lockfile: record the primary process.

The usual process flow is the main process opens and holds the lock to
the index, does its thing, perhaps spawning children during the course,
and then writes the resulting index out by releaseing the lock.

However, the lockfile interface uses atexit(3) to clean it up, without
regard to who actually created the lock.  This typically leads to a
confusing behaviour of lock being released too early when the child
exits, and then the parent process when it calls commit_lockfile()
finds that it cannot unlock it.

This fixes the problem by recording who created and holds the lock, and
upon atexit(3) handler, child simply ignores the lockfile the parent
created.

Signed-off-by: Junio C Hamano <junkio@cox.net>

diff --git a/cache.h b/cache.h
index 8c804cb6eea5c3152b3f7e0a2cf7b4ada274280e..faddaf650449dd694a4b94885fa8449c3f413def 100644 (file)
--- a/cache.h
+++ b/cache.h
@@ -209,6 +209,7 @@ extern int refresh_cache(unsigned int flags);
 
 struct lock_file {
        struct lock_file *next;
+       pid_t owner;
        char on_list;
        char filename[PATH_MAX];
 };

diff --git a/lockfile.c b/lockfile.c
index bed6b21daf302c76cb87bb99b613f168df9899e1..23db35aff21d7c33197726128e2f120291e6e9f0 100644 (file)
--- a/lockfile.c
+++ b/lockfile.c
@@ -8,8 +8,11 @@ static const char *alternate_index_output;
 
 static void remove_lock_file(void)
 {
+       pid_t me = getpid();
+
        while (lock_file_list) {
-               if (lock_file_list->filename[0])
+               if (lock_file_list->owner == me &&
+                   lock_file_list->filename[0])
                        unlink(lock_file_list->filename);
                lock_file_list = lock_file_list->next;
        }
@@ -28,6 +31,7 @@ static int lock_file(struct lock_file *lk, const char *path)
        sprintf(lk->filename, "%s.lock", path);
        fd = open(lk->filename, O_RDWR | O_CREAT | O_EXCL, 0666);
        if (0 <= fd) {
+               lk->owner = getpid();
                if (!lk->on_list) {
                        lk->next = lock_file_list;
                        lock_file_list = lk;