef = Reference(g_env, toWrapperType(g_env, (jint)*plane_raster));
-		Reference xRef = Reference(g_env, toWrapperType(g_env, (jint)*x));
-		Reference yRef = Reference(g_env, toWrapperType(g_env, (jint)*y));
-		Reference wRef = Reference(g_env, toWrapperType(g_env, (jint)*w));
-		Reference hRef = Reference(g_env, toWrapperType(g_env, (jint)*h));
-
-		code = callIntMethod(g_env, g_displayCallback, "onDisplayRectangleRequest", DISPLAY_RECTANGLE_REQUEST,
-			(jlong)handle,
+		Reference memoryRef = Reference(gsdata->env, toWrapperType(gsdata->env, (jlong)*memory));
+		Reference oxRef = Reference(gsdata->env, toWrapperType(gsdata->env, (jint)*ox));
+		Reference oyRef = Reference(gsdata->env, toWrapperType(gsdata->env, (jint)*oy));
+		Reference rasterRef = Reference(gsdata->env, toWrapperType(gsdata->env, (jint)*raster));
+		Reference planeRasterRef = Reference(gsdata->env, toWrapperType(gsdata->env, (jint)*plane_raster));
+		Reference xRef = Reference(gsdata->env, toWrapperType(gsdata->env, (jint)*x));
+		Reference yRef = Reference(gsdata->env, toWrapperType(gsdata->env, (jint)*y));
+		Reference wRef = Reference(gsdata->env, toWrapperType(gsdata->env, (jint)*w));
+		Reference hRef = Reference(gsdata->env, toWrapperType(gsdata->env, (jint)*h));
+
+		code = callIntMethod(gsdata->env, gsdata->displayCallback, "onDisplayRectangleRequest", DISPLAY_RECTANGLE_REQUEST,
+			(jlong)gsdata->displayHandle,
 			(jlong)device,
 			memoryRef.object(),
 			oxRef.object(),
@@ -373,7 +436,7 @@ int callbacks::display::displayRectangleRequestFunction(void *handle, void *devi
 		*w = wRef.intValue();
 		*h = hRef.intValue();
 
-		CHECK_AND_RETURN(g_env);
+		CHECK_AND_RETURN(gsdata->env);
 	}
 	return code;
 }
diff --git a/demos/java/jni/gs_jni/callbacks.h b/demos/java/jni/gs_jni/callbacks.h
index 55508f2b..e8a23f93 100644
--- a/demos/java/jni/gs_jni/callbacks.h
+++ b/demos/java/jni/gs_jni/callbacks.h
@@ -2,6 +2,8 @@
 
 #include <jni.h>
 
+#include "instance_data.h"
+
 namespace callbacks
 {
 	/*!
@@ -10,17 +12,17 @@ namespace callbacks
 
 	@param env A JNIEnv.
 	*/
-	void setJNIEnv(JNIEnv *env);
+	void setJNIEnv(GSInstanceData *idata, JNIEnv *env);
 
-	void setIOCallbacks(jobject stdIn, jobject stdOut, jobject stdErr);
+	void setIOCallbacks(GSInstanceData *idata, jobject stdIn, jobject stdOut, jobject stdErr);
 	int stdInFunction(void *callerHandle, char *buf, int len);
 	int stdOutFunction(void *callerHandle, const char *str, int len);
 	int stdErrFunction(void *callerHandle, const char *str, int len);
 
-	void setPollCallback(jobject poll);
+	void setPollCallback(GSInstanceData *idata, jobject poll);
 	int pollFunction(void *callerHandle);
 
-	void setDisplayCallback(jobject displayCallback);
+	void setDisplayCallback(GSInstanceData *idata, jobject displayCallback);
 
 	namespace display
 	{
@@ -49,6 +51,6 @@ namespace callbacks
 			int *x, int *y, int *w, int *h);
 	}
 
-	void setCalloutCallback(jobject calout);
+	void setCalloutCallback(GSInstanceData *idata, jobject callout);
 	int calloutFunction(void *instance, void *handle, const char *deviceName, int id, int size, void *data);
 }
\ No newline at end of file
diff --git a/demos/java/jni/gs_jni/com_artifex_gsjava_GSAPI.cpp b/demos/java/jni/gs_jni/com_artifex_gsjava_GSAPI.cpp
index b28334e9..500f540a 100644
--- a/demos/java/jni/gs_jni/com_artifex_gsjava_GSAPI.cpp
+++ b/demos/java/jni/gs_jni/com_artifex_gsjava_GSAPI.cpp
@@ -4,14 +4,19 @@
 #include <gdevdsp.h>
 #include <string.h>
 #include <memory>
+#include <assert.h>
+#include <string>
 
 #include "jni_util.h"
 #include "callbacks.h"
+#include "instance_data.h"
 
 using namespace util;
 
 static void *getAsPointer(JNIEnv *env, jobject object, gs_set_param_type type, bool *success);
 
+static void storeDispalyHandle(GSInstanceData *idata);
+
 JNIEXPORT jint JNICALL Java_com_artifex_gsjava_GSAPI_gsapi_1revision
 	(JNIEnv *env, jclass, jobject revision, jint len)
 {
@@ -35,54 +40,82 @@ JNIEXPORT jint JNICALL Java_com_artifex_gsjava_GSAPI_gsapi_1new_1instance
 	if (instance == NULL)
 		return throwNullPointerException(env, "LongReference object is NULL");
 
-	void *gsInstance;
-	int code = gsapi_new_instance(&gsInstance, (void *)callerHandle);
+	GSInstanceData *idata = new GSInstanceData();
+	idata->callerHandle = (void *)callerHandle;
+
+	void *gsInstance = NULL;
+	int code = gsapi_new_instance(&gsInstance, idata);
 	if (code == 0)
 		Reference::setValueField(env, instance, toWrapperType(env, (jlong)gsInstance));
+
+	idata->instance = gsInstance;
+
+	putInstanceData(idata);
+
 	return code;
 }
 
 JNIEXPORT void JNICALL Java_com_artifex_gsjava_GSAPI_gsapi_1delete_1instance
 	(JNIEnv *env, jclass, jlong instance)
 {
-	callbacks::setJNIEnv(env);
+	GSInstanceData *idata = findDataFromInstance((void *)instance);
+	assert(idata);
+
+	callbacks::setJNIEnv(idata, env);
 	gsapi_delete_instance((void *)instance);
+
+	deleteDataFromInstance((void *)instance);
 }
 
 JNIEXPORT jint JNICALL Java_com_artifex_gsjava_GSAPI_gsapi_1set_1stdio_1with_1handle
 	(JNIEnv *env, jclass, jlong instance, jobject stdIn, jobject stdOut, jobject stdErr, jlong callerHandle)
 {
+	GSInstanceData *idata = findDataFromInstance((void *)instance);
+	assert(idata);
+
+	idata->stdioHandle = (void *)callerHandle;
+
 	int code = gsapi_set_stdio_with_handle((void *)instance, callbacks::stdInFunction,
-		callbacks::stdOutFunction, callbacks::stdErrFunction, (void *)callerHandle);
+		callbacks::stdOutFunction, callbacks::stdErrFunction, idata);
 	if (code == 0)
 	{
-		callbacks::setJNIEnv(env);
-		callbacks::setIOCallbacks(stdIn, stdOut, stdErr);
+		callbacks::setJNIEnv(idata, env);
+		callbacks::setIOCallbacks(idata, stdIn, stdOut, stdErr);
 	}
+
 	return code;
 }
 
