From 47ed8b7b170e2fcbb8e9326bdb527bf80e5097e2 Mon Sep 17 00:00:00 2001
From: Matthias Kruk <m@m10k.eu>
Date: Sun, 21 Mar 2021 08:49:59 +0900
Subject: [PATCH] include/mutex: Add symlink-based mutex implementation

Scripts that access shared resources need a means to synchronize accesses
to those resources. This commit adds a symlink-based mutex implementation
that can be used for this purpose.
---
 include/mutex.sh | 55 ++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 55 insertions(+)
 create mode 100644 include/mutex.sh

diff --git a/include/mutex.sh b/include/mutex.sh
new file mode 100644
index 0000000..5760cfd
--- /dev/null
+++ b/include/mutex.sh
@@ -0,0 +1,55 @@
+#!/bin/bash
+
+#
+# mutex - pthreads-like mutex implementation for bash scripts
+# Copyright (C) 2021 - Matthias Kruk <m@m10k.eu>
+#
+
+__init() {
+	return 0
+}
+
+mutex_trylock() {
+	local lock
+
+	lock="$1"
+
+	if ! ln -s "$$" "$lock" &> /dev/null; then
+		return 1
+	fi
+
+	return 0
+}
+
+mutex_lock() {
+	local lock
+
+	lock="$1"
+
+	while ! mutex_trylock "$lock"; do
+		sleep 1
+	done
+
+	return 0
+}
+
+mutex_unlock() {
+	local lock
+	local owner
+
+	lock="$1"
+
+	if ! owner=$(readlink "$lock" 2> /dev/null); then
+		return 1
+	fi
+
+	if [ "$owner" -ne "$$" ]; then
+		return 2
+	fi
+
+	if ! rm -f "$lock"; then
+		return 3
+	fi
+
+	return 0
+}
-- 
2.47.3