From 93dabf8b599d3f1563e6dc9dea0da8496ca15d2d Mon Sep 17 00:00:00 2001
From: "Gudmundur D. Haraldsson" <gudmundur.haraldsson@automattic.com>
Date: Wed, 13 Sep 2023 17:51:38 +0000
Subject: [PATCH] Updating lock file mechanism to be safer

---
 tools-init.sh | 27 +++++++++++++++++++++++++--
 1 file changed, 25 insertions(+), 2 deletions(-)

diff --git a/tools-init.sh b/tools-init.sh
index de69bfea..40f40ad2 100755
--- a/tools-init.sh
+++ b/tools-init.sh
@@ -104,6 +104,7 @@ function gh_fetch_and_verify() {
 	return 1 )
 }
 
+# Put lock file in place.
 function lock_place() {
 	# Get lock, if that fails, just exit
 	if [ -f "$TMP_LOCK_FILE" ] ; then
@@ -112,13 +113,35 @@ function lock_place() {
 	fi
 
 	# Acquire lock
-	touch "$TMP_LOCK_FILE"
+	echo "$$" > "$TMP_LOCK_FILE"
+
+	# Try to detect if two instances run at the same time
+	# on the same system. Should not happen often.
+	sleep 1
+
+	if [ "$$" == `cat "$TMP_LOCK_FILE"` ] ; then
+		echo "$0: Acquired lock ($TMP_LOCK_FILE)"
+	else
+		echo "$0: Someone else got the lock before us. Bailing out"
+		exit 1
+	fi
 }
 
+# Remove lock file, but only if we acquired it.
 function lock_remove() {
-	rm -f "$TMP_LOCK_FILE"
+	if [ -f "$TMP_LOCK_FILE" ] ; then
+		if [ "$$" == `cat "$TMP_LOCK_FILE"` ] ; then
+			echo "$0: Removed lock"
+			rm -f "$TMP_LOCK_FILE"
+		else
+			echo "$0. Someone else got the lock file. Not removing lock file."
+		fi
+	fi
 }
 
+# When exiting, ensure we remove lock file.
+trap lock_remove EXIT
+
 lock_place
 
 #