 JNIEXPORT jint JNICALL Java_com_artifex_gsjava_GSAPI_gsapi_1set_1stdio
 	(JNIEnv *env, jclass, jlong instance, jobject stdIn, jobject stdOut, jobject stdErr)
 {
-	int code = gsapi_set_stdio((void *)instance, callbacks::stdInFunction,
-		callbacks::stdOutFunction, callbacks::stdErrFunction);
+	GSInstanceData *idata = findDataFromInstance((void *)instance);
+	assert(idata);
+
+	idata->stdioHandle = NULL;
+
+	int code = gsapi_set_stdio_with_handle((void *)instance, callbacks::stdInFunction,
+		callbacks::stdOutFunction, callbacks::stdErrFunction, idata);
 	if (code == 0)
 	{
-		callbacks::setJNIEnv(env);
-		callbacks::setIOCallbacks(stdIn, stdOut, stdErr);
+		callbacks::setJNIEnv(idata, env);
+		callbacks::setIOCallbacks(idata, stdIn, stdOut, stdErr);
 	}
+
 	return code;
 }
 
 JNIEXPORT jint JNICALL Java_com_artifex_gsjava_GSAPI_gsapi_1set_1poll_1with_1handle
 	(JNIEnv *env, jclass, jlong instance, jobject poll, jlong callerHandle)
 {
+	GSInstanceData *idata = findDataFromInstance((void *)instance);
+	assert(idata);
+
 	int code = gsapi_set_poll_with_handle((void *)instance, callbacks::pollFunction, (void *)callerHandle);
 	if (code == 0)
 	{
-		callbacks::setJNIEnv(env);
-		callbacks::setPollCallback(poll);
+		callbacks::setJNIEnv(idata, env);
+		callbacks::setPollCallback(idata, poll);
 	}
 	return code;
 }
@@ -90,11 +123,14 @@ JNIEXPORT jint JNICALL Java_com_artifex_gsjava_GSAPI_gsapi_1set_1poll_1with_1han
 JNIEXPORT jint JNICALL Java_com_artifex_gsjava_GSAPI_gsapi_1set_1poll
 	(JNIEnv *env, jclass, jlong instance, jobject poll)
 {
+	GSInstanceData *idata = findDataFromInstance((void *)instance);
+	assert(idata);
+
 	int code = gsapi_set_poll((void *)instance, callbacks::pollFunction);
 	if (code == 0)
 	{
-		callbacks::setJNIEnv(env);
-		callbacks::setPollCallback(poll);
+		callbacks::setJNIEnv(idata, env);
+		callbacks::setPollCallback(idata, poll);
 	}
 	return code;
 }
@@ -102,6 +138,12 @@ JNIEXPORT jint JNICALL Java_com_artifex_gsjava_GSAPI_gsapi_1set_1poll
 JNIEXPORT jint JNICALL Java_com_artifex_gsjava_GSAPI_gsapi_1set_1display_1callback
 	(JNIEnv *env, jclass, jlong instance, jobject displayCallback)
 {
+	GSInstanceData *idata = findDataFromInstance((void *)instance);
+	assert(idata);
+
+	if (idata->hasinit && idata->displayCallback)
+		storeDispalyHandle(idata);
+
 	display_callback *cb = new display_callback;
 	cb->size = sizeof(display_callback);
 	cb->version_major = DISPLAY_VERSION_MAJOR;
@@ -124,8 +166,8 @@ JNIEXPORT jint JNICALL Java_com_artifex_gsjava_GSAPI_gsapi_1set_1display_1callba
 	int code = gsapi_set_display_callback((void *)instance, cb);
 	if (code == 0)
 	{
-		callbacks::setJNIEnv(env);
-		callbacks::setDisplayCallback(displayCallback);
+		callbacks::setJNIEnv(idata, env);
+		callbacks::setDisplayCallback(idata, displayCallback);
 	}
 	return code;
 }
@@ -133,11 +175,14 @@ JNIEXPORT jint JNICALL Java_com_artifex_gsjava_GSAPI_gsapi_1set_1display_1callba
 JNIEXPORT jint JNICALL Java_com_artifex_gsjava_GSAPI_gsapi_1register_1callout
 	(JNIEnv *env, jclass, jlong instance, jobject callout, jlong calloutHandle)
 {
+	GSInstanceData *idata = findDataFromInstance((void *)instance);
+	assert(idata);
+
 	int code = gsapi_register_callout((void *)instance, callbacks::calloutFunction, (void *)calloutHandle);
 	if (code == 0)
 	{
-		callbacks::setJNIEnv(env);
-		callbacks::setCalloutCallback(callout);
+		callbacks::setJNIEnv(idata, env);
+		callbacks::setCalloutCallback(idata, callout);
 	}
 	return code;
 }
@@ -157,10 +202,14 @@ JNIEXPORT jint JNICALL Java_com_artifex_gsjava_GSAPI_gsapi_1set_1arg_1encoding
 JNIEXPORT jint JNICALL Java_com_artifex_gsjava_GSAPI_gsapi_1set_1default_1device_1list
 	(JNIEnv *env, jclass, jlong instance, jbyteArray list, jint listlen)
 {
+	GSInstanceData *idata = findDataFromInstance((void *)instance);
+	assert(idata);
+
 	if (list == NULL)
 		return throwNullPointerException(env, "list");
+
 	jboolean isCopy = false;
-	callbacks::setJNIEnv(env);
+	callbacks::setJNIEnv(idata, env);
 	int code = gsapi_set_default_device_list((void *)instance,
 		(const char *)env->GetByteArrayElements(list, &isCopy), listlen);
 	return code;
@@ -190,20 +239,34 @@ JNIEXPORT jint JNICALL Java_com_artifex_gsjava_GSAPI_gsapi_1get_1default_1device
 JNIEXPORT jint JNICALL Java_com_artifex_gsjava_GSAPI_gsapi_1init_1with_1args
 	(JNIEnv *env, jclass, jlong instance, jint argc, jobjectArray argv)
 {
+	GSInstanceData *idata = findDataFromInstance((void *)instance);
+	assert(idata);
+
 	if (argv == NULL)
 		return throwNullPointerException(env, "argv");
+
 	char **cargv = jbyteArray2DToCharArray(env, argv);
-	callbacks::setJNIEnv(env);
+
+	callbacks::setJNIEnv(idata, env);
 	int code = gsapi_init_with_args((void *)instance, argc, cargv);
 	delete2DByteArray(argc, cargv);
+
+	if (code == 0)
+	{
+		idata->hasinit = true;
+		storeDispalyHandle(idata);
+	}
 	return code;
 }
 
