Add the parallel_run() function

Here is an example of how to use it.

$ parallel_run 0 sha256sum dir/*

Simple commands of a greater level of sophistication can easily be
composed with the aid of functions.

$ sm3sum() { cksum -a sm3 "$@"; }
$ parallel_run 0 sm3sum dir/*

Signed-off-by: Kerin Millar <kfm@plushkava.net>

2 files changed, 64 insertions, 1 deletions

diff --git a/functions.sh b/functions.sh
index 60a4b2e..e849541 100644
--- a/functions.sh
+++ b/functions.sh
@@ -496,6 +496,50 @@ oldest()
 }
 
 #
+# Executes a simple command in parallel. At least two parameters are expected.
+# The first parameter shall be taken as the maximum number of jobs to run
+# concurrently. If specified as less than or equal to 0, the number shall be
+# determined by running the nproc function. The second parameter shall be taken
+# as a command name. The remaining parameters shall be conveyed to the specified
+# command, one at a time. Should at least one command fail, the return value
+# shall be greater than 0.
+#
+parallel_run()
+{
+	local arg cmd i statedir w workers
+
+	if [ "$#" -lt 3 ]; then
+		warn "parallel_run: too few arguments (got $#, expected at least 3)"
+		return 1
+	elif ! is_int "$1"; then
+		_warn_for_args parallel_run "$1"
+		return 1
+	elif [ "$1" -le 0 ] && ! workers=$(get_nprocs); then
+		return 1
+	elif ! statedir=${TMPDIR:-/tmp}/parallel_run.$$.$(srandom); then
+		return 1
+	fi
+	workers=${workers:-$1} cmd=$2
+	shift 2
+	w=0
+	i=0
+	(
+		while [ "$(( w += 1 ))" -le "${workers}" ]; do
+			i=$w
+			while [ "$i" -le "$#" ]; do
+				eval "arg=\$${i}"
+				if ! "${cmd}" "${arg}"; then
+					mkdir -p -- "${statedir}"
+				fi
+				i=$(( i + workers ))
+			done &
+		done
+		wait
+	)
+	! rmdir -- "${statedir}" 2>/dev/null
+}
+
+#
 # Declare the vebegin, veerror, veindent, veinfo, veinfon, veoutdent and vewarn
 # functions. These differ from their non-v-prefixed counterparts in that they
 # only have an effect where EINFO_VERBOSE is true.
diff --git a/test-functions b/test-functions
index c734141..ed3da42 100755
--- a/test-functions
+++ b/test-functions
@@ -556,6 +556,25 @@ test_get_nprocs() {
 	iterate_tests 2 "$@"
 }
 
+test_parallel_run() {
+	set -- \
+		ge  1  N/A                     N/A                     \
+		eq  0  /                       N/A                     \
+		ge  1  /var/empty/nonexistent  N/A                     \
+		eq  0  /                       /                       \
+		ge  1  /                       /var/empty/nonexistent  \
+		ge  1  /var/empty/nonexistent  /var/empty/nonexistent  \
+		ge  1  /var/empty/nonexistent  /
+
+	callback() {
+		shift
+		test_description="parallel_run $(_print_args 0 ls "$@")"
+		parallel_run 0 ls "$@" >/dev/null 2>&1
+	}
+
+	iterate_tests 4 "$@"
+}
+
 iterate_tests() {
 	slice_width=$1
 	shift
@@ -621,7 +640,7 @@ test_newest || rc=1
 test_trim || rc=1
 test_hr || rc=1
 test_whenceforth || rc=1
-test_get_nprocs || rc=1
+test_parallel_run || rc=1
 
 cleanup_tmpdir