--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/gcc/lock-and-run.sh	Fri Oct 27 22:46:09 2017 +0900
@@ -0,0 +1,34 @@
+#! /bin/sh
+# Shell-based mutex using mkdir.
+
+lockdir="$1" prog="$2"; shift 2 || exit 1
+
+# Remember when we started trying to acquire the lock.
+count=0
+touch lock-stamp.$$
+
+trap 'rm -r "$lockdir" lock-stamp.$$' 0
+
+until mkdir "$lockdir" 2>/dev/null; do
+    # Say something periodically so the user knows what's up.
+    if [ `expr $count % 30` = 0 ]; then
+	# Reset if the lock has been renewed.
+	if [ -n "`find \"$lockdir\" -newer lock-stamp.$$`" ]; then
+	    touch lock-stamp.$$
+	    count=1
+	# Steal the lock after 5 minutes.
+	elif [ $count = 300 ]; then
+	    echo removing stale $lockdir >&2
+	    rm -r "$lockdir"
+	else
+	    echo waiting to acquire $lockdir >&2
+	fi
+    fi
+    sleep 1
+    count=`expr $count + 1`
+done
+
+echo $prog "$@"
+$prog "$@"
+
+# The trap runs on exit.