 JNIEXPORT jint JNICALL Java_com_artifex_gsjava_GSAPI_gsapi_1run_1string_1begin
 	(JNIEnv *env, jclass, jlong instance, jint userErrors, jobject pExitCode)
 {
+	GSInstanceData *idata = findDataFromInstance((void *)instance);
+	assert(idata);
+
 	int exitCode;
-	callbacks::setJNIEnv(env);
+	callbacks::setJNIEnv(idata, env);
 	int code = gsapi_run_string_begin((void *)instance, userErrors, &exitCode);
 	if (pExitCode)
 		Reference::setValueField(env, pExitCode, toWrapperType(env, (jint)exitCode));
@@ -213,12 +276,16 @@ JNIEXPORT jint JNICALL Java_com_artifex_gsjava_GSAPI_gsapi_1run_1string_1begin
 JNIEXPORT jint JNICALL Java_com_artifex_gsjava_GSAPI_gsapi_1run_1string_1continue
 	(JNIEnv *env, jclass, jlong instance, jbyteArray str, jint length, jint userErrors, jobject pExitCode)
 {
+	GSInstanceData *idata = findDataFromInstance((void *)instance);
+	assert(idata);
+
 	if (str == NULL)
 		return throwNullPointerException(env, "str");
+
 	jboolean copy = false;
 	int exitCode;
 	const char *cstring = (const char *)env->GetByteArrayElements(str, &copy);
-	callbacks::setJNIEnv(env);
+	callbacks::setJNIEnv(idata, env);
 	int code = gsapi_run_string_continue((void *)instance, cstring, length, userErrors, &exitCode);
 	if (pExitCode)
 		Reference::setValueField(env, pExitCode, toWrapperType(env, (jint)exitCode));
@@ -228,8 +295,11 @@ JNIEXPORT jint JNICALL Java_com_artifex_gsjava_GSAPI_gsapi_1run_1string_1continu
 JNIEXPORT jint JNICALL Java_com_artifex_gsjava_GSAPI_gsapi_1run_1string_1end
 	(JNIEnv *env, jclass, jlong instance, jint userErrors, jobject pExitCode)
 {
+	GSInstanceData *idata = findDataFromInstance((void *)instance);
+	assert(idata);
+
 	int exitCode;
-	callbacks::setJNIEnv(env);
+	callbacks::setJNIEnv(idata, env);
 	int code = gsapi_run_string_end((void *)instance, userErrors, &exitCode);
 	if (pExitCode)
 		Reference::setValueField(env, pExitCode, toWrapperType(env, (jint)exitCode));
@@ -239,12 +309,16 @@ JNIEXPORT jint JNICALL Java_com_artifex_gsjava_GSAPI_gsapi_1run_1string_1end
 JNIEXPORT jint JNICALL Java_com_artifex_gsjava_GSAPI_gsapi_1run_1string_1with_1length
 	(JNIEnv *env, jclass, jlong instance, jbyteArray str, jint length, jint userErrors, jobject pExitCode)
 {
+	GSInstanceData *idata = findDataFromInstance((void *)instance);
+	assert(idata);
+
 	if (str == NULL)
 		return throwNullPointerException(env, "str");
+
 	jboolean copy = false;
 	int exitCode;
 	const char *cstring = (const char *)env->GetByteArrayElements(str, &copy);
-	callbacks::setJNIEnv(env);
+	callbacks::setJNIEnv(idata, env);
 	int code = gsapi_run_string_with_length((void *)instance, cstring, length, userErrors, &exitCode);
 	if (pExitCode)
 		Reference::setValueField(env, pExitCode, toWrapperType(env, (jint)exitCode));
@@ -254,12 +328,16 @@ JNIEXPORT jint JNICALL Java_com_artifex_gsjava_GSAPI_gsapi_1run_1string_1with_1l
 JNIEXPORT jint JNICALL Java_com_artifex_gsjava_GSAPI_gsapi_1run_1string
 	(JNIEnv *env, jclass, jlong instance, jbyteArray str, jint userErrors, jobject pExitCode)
 {
+	GSInstanceData *idata = findDataFromInstance((void *)instance);
+	assert(idata);
+
 	if (str == NULL)
 		return throwNullPointerException(env, "str");
+
 	jboolean copy = false;
 	int exitCode;
 	const char *cstring = (const char *)env->GetByteArrayElements(str, &copy);
-	callbacks::setJNIEnv(env);
+	callbacks::setJNIEnv(idata, env);
 	int code = gsapi_run_string((void *)instance, cstring, userErrors, &exitCode);
 	if (pExitCode)
 		Reference::setValueField(env, pExitCode, toWrapperType(env, (jint)exitCode));
@@ -269,12 +347,16 @@ JNIEXPORT jint JNICALL Java_com_artifex_gsjava_GSAPI_gsapi_1run_1string
 JNIEXPORT jint JNICALL Java_com_artifex_gsjava_GSAPI_gsapi_1run_1file
 	(JNIEnv *env, jclass, jlong instance, jbyteArray fileName, jint userErrors, jobject pExitCode)
 {
+	GSInstanceData *idata = findDataFromInstance((void *)instance);
+	assert(idata);
+
 	if (fileName == NULL)
 		return throwNullPointerException(env, "fileName");
+
 	jboolean copy = false;
 	int exitCode;
 	const char *cstring = (const char *)env->GetByteArrayElements(fileName, &copy);
-	callbacks::setJNIEnv(env);
+	callbacks::setJNIEnv(idata, env);
 	int code = gsapi_run_file((void *)instance, cstring, userErrors, &exitCode);
 	if (pExitCode)
 		Reference::setValueField(env, pExitCode, toWrapperType(env, (jint)exitCode));
@@ -290,11 +372,11 @@ JNIEXPORT jint JNICALL Java_com_artifex_gsjava_GSAPI_gsapi_1exit
 JNIEXPORT jint JNICALL Java_com_artifex_gsjava_GSAPI_gsapi_1set_1param
 	(JNIEnv *env, jclass, jlong instance, jbyteArray param, jobject value, jint paramType)
 {
+	GSInstanceData *idata = findDataFromInstance((void *)instance);
+	assert(idata);
+
 	if (!param)
-	{
-		throwNullPointerException(env, "param");
-		return -1;
-	}
+		return throwNullPointerException(env, "param");
 
 	gs_set_param_type type = (gs_set_param_type)paramType;
 	bool paramSuccess;
@@ -308,7 +390,7 @@ JNIEXPORT jint JNICALL Java_com_artifex_gsjava_GSAPI_gsapi_1set_1param
 	jboolean copy = false;
 	const char *cstring = (const char *)env->GetByteArrayElements(param, &copy);
 
-	callbacks::setJNIEnv(env);
+	callbacks::setJNIEnv(idata, env);
 	int code = gsapi_set_param((void *)instance, cstring, data, type);
 	free(data);
 
@@ -355,7 +437,7 @@ JNIEXPORT jint JNICALL Java_com_artifex_gsjava_GSAPI_gsapi_1get_1param_1once
 
 	jbyteArray arr = NULL;
 	const char *str = NULL;
-	int len = 0;
+	jsize len = 0;
 	switch (stripped)
 	{
 	case gs_spt_null:
@@ -382,7 +464,7 @@ JNIEXPORT jint JNICALL Java_com_artifex_gsjava_GSAPI_gsapi_1get_1param_1once
 	case gs_spt_string:
 	case gs_spt_parsed:
 		str = (const char *)data;
-		len = strlen(str) + 1;
+		len = (jsize)strlen(str) + 1;
 		arr = env->NewByteArray(len);
 		env->SetByteArrayRegion(arr, 0, len, (const jbyte *)str);
 		ref.set(arr);
@@ -426,7 +508,7 @@ JNIEXPORT jint JNICALL Java_com_artifex_gsjava_GSAPI_gsapi_1enumerate_1params
 	{
 		iterRef.set((jlong)citer);
 
