From: Stephen Haberman <stephen@exigencecorp.com>
Date: Mon, 29 Sep 2008 14:55:20 +0000 (-0500)
Subject: Add a with_lock function to ensure commitnumber appends do not interweave.
X-Git-Url: http://git.droids-corp.org/?a=commitdiff_plain;h=ee0b664a1d2f1cb76abf2b487b170ae09893997a;p=git-central.git

Add a with_lock function to ensure commitnumber appends do not interweave.
---

diff --git a/server/functions b/server/functions
index b5065d3..4557d76 100644
--- a/server/functions
+++ b/server/functions
@@ -173,3 +173,37 @@ function set_describe_tags() {
 	fi
 }
 
+# Takes a lockfile path and command to execute once the lock is acquired.
+#
+# Retries every second for 5 minutes.
+#
+# with_lock "foo.lock" "echo a"             # Works
+# with_lock "foo.lock" "echo b1 ; echo b2"  # Work
+# function several() {
+# echo several1 ; echo several2
+# }
+# with_lock "foo.lock" several              # Works
+#
+function with_lock() {
+	lockfile="$1"
+	block="$2"
+	with_lock_has_lock=1
+
+	trap with_lock_unlock_if_held INT TERM EXIT
+	lockfile -1 -r 300 "$lockfile"
+	with_lock_has_lock=$?
+	if [ $with_lock_has_lock -ne 0 ] ; then
+		exit $?
+	fi
+	eval "$block"
+	rm -f "$lockfile"
+	with_lock_has_lock=1
+}
+
+function with_lock_unlock_if_held() {
+	if [[ "$with_lock_has_lock" -eq 0 ]] ; then
+		rm -f "$lockfile"
+	fi
+}
+
+
diff --git a/server/post-receive-assign-commit-numbers b/server/post-receive-assign-commit-numbers
index 46cd45a..39c3f48 100644
--- a/server/post-receive-assign-commit-numbers
+++ b/server/post-receive-assign-commit-numbers
@@ -2,13 +2,11 @@
 
 . $(dirname $0)/functions
 
-touch "$GIT_DIR/commitnumbers"
-
 while read oldrev newrev refname ; do
 	set_new_commits
 	echo "$new_commits" | git rev-list --reverse --stdin | while read commit ; do
-		if [[ $(grep "$commit" "$GIT_DIR/commitnumbers") == "" ]] ; then
-			echo "$commit" >> "$GIT_DIR/commitnumbers"
+		if [[ $(grep "$commit" "$GIT_DIR/commitnumbers" 2>/dev/null) == "" ]] ; then
+			with_lock "$GIT_DIR/commitnumbers.lock" 'echo "$commit" >> "$GIT_DIR/commitnumbers"'
 			number=$(grep --max-count=1 --line-number "$commit" "$GIT_DIR/commitnumbers" | grep -oP "^\d+(?=:)")
 			git tag "r/$number" "$commit"
 		fi