only allow a single instance of solaar to run at a time

lib/solaar/gtk.py

@@ -122,8 +122,41 @@ def main():
 	_require('gi.repository', 'python-gi')
 	_require('gi.repository.Gtk', 'gir1.2-gtk-3.0')
 	args = _parse_arguments()
-	_run(args)
 
+	# ensure no more than a single instance runs at a time
+	import os.path as _path
+	import os as _os
+	lock_fd = None
+	for p in _os.environ.get('XDG_RUNTIME_DIR'), '/run/lock', '/var/lock', _os.environ.get('TMPDIR', '/tmp'):
+		if p and _path.isdir(p) and _os.access(p, _os.W_OK):
+			lock_path = _path.join(p, 'solaar.single-instance.%d' % _os.getuid())
+			try:
+				lock_fd = open(lock_path, 'wb')
+				# print ("Single instance lock file is %s" % lock_path)
+				break
+			except:
+				pass
+
+	if lock_fd:
+		import fcntl as _fcntl
+		try:
+			_fcntl.flock(lock_fd, _fcntl.LOCK_EX | _fcntl.LOCK_NB)
+		except IOError as e:
+			if e.errno == 11:
+				import sys
+				sys.exit("solaar: error: Solaar is already running.")
+			else:
+				raise
+	else:
+		import sys
+		print ("solaar: warning: failed to create single instance lock file, ignoring.", file=sys.stderr)
+
+	try:
+		_run(args)
+	finally:
+		if lock_fd:
+			_fcntl.flock(lock_fd, _fcntl.LOCK_UN)
+			lock_fd.close()
 
 if __name__ == '__main__':
 	main()