--- a/gcc/lock-and-run.sh	Thu Oct 25 07:37:49 2018 +0900
+++ b/gcc/lock-and-run.sh	Thu Feb 13 11:34:05 2020 +0900
@@ -1,33 +1,50 @@
 #! /bin/sh
-# Shell-based mutex using mkdir.
+# Shell-based mutex using mkdir.  This script is used in make to prefer
+# serialized execution to avoid consuming too much RAM.  If reusing it,
+# bear in mind that the lock-breaking logic is not race-free, so disable
+# it in err() if concurrent execution could cause more serious problems.
 
+self=`basename $0`
 lockdir="$1" prog="$2"; shift 2 || exit 1
 
 # Remember when we started trying to acquire the lock.
 count=0
-touch lock-stamp.$$
+
+err () {
+    if test -f $lockdir/lock-$1.$$; then
+	rm -rf $lockdir
+	echo "$self: *** (PID $$) removed stale $lockdir" >&2
 
-trap 'rm -r "$lockdir" lock-stamp.$$' 0
+	# Possible variant for uses where races are more problematic:
+	#echo "$self: *** (PID $$) giving up, maybe rm -r $lockdir" >&2
+	#exit 42
+    else
+	touch $lockdir/lock-$1.$$
+    fi
+}
 
 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"
+	# Check for valid lock.
+	if pid=`cat $lockdir/pid 2>/dev/null` && kill -0 $pid 2>/dev/null; then
+	    echo "$self: (PID $$) waiting $count sec to acquire $lockdir from PID $pid" >&2
+	elif test -z "$pid"; then
+	    echo "$self: (PID $$) cannot read $lockdir/pid" >&2
+	    err nopid
 	else
-	    echo waiting to acquire $lockdir >&2
+	    echo "$self: (PID $$) cannot signal $lockdir owner PID $pid" >&2
+	    err dead
 	fi
     fi
     sleep 1
     count=`expr $count + 1`
 done
 
+trap 'rm -rf "$lockdir"' 0
+echo $$ > $lockdir/pidT && mv $lockdir/pidT $lockdir/pid
+echo "$self: (PID $$) acquired $lockdir after $count seconds" >&2
+
 echo $prog "$@"
 $prog "$@"