-		jsize len = strlen(ckey) + 1;
+		jsize len = (jsize)strlen(ckey) + 1;
 		jbyteArray arr = env->NewByteArray(len);
 		env->SetByteArrayRegion(arr, 0, len, (const jbyte *)ckey);
 		keyRef.set(arr);
@@ -507,23 +589,53 @@ void *getAsPointer(JNIEnv *env, jobject object, gs_set_param_type type, bool *su
 		break;
 	case gs_spt_bool:
 		result = malloc(sizeof(int));
+		if (!result)
+		{
+			throwAllocationError(env, "getAsPointer");
+			return NULL;
+		}
+
 		*((int *)result) = (bool)toBoolean(env, object);
 		break;
 	case gs_spt_int:
 		result = malloc(sizeof(int));
+		if (!result)
+		{
+			throwAllocationError(env, "getAsPointer");
+			return NULL;
+		}
+
 		*((int *)result) = (int)toInt(env, object);
 		break;
 	case gs_spt_float:
 		result = malloc(sizeof(float));
+		if (!result)
+		{
+			throwAllocationError(env, "getAsPointer");
+			return NULL;
+		}
+
 		*((float *)result) = (float)toFloat(env, object);
 		break;
 	case gs_spt_long:
 	case gs_spt_i64:
 		result = malloc(sizeof(long long));
+		if (!result)
+		{
+			throwAllocationError(env, "getAsPointer");
+			return NULL;
+		}
+
 		*((long long *)result) = (long long)toLong(env, object);
 		break;
 	case gs_spt_size_t:
 		result = malloc(sizeof(size_t));
+		if (!result)
+		{
+			throwAllocationError(env, "getAsPointer");
+			return NULL;
+		}
+
 		*((size_t *)result) = (size_t)toLong(env, object);
 		break;
 	case gs_spt_name:
@@ -533,6 +645,12 @@ void *getAsPointer(JNIEnv *env, jobject object, gs_set_param_type type, bool *su
 		cstring = (const char *)env->GetByteArrayElements(arr, &copy);
 		len = env->GetArrayLength(arr);
 		result = malloc(sizeof(char) * len);
+		if (!result)
+		{
+			throwAllocationError(env, "getAsPointer");
+			return NULL;
+		}
+
 		//((char *)result)[len - 1] = 0;
 		memcpy(result, cstring, len);
 		break;
@@ -541,6 +659,7 @@ void *getAsPointer(JNIEnv *env, jobject object, gs_set_param_type type, bool *su
 		*success = false;
 		break;
 	}
+
 	if (env->ExceptionCheck())
 	{
 		if (result)
@@ -550,3 +669,51 @@ void *getAsPointer(JNIEnv *env, jobject object, gs_set_param_type type, bool *su
 	}
 	return result;
 }
+
+void storeDispalyHandle(GSInstanceData *idata)
+{
+	static const char PARAM_NAME[] = "DisplayHandle";
+
+	assert(idata);
+	assert(idata->instance);
+
+	char *param = NULL;
+	int bytes = gsapi_get_param(idata->instance, PARAM_NAME, NULL, gs_spt_string);
+	if (bytes == com_artifex_gsjava_GSAPI_GS_ERROR_UNDEFINED)
+		idata->displayCallback = NULL;
+	else
+	{
+		// Parse the DisplayHandle string again
+
+		param = new char[bytes];
+		gsapi_get_param(idata->instance, PARAM_NAME, param, gs_spt_string);
+
+		char *toparse = param;
+
+		int radix = 10; // default base 10
+
+		// If there is a # character, we need to change the radix
+		char *rend = strchr(param, '#');
+		if (rend)
+		{
+			*rend = 0;
+			radix = atoi(param);
+			toparse = rend + 1;
+		}
+
+		char *end;
+		long long val = std::strtoll(toparse, &end, radix);
+
+		idata->displayHandle = (void *)val;
+
+		delete[] param;
+	}
+
+	char buf[20]; // 16#[16 hex digits][null terminator]
+#if defined(_WIN32)
+	sprintf_s(buf, "16#%llx", (long long)idata);
+#else
+    snprintf(buf, sizeof(buf), "16#%llx", (long long)idata);
+#endif
+	gsapi_set_param(idata->instance, PARAM_NAME, buf, gs_spt_string);
+}
diff --git a/demos/java/jni/gs_jni/com_artifex_gsjava_GSAPI.h b/demos/java/jni/gs_jni/com_artifex_gsjava_GSAPI.h
index 68c61e58..fd7e303a 100644
--- a/demos/java/jni/gs_jni/com_artifex_gsjava_GSAPI.h
+++ b/demos/java/jni/gs_jni/com_artifex_gsjava_GSAPI.h
@@ -2,6 +2,8 @@
 #include <jni.h>
 /* Header for class com_artifex_gsjava_GSAPI */
 
+#include "settings.h"
+
 #ifndef _Included_com_artifex_gsjava_GSAPI
 #define _Included_com_artifex_gsjava_GSAPI
 #ifdef __cplusplus
diff --git a/demos/java/jni/gs_jni/com_artifex_gsjava_util_NativePointer.cpp b/demos/java/jni/gs_jni/com_artifex_gsjava_util_NativePointer.cpp
index 04c435cb..0589c6b3 100644
--- a/demos/java/jni/gs_jni/com_artifex_gsjava_util_NativePointer.cpp
+++ b/demos/java/jni/gs_jni/com_artifex_gsjava_util_NativePointer.cpp
@@ -33,8 +33,8 @@ JNIEXPORT void JNICALL Java_com_artifex_gsjava_util_NativePointer_freeNative
 JNIEXPORT jbyteArray JNICALL Java_com_artifex_gsjava_util_NativePointer_byteArrayNative
 (JNIEnv *env, jclass, jlong address, jlong len)
 {
-	jbyteArray array = env->NewByteArray(len);
-	env->SetByteArrayRegion(array, 0, len, (const jbyte *)address);
+	jbyteArray array = env->NewByteArray((jsize)len);
+	env->SetByteArrayRegion(array, 0, (jsize)len, (const jbyte *)address);
 	return array;
 }
 
@@ -53,8 +53,8 @@ JNIEXPORT void JNICALL Java_com_artifex_gsjava_util_NativePointer_setByteNative
 JNIEXPORT jcharArray JNICALL Java_com_artifex_gsjava_util_NativePointer_charArrayNative
 (JNIEnv *env, jclass, jlong address, jlong len)
 {
-	jcharArray array = env->NewCharArray(len);
-	env->SetCharArrayRegion(array, 0, len, (const jchar *)address);
+	jcharArray array = env->NewCharArray((jsize)len);
+	env->SetCharArrayRegion(array, 0, (jsize)len, (const jchar *)address);
 	return array;
 }
 
@@ -73,8 +73,8 @@ JNIEXPORT void JNICALL Java_com_artifex_gsjava_util_NativePointer_setCharNative
 JNIEXPORT jshortArray JNICALL Java_com_artifex_gsjava_util_NativePointer_shortArrayNative
 (JNIEnv *env, jclass, jlong address, jlong len)
 {
-	jshortArray array = env->NewShortArray(len);
-	env->SetShortArrayRegion(array, 0, len, (const jshort *)address);
+	jshortArray array = env->NewShortArray((jsize)len);
+	env->SetShortArrayRegion(array, 0, (jsize)len, (const jshort *)address);
 	return array;
 }
 
@@ -93,8 +93,8 @@ JNIEXPORT void JNICALL Java_com_artifex_gsjava_util_NativePointer_setShortNative
 JNIEXPORT jintArray JNICALL Java_com_artifex_gsjava_util_NativePointer_intArrayNative
 (JNIEnv *env, jclass, jlong address, jlong len)
 {
-	jintArray array = env->NewIntArray(len);
-	env->SetIntArrayRegion(array, 0, len, (const jint *)address);
+	jintArray array = env->NewIntArray((jsize)len);
+	env->SetIntArrayRegion(array, 0, (jsize)len, (const jint *)address);
 	return array;
 }
 
