lockfile: allow file locking to be retried with a timeout
Currently, there is only one attempt to lock a file. If it fails, the
whole operation fails.
But it might sometimes be advantageous to try acquiring a file lock a
few times before giving up. So add a new function,
hold_lock_file_for_update_timeout(), that allows a timeout to be
specified. Make hold_