From fa942450e3b289057881a60fd98a9d4b35d99604 Mon Sep 17 00:00:00 2001
From: Kerin Millar <kfm@plushkava.net>
Date: Fri, 7 Jun 2024 14:00:01 +0100
Subject: Add the get_nprocs() function

It stands a good chance of printing a useful value, even in the case
that nproc(1) from coreutils is unavailable.

Signed-off-by: Kerin Millar <kfm@plushkava.net>
---
 functions.sh   | 20 ++++++++++++++++++++
 test-functions | 12 ++++++++++++
 2 files changed, 32 insertions(+)

diff --git a/functions.sh b/functions.sh
index 504ee9e..60a4b2e 100644
--- a/functions.sh
+++ b/functions.sh
@@ -460,6 +460,26 @@ newest()
 	_select_by_mtime -r "$@"
 }
 
+#
+# Tries to determine the number of available processors. Falls back to trying to
+# determine the number of online processors in a way that is somewhat portable.
+#
+get_nprocs()
+{
+	if nproc 2>/dev/null; then
+		# The nproc(1) utility is provided by GNU coreutils. It has the
+		# advantage of acknowledging the effect of sched_setaffinity(2).
+		true
+	elif getconf _NPROCESSORS_ONLN 2>/dev/null; then
+		# This is a non-standard extension. Nevertheless, it works for
+		# glibc, musl-utils, macOS, FreeBSD, NetBSD and OpenBSD.
+		true
+	else
+		warn "get_nprocs: failed to determine the number of processors"
+		false
+	fi
+}
+
 #
 # Considers one or more pathnames and prints the one having the oldest
 # modification time. If at least one parameter is provided, all parameters shall
diff --git a/test-functions b/test-functions
index 813d524..c734141 100755
--- a/test-functions
+++ b/test-functions
@@ -544,6 +544,17 @@ test_whenceforth() {
 	iterate_tests 4 "$@"
 }
 
+test_get_nprocs() {
+	set -- eq 0
+
+	callback() {
+		shift
+		test_description="get_nprocs"
+		nproc=$(get_nprocs) && is_int "${nproc}" && test "${nproc}" -gt 0
+	}
+
+	iterate_tests 2 "$@"
+}
 
 iterate_tests() {
 	slice_width=$1
@@ -610,6 +621,7 @@ test_newest || rc=1
 test_trim || rc=1
 test_hr || rc=1
 test_whenceforth || rc=1
+test_get_nprocs || rc=1
 
 cleanup_tmpdir
 
-- 
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