@@ -113,8 +113,8 @@ JNIEXPORT void JNICALL Java_com_artifex_gsjava_util_NativePointer_setIntNative
 JNIEXPORT jlongArray JNICALL Java_com_artifex_gsjava_util_NativePointer_longArrayNative
 (JNIEnv *env, jclass, jlong address, jlong len)
 {
-	jlongArray array = env->NewLongArray(len);
-	env->SetLongArrayRegion(array, 0, len, (const jlong *)address);
+	jlongArray array = env->NewLongArray((jsize)len);
+	env->SetLongArrayRegion(array, 0, (jsize)len, (const jlong *)address);
 	return array;
 }
 
diff --git a/demos/java/jni/gs_jni/com_artifex_gsjava_util_NativePointer.h b/demos/java/jni/gs_jni/com_artifex_gsjava_util_NativePointer.h
index 8dd6a30b..6c053df8 100644
--- a/demos/java/jni/gs_jni/com_artifex_gsjava_util_NativePointer.h
+++ b/demos/java/jni/gs_jni/com_artifex_gsjava_util_NativePointer.h
@@ -2,6 +2,8 @@
 #include <jni.h>
 /* Header for class com_artifex_gsjava_util_NativePointer */
 
+#include "settings.h"
+
 #ifndef _Included_com_artifex_gsjava_util_NativePointer
 #define _Included_com_artifex_gsjava_util_NativePointer
 #ifdef __cplusplus
diff --git a/demos/java/jni/gs_jni/gs_jni.vcxproj b/demos/java/jni/gs_jni/gs_jni.vcxproj
index 5febb0d2..56f03d0a 100644
--- a/demos/java/jni/gs_jni/gs_jni.vcxproj
+++ b/demos/java/jni/gs_jni/gs_jni.vcxproj
@@ -98,7 +98,7 @@
       <GenerateDebugInformation>true</GenerateDebugInformation>
       <EnableUAC>false</EnableUAC>
       <AdditionalDependencies>%(AdditionalDependencies)</AdditionalDependencies>
-      <AdditionalLibraryDirectories>$(SolutionDir)..\..\..\..\debugbin;%(AdditionalLibraryDirectories)</AdditionalLibraryDirectories>
+      <AdditionalLibraryDirectories>$(SolutionDir)..\..\..\..\bin;%(AdditionalLibraryDirectories)</AdditionalLibraryDirectories>
     </Link>
   </ItemDefinitionGroup>
   <ItemDefinitionGroup Condition="'$(Configuration)|$(Platform)'=='Release|Win32'">
@@ -120,6 +120,7 @@
       <OptimizeReferences>true</OptimizeReferences>
       <GenerateDebugInformation>true</GenerateDebugInformation>
       <EnableUAC>false</EnableUAC>
+      <AdditionalLibraryDirectories>$(SolutionDir)..\..\..\..\bin;%(AdditionalLibraryDirectories)</AdditionalLibraryDirectories>
     </Link>
   </ItemDefinitionGroup>
   <ItemDefinitionGroup Condition="'$(Configuration)|$(Platform)'=='Debug|x64'">
@@ -138,7 +139,7 @@
       <GenerateDebugInformation>true</GenerateDebugInformation>
       <EnableUAC>false</EnableUAC>
       <AdditionalDependencies>gpdldll64.lib;%(AdditionalDependencies)</AdditionalDependencies>
-      <AdditionalLibraryDirectories>$(SolutionDir)..\..\..\..\debugbin;%(AdditionalLibraryDirectories)</AdditionalLibraryDirectories>
+      <AdditionalLibraryDirectories>$(SolutionDir)..\..\..\..\bin;%(AdditionalLibraryDirectories)</AdditionalLibraryDirectories>
     </Link>
   </ItemDefinitionGroup>
   <ItemDefinitionGroup Condition="'$(Configuration)|$(Platform)'=='Release|x64'">
@@ -169,13 +170,16 @@
     <ClInclude Include="com_artifex_gsjava_GSAPI.h" />
     <ClInclude Include="com_artifex_gsjava_util_NativePointer.h" />
     <ClInclude Include="framework.h" />
+    <ClInclude Include="instance_data.h" />
     <ClInclude Include="jni_util.h" />
+    <ClInclude Include="settings.h" />
   </ItemGroup>
   <ItemGroup>
     <ClCompile Include="callbacks.cpp" />
     <ClCompile Include="com_artifex_gsjava_GSAPI.cpp" />
     <ClCompile Include="com_artifex_gsjava_util_NativePointer.cpp" />
     <ClCompile Include="dllmain.cpp" />
+    <ClCompile Include="instance_data.cpp" />
     <ClCompile Include="jni_util.cpp" />
   </ItemGroup>
   <Import Project="$(VCTargetsPath)\Microsoft.Cpp.targets" />
diff --git a/demos/java/jni/gs_jni/gs_jni.vcxproj.filters b/demos/java/jni/gs_jni/gs_jni.vcxproj.filters
index 14063f1b..ce1781b7 100644
--- a/demos/java/jni/gs_jni/gs_jni.vcxproj.filters
+++ b/demos/java/jni/gs_jni/gs_jni.vcxproj.filters
@@ -30,6 +30,12 @@
     <ClInclude Include="com_artifex_gsjava_util_NativePointer.h">
       <Filter>Header Files</Filter>
     </ClInclude>
+    <ClInclude Include="instance_data.h">
+      <Filter>Header Files</Filter>
+    </ClInclude>
+    <ClInclude Include="settings.h">
+      <Filter>Header Files</Filter>
+    </ClInclude>
   </ItemGroup>
   <ItemGroup>
     <ClCompile Include="dllmain.cpp">
@@ -47,5 +53,8 @@
     <ClCompile Include="com_artifex_gsjava_util_NativePointer.cpp">
       <Filter>Source Files</Filter>
     </ClCompile>
+    <ClCompile Include="instance_data.cpp">
+      <Filter>Source Files</Filter>
+    </ClCompile>
   </ItemGroup>
 </Project>
\ No newline at end of file
diff --git a/demos/java/jni/gs_jni/install_linux.sh b/demos/java/jni/gs_jni/install_linux.sh
index 1626c212..0f4b1147 100644
--- a/demos/java/jni/gs_jni/install_linux.sh
+++ b/demos/java/jni/gs_jni/install_linux.sh
@@ -1,7 +1,14 @@
 #!bin/bash
 
-echo "Copy libgpdl.so -> /usr/lib/libgpdl.so"
-sudo cp -L "../../../../sobin/libgpdl.so" "/usr/lib/libgpdl.so"
+echo "Copy libgpdl.so"
+cp -L "../jni/gs_jni/gs_jni.so" "gs_jni.so"
 
-echo "Copy gs_jni.so -> /usr/lib/gs_jni.so"
-sudo cp "gs_jni.so" "/usr/lib/gs_jni.so"
\ No newline at end of file
+echo "Create libpgdl.so link"
+cp "../../../sobin/lbgpdl.so" "libgpdl.so"
+
+cd ../../../sobin
+
+echo "Copy libgpdl.so target"
+cp $(readlink "libgpdl.so") "../demos/java/gsviewer"
+
+cd ../demos/java.gsviewer
diff --git a/demos/java/jni/gs_jni/instance_data.cpp b/demos/java/jni/gs_jni/instance_data.cpp
new file mode 100644
index 00000000..a65cdf5e
--- /dev/null
+++ b/demos/java/jni/gs_jni/instance_data.cpp
@@ -0,0 +1,64 @@
+#include "instance_data.h"
+
+#include <unordered_map>
+#include <assert.h>
+#include <mutex>
+
+#if !defined(GSJNI_NO_MT)
+
+static std::unordered_map<void *, GSInstanceData *> g_inst2Data; // instance -> data
+static std::mutex g_mtx;
+
+#else
+
+static GSInstanceData g_global; // Global instance for faster multithreading
+
+#endif
+
+GSInstanceData *putInstanceData(GSInstanceData *data)
+{
+#if !defined(GSJNI_NO_MT)
+	g_mtx.lock();
+
+	assert(g_inst2Data.find(data->instance) == g_inst2Data.end());
+
+	g_inst2Data[data->instance] = data;
+
+	g_mtx.unlock();
+
+	return data;
+
+#else
+	delete data;
+	return &g_global;
+#endif
+}
+
+GSInstanceData *findDataFromInstance(void *instance)
+{
+#if !defined(GSJNI_NO_MT)
+	g_mtx.lock();
+
+	auto it = g_inst2Data.find(instance);
+	GSInstanceData *result = it == g_inst2Data.end() ? NULL : it->second;
+
+	g_mtx.unlock();
+
+	return result;
+#else
+	return &g_global;
+#endif
+}
+
+void deleteDataFromInstance(void *instance)
+{
+#if !defined(GSJNI_NO_MT)
+	g_mtx.lock();
+
+	auto i2dit = g_inst2Data.find(instance);
+	if (i2dit != g_inst2Data.end())
+		g_inst2Data.erase(i2dit);
+
+	g_mtx.unlock();
+#endif
+}
\ No newline at end of file
diff --git a/demos/java/jni/gs_jni/instance_data.h b/demos/java/jni/gs_jni/instance_data.h
new file mode 100644
index 00000000..2b2afe2e
--- /dev/null
+++ b/demos/java/jni/gs_jni/instance_data.h
@@ -0,0 +1,35 @@
+#pragma once
+
+#include <jni.h>
+
+#include "settings.h"
+
+/*
+This class stores data about a Ghostscript instance.
+*/
+class GSInstanceData
+{
+public:
+	void *instance = NULL;			// The Ghostscript instance
+	void *callerHandle = NULL;		// The caller handle passed to gsapi_new_instance
+	void *stdioHandle = NULL;		// The caller handle passed to gsapi_set_stdio_with_handle
+	void *displayHandle = NULL;		// The handle passed to display callbacks
+
+	JNIEnv *env = NULL;				// The JNIEnv which should be used for JNI API calls
+
+	jobject stdIn = NULL;			// The user IStdInFunction class for stdin input
+	jobject stdOut = NULL;			// The user IStdOutFunction class for stdout output
+	jobject stdErr = NULL;			// The user IStdErrFunction class for stderr output
+
+	jobject poll = NULL;			// The user IPollFunction class
+
+	jobject displayCallback = NULL;	// The user DisplayCallback class
+
+	jobject callout = NULL;			// The user ICalloutFunction class
+
+	bool hasinit = false;			// Whether the user has called init_with_args
+};
+
+GSInstanceData *putInstanceData(GSInstanceData *data);
+GSInstanceData *findDataFromInstance(void *instance);
+void deleteDataFromInstance(void *instance);
\ No newline at end of file
diff --git a/demos/java/jni/gs_jni/jni_util.cpp b/demos/java/jni/gs_jni/jni_util.cpp
index 74852a95..cd43c534 100644
--- a/demos/java/jni/gs_jni/jni_util.cpp
+++ b/demos/java/jni/gs_jni/jni_util.cpp
@@ -90,7 +90,7 @@ char **util::jbyteArray2DToCharArray(JNIEnv *env, jobjectArray array)
     {
         jbyteArray byteArrayObject = (jbyteArray)env->GetObjectArrayElement(array, i);
         char *elem = (char *)env->GetByteArrayElements(byteArrayObject, &copy);
-        jsize slen = strlen(elem);
+        jsize slen = (jsize)strlen(elem);
         char *nstring = new char[slen + 1LL];
         nstring[slen] = 0;
         memcpy(nstring, elem, slen);
@@ -145,14 +145,14 @@ jint util::getIntField(JNIEnv *env, jobject object, const char *field)
     return env->GetIntField(object, fieldID);
 }
 
-int util::callIntMethod(JNIEnv *env, jobject object, const char *method, const char *sig, ...)
+jint util::callIntMethod(JNIEnv *env, jobject object, const char *method, const char *sig, ...)
 {
     jmethodID methodID = getMethodID(env, object, method, sig);
     if (methodID == NULL)
         return 0;
 
     va_list args;
-    int result;
+    jint result;
     va_start(args, sig);
     result = env->CallIntMethodV(object, methodID, args);
     va_end(args);
diff --git a/demos/java/jni/gs_jni/jni_util.h b/demos/java/jni/gs_jni/jni_util.h
index 6439712e..2ea20fd4 100644
--- a/demos/java/jni/gs_jni/jni_util.h
+++ b/demos/java/jni/gs_jni/jni_util.h
@@ -2,6 +2,8 @@
 
 #include <jni.h>
 
+#include "settings.h"
+
 #define REFERENCE_VALUE_FILED_NAME "value"
 
 namespace util
@@ -141,7 +143,7 @@ namespace util
 	@param sig The method's signature.
 	@param ... The varargs representing the object's arguments in their respective order.
 	*/
-	int callIntMethod(JNIEnv *env, jobject object, const char *name, const char *sig, ...);
+	jint callIntMethod(JNIEnv *env, jobject object, const char *name, const char *sig, ...);
 
 	void setObjectField(JNIEnv *env, jobject object, const char *field, jobject value);
 
diff --git a/demos/java/jni/gs_jni/settings.h b/demos/java/jni/gs_jni/settings.h
new file mode 100644
index 00000000..9bd7490a
--- /dev/null
+++ b/demos/java/jni/gs_jni/settings.h
@@ -0,0 +1,5 @@
+#pragma once
+
+// Use to disable multithreading support, ghostpdl must be compiled with multithreading
+// enabled as well
+//#define GSJNI_NO_MT
\ No newline at end of file
diff --git a/demos/java/mtdemo/Main.java b/demos/java/mtdemo/Main.java
new file mode 100644
index 00000000..82e63619
--- /dev/null
+++ b/demos/java/mtdemo/Main.java
@@ -0,0 +1,51 @@
+import com.artifex.gsjava.GSInstance;
+
+import java.io.File;
+
+import java.util.Scanner;
+
+public class Main {
+
+	// The file we will read from
+	public static final String INFILE = "../../../examples/tiger.eps";
+
+	// The output directory
+	public static final String OUTDIR = "pdfout";
+
+	public static void main(String[] args) {
+		// For multithreading, call this before any GSInstance objects
+		// are created.
+		GSInstance.setAllowMultithreading(true);
+
+		// Parse first command line argument as thread count
+		int workerCount = 10;
+		if (args.length > 0) {
+			try {
+				workerCount = Integer.parseInt(args[0]);
+			} catch (NumberFormatException e) { }
+		}
+
+		// Create output directory if it doesn't exist
+		File outdirFile = new File(OUTDIR);
+		if (outdirFile.exists()) {
+			if (outdirFile.isFile())
+				System.err.println("Output directory exists as a file!");
+		} else {
+			outdirFile.mkdirs();
+		}
+
+
+		Worker[] workers = new Worker[workerCount];
+
+		// Create each worker
+		for (int i = 0; i < workers.length; i++) {
+			workers[i] = new Worker(INFILE, OUTDIR + "/out" + i + ".pdf");
+		}
+
+		// Dispatch each worker
+		System.out.println("Starting workers...");
+		for (int i = 0; i < workers.length; i++) {
+			workers[i].start();
+		}
+	}
+}
diff --git a/demos/java/mtdemo/README.txt b/demos/java/mtdemo/README.txt
new file mode 100644
index 00000000..0dca6335
--- /dev/null
+++ b/demos/java/mtdemo/README.txt
@@ -0,0 +1,53 @@
+This directory contains files which demo multithreading in Ghostscript
+using the Java Language Bindings. The application here simply reads in
+the same EPS file and outputs it to multiple PDF files on different
+threads.
+
+What is here?
+
+* Main.java - Class containing Java main method
+* Worker.java - Class which handles concurrently running Ghostscript
+* build_darwin.sh - Builds the Java program on Darwin systems
+* build_linux.sh - Builds the Java program on Linux systems
+* build_win32.bat - Builds the Java program on Windows
+* runmtd_darwin.sh - Runs the Java program on Darwin systems
+* runmtd_linux.sh - Runs the Java program on Linux systems
+* runmtd_win32.bat - Starts the Java program for Windows
+
+Build/run instructions:
+
+-= WINDOWS =-
+
+1. Ensure the following libraries have been built and are in
+   this directory:
+	* gpdldll64.dll
+	* gs_jni.dll
+
+2. Run build_win32.bat to build.
+
+3. Run runmtd_win32.bat to start the application.
+
+
+-= LINUX =-
+
+1. Ensure the following libraries have been built and are in
+   this directory:
+	* libgpdl.so (this would have been built as a link to another file, so
+	  it should be copied into this directory and renamed to libgpdl.so)
+	  gs_jni.so
+
+2. If using OpenJDK 8, the property "assistive_technologies" may
+   need to be modified for the Java code to build. It can be modified by
+   editing the "accessibility.properties" file. This is located at:
+
+   /etc/java-8-openjdk/accessibility.properties
+
+3. Run build_linux.sh to build and copy libraries.
+
+5. Run runmtd_linux.sh to start the application.
+
+
+-= DARWIN =-
+
+Same as Linux, except with .dylib extensions on all shared objects and
+"_darwin.sh" suffixes instead of "_linux.sh".
\ No newline at end of file
diff --git a/demos/java/mtdemo/Worker.java b/demos/java/mtdemo/Worker.java
new file mode 100644
index 00000000..53393cba
--- /dev/null
+++ b/demos/java/mtdemo/Worker.java
@@ -0,0 +1,127 @@
+import java.io.File;
+
+import com.artifex.gsjava.GSInstance;
+import com.artifex.gsjava.callbacks.DisplayCallback;
+import com.artifex.gsjava.util.*;
+import com.artifex.gsjava.callbacks.*;
+
+import java.io.IOException;
+
+import java.util.Arrays;
+
+import static com.artifex.gsjava.GSAPI.*;
+
+/**
+ * Handles running a separate instance of Ghostscript.
+ */
+public class Worker implements Runnable {
+
+	// Whether to use Java-implemented standard input/output
+	public static final boolean USE_CUSTOM_STDIO = true;
+
+	// Whether stdout is enabled (effective only if USE_CUSTOM_STDIO = true)
+	public static final boolean USE_STDOUT = false;
+
+	private static int ID = 0; // Next thread ID
+
+	private final File inPS, outPDF;	// Input and output files
+	private final Thread thread;		// The thread running this worker
+
+	/**
+	 * Create a worker thread to convert a postscript file
+	 * to a pdf file.
+	 *
+	 * @param inPS The postscript file.
+	 * @param outPDF The output PDF file.
+	 */
+	public Worker(String inPS, String outPDF) {
+		this.inPS = new File(inPS);
+		this.outPDF = new File(outPDF);
+		this.thread = new Thread(this);
+		this.thread.setName("Worker-" + ID++);
+	}
+
+	/**
+	 * Starts this worker
+	 */
+	public void start() {
+		System.out.println("Start: " + thread.getName());
+		thread.start();
+	}
+
+	@Override
+	public void run() {
+		System.out.println("Started worker: " + thread.getName());
+
+		GSInstance gsInstance = null;
+		try {
+			gsInstance = createGSInstance();
+
+			// If we want to use the IO functions StdIO, set them
+			if (USE_CUSTOM_STDIO) {
+				StdIO io = new StdIO();
+				gsInstance.set_stdio(io, USE_STDOUT ? io : null, io);
+			}
+
+			// Create the output file if it doesn't exist
+			if (!outPDF.exists())
+				outPDF.createNewFile();
+
+			// Ghostscript arguments to use with init_with_args
+			String[] args = {
+				"gs",
+				"-sDEVICE=pdfwrite",
+				"-o", outPDF.getPath(),
+				inPS.getPath()
+			};
+
+			// init_with_args will perform all the conversions
+			int code = gsInstance.init_with_args(args);
+			if (code != GS_ERROR_OK)
+				throw new IllegalStateException("Failed to init with args (code = " + code + ")");
+
+			System.out.println("Worker " + thread.getName() + " completed.");
+		} catch (Exception e) {
+			System.err.println("Worker " + thread.getName() + " threw exception: " + e);
+		} finally {
+			if (gsInstance != null)
+				gsInstance.delete_instance();
+		}
+	}
+
+	// Creates a new Ghostscript inistance
+	private GSInstance createGSInstance() {
+		GSInstance gsInstance = new GSInstance();
+
+		int code;
+		code = gsInstance.set_arg_encoding(1);
+		if (code != GS_ERROR_OK) {
+			gsInstance.delete_instance();
+			throw new IllegalStateException("Failed to set arg encoding (code = " + code + ")");
+		}
+
+		return gsInstance;
+	}
+
+	// Handles standard input/output
+	private static class StdIO implements IStdOutFunction, IStdErrFunction, IStdInFunction {
+
+		public int onStdOut(long callerHandle, byte[] str, int len) {
+			System.out.println(new String(str));
+			return len;
+		}
+
+		public int onStdErr(long callerHandle, byte[] str, int len) {
+			System.err.println(new String(str));
+			return len;
+		}
+
+		public int onStdIn(long callerHandle, byte[] buf, int len) {
+			try {
+				return System.in.read(buf, 0, len);
+			} catch (IOException e) {
+				return 0;
+			}
+		}
+	}
+}
diff --git a/demos/java/mtdemo/build_darwin.sh b/demos/java/mtdemo/build_darwin.sh
new file mode 100755
index 00000000..6080bed0
--- /dev/null
+++ b/demos/java/mtdemo/build_darwin.sh
@@ -0,0 +1,28 @@
+#!/bin/bash
+
+echo "Build mtdemo"
+
+cd ../gsjava
+
+bash build_darwin.sh
+
+cd ../mtdemo
+
+cp ../mtdemo/gsjava.jar gsjava.jar
+
+echo "Compiling mtdemo Java source..."
+javac -classpath "../gsjava/bin:." "Main.java" "Worker.java"
+echo "Done."
+
+echo "Copy gs_jni.dylib"
+cp "../jni/gs_jni/gs_jni.dylib" "gs_jni.dylib"
+
+echo "Create libgpdl.dylib link"
+cp "../../../sobin/libgpdl.dylib" "libgpdl.dylib"
+
+cd ../../../sobin
+
+echo "Copy libgpdl.dylib target"
+cp $(readlink "libgpdl.dylib") "../demos/java/mtdemo"
+
+cd ../demos/java/mtdemo
\ No newline at end of file
diff --git a/demos/java/mtdemo/build_linux.sh b/demos/java/mtdemo/build_linux.sh
new file mode 100755
index 00000000..698b4583
--- /dev/null
+++ b/demos/java/mtdemo/build_linux.sh
@@ -0,0 +1,28 @@
+#!/bin/bash
+
+echo "Build mtdemo"
+
+cd ../gsjava
+
+bash build_linux.sh
+
+cd ../mtdemo
+
+cp ../gsjava/gsjava.jar gsjava.jar
+
+echo "Compiling mtdemo Java source..."
+javac -classpath "../gsjava/bin:." "Main.java" "Worker.java"
+echo "Done."
+
+echo "Copy gs_jni.so"
+cp "../jni/gs_jni/gs_jni.so" "gs_jni.so"
+
+echo "Create libgpdl.so link"
+cp "../../../sobin/libgpdl.so" "libgpdl.so"
+
+cd ../../../sobin
+
+echo "Copy libgpdl.so target"
+cp $(readlink "libgpdl.so") "../demos/java/mtdemo"
+
+cd ../demos/java/mtdemo
\ No newline at end of file
diff --git a/demos/java/mtdemo/build_win32.bat b/demos/java/mtdemo/build_win32.bat
new file mode 100755
index 00000000..1074fab8
--- /dev/null
+++ b/demos/java/mtdemo/build_win32.bat
@@ -0,0 +1,15 @@
+@echo off
+
+echo Build mtdemo
+
+cd "..\gsjava"
+
+call build_win32
+
+cd "..\mtdemo"
+
+copy "..\gsjava\gsjava.jar" ".\gsjava.jar"
+
+echo Compiling mtdemo Java source...
+javac -cp ../gsjava/bin;. Main.java Worker.java
+echo Done.
\ No newline at end of file
diff --git a/demos/java/mtdemo/runmtd_darwin.sh b/demos/java/mtdemo/runmtd_darwin.sh
new file mode 100755
index 00000000..4e3b2114
--- /dev/null
+++ b/demos/java/mtdemo/runmtd_darwin.sh
@@ -0,0 +1,5 @@
+#!/bin/bash
+
+export LD_PRELOAD=./libgpdl.dylib
+
+java -cp "gsjava.jar:." Main "$ARG1"
diff --git a/demos/java/mtdemo/runmtd_linux.sh b/demos/java/mtdemo/runmtd_linux.sh
new file mode 100755
index 00000000..72acf6b6
--- /dev/null
+++ b/demos/java/mtdemo/runmtd_linux.sh
@@ -0,0 +1,3 @@
+#!/bin/bash
+
+java -cp "gsjava.jar:." Main "$ARG1"
diff --git a/demos/java/mtdemo/runmtd_win32.bat b/demos/java/mtdemo/runmtd_win32.bat
new file mode 100755
index 00000000..f23ce990
--- /dev/null
+++ b/demos/java/mtdemo/runmtd_win32.bat
@@ -0,0 +1,3 @@
+@echo off
+
+java -cp gsjava.jar;. Main %1
\ No newline at end of file
diff --git a/demos/python/examples.py b/demos/python/examples.py
index d5c8b6ad..864bed96 100755
--- a/demos/python/examples.py
+++ b/demos/python/examples.py
@@ -127,7 +127,6 @@ def trans_ps():
 # Run string to feed chunks
 def run_string():
 
-    f = None
     size = 1024;
     in_filename = '%s/examples/tiger.eps' % ghostpdl_root
     out_filename = 'tiger_byte_fed.png'
@@ -139,19 +138,21 @@ def run_string():
     gsapi.gsapi_set_arg_encoding(instance, gsapi.GS_ARG_ENCODING_UTF8)
     gsapi.gsapi_init_with_args(instance, params)
 
-    exitcode = gsapi.gsapi_run_string_begin(instance, 0)
+    gsapi.gsapi_run_string_begin(instance, 0)
 
     with open(in_filename,"rb") as f:
         while True:
             data = f.read(size)
             if not data:
                 break
-            exitcode = gsapi.gsapi_run_string_continue(instance, data, 0)
+            gsapi.gsapi_run_string_continue(instance, data, 0)
 
     exitcode = gsapi.gsapi_run_string_end(instance, 0)
 
     end_gpdl(instance)
 
+    return exitcode
+
 
 # Examples
 print('***********Text extraction***********');
diff --git a/demos/python/gsapi.py b/demos/python/gsapi.py
index 6dfeb95b..4d405a5e 100755
--- a/demos/python/gsapi.py
+++ b/demos/python/gsapi.py
@@ -343,6 +343,7 @@ def gsapi_set_arg_encoding(instance, encoding):
             GS_ARG_ENCODING_UTF8,
             GS_ARG_ENCODING_UTF16LE,
             )
+    global _encoding
     e = _libgs.gsapi_set_arg_encoding(instance, encoding)
     if e < 0:
         raise GSError(e)
@@ -377,7 +378,7 @@ def gsapi_init_with_args(instance, args):
         raise GSError(e)
 
 
-def gsapi_run_string_begin(instance, user_errors):
+def gsapi_run_string_begin(instance, user_errors=0):
     '''
     Returns <exit_code>.
     '''
@@ -388,7 +389,7 @@ def gsapi_run_string_begin(instance, user_errors):
     return pexit_code.value
 
 
-def gsapi_run_string_continue(instance, str_, user_errors):
+def gsapi_run_string_continue(instance, str_, user_errors=0):
     '''
     <str_> should be either a python string or a bytes object. If the former,
     it is converted into a bytes object using utf-8 encoding.
@@ -416,7 +417,7 @@ def gsapi_run_string_continue(instance, str_, user_errors):
     return pexit_code.value
 
 
-def gsapi_run_string_end(instance, user_errors):
+def gsapi_run_string_end(instance, user_errors=0):
     '''
     Returns <exit_code>.
     '''
@@ -431,17 +432,17 @@ def gsapi_run_string_end(instance, user_errors):
     return pexit_code.value
 
 
-def gsapi_run_string_with_length(instance, str_, length, user_errors):
+def gsapi_run_string_with_length(instance, str_, length, user_errors=0):
     '''
     <str_> should be either a python string or a bytes object. If the former,
     it is converted into a bytes object using utf-8 encoding.
 
     Returns <exit_code>.
     '''
-    return gsapi_run_string(instance, str_[:length], user_errors)
+    return gsapi_run_string(instance, str_[:length], user_errors=0)
 
 
-def gsapi_run_string(instance, str_, user_errors):
+def gsapi_run_string(instance, str_, user_errors=0):
     '''
     <str_> should be either a python string or a bytes object. If the former,
     it is converted into a bytes object using utf-8 encoding.
@@ -465,7 +466,7 @@ def gsapi_run_string(instance, str_, user_errors):
     return pexit_code.value
 
 
-def gsapi_run_file(instance, filename, user_errors):
+def gsapi_run_file(instance, filename, user_errors=0):
     '''
     Returns <exit_code>.
     '''
@@ -558,8 +559,7 @@ def gsapi_set_param(instance, param, value, type_=None):
 
     if type_ is None:
         # Choose a gs_spt_* that matches the Python type of <value>.
-        if 0: pass
-        elif value is None:
+        if value is None:
             type_ = gs_spt_null
         elif isinstance(value, bool):
             type_ = gs_spt_bool
@@ -589,8 +589,7 @@ def gsapi_set_param(instance, param, value, type_=None):
     else:
         # Bool/int/float.
         type2 = None
-        if 0: pass
-        elif type_ == gs_spt_bool:
+        if type_ == gs_spt_bool:
             type2 = ctypes.c_int
         elif type_ == gs_spt_int:
             type2 = ctypes.c_int
@@ -977,7 +976,7 @@ if 0:
     #   gsapi_add_fs()
     #   gsapi_remove_fs()
     #
-    class gsapi_fs_t(ctypes.Structure):
+    class gsapi_fs_t(ctypes.Structure): # lgtm [py/unreachable-statement]
         _fields_ = [
                 ('open_file',
                         ctypes.CFUNCTYPE(ctypes.c_int,
@@ -1104,7 +1103,6 @@ if __name__ == '__main__':
         pass
     else:
         assert 0
-    if 0: assert gsapi_get_param(instance, "foo") is None
 
     # Enumerate all params and print name/value.
     print('gsapi_enumerate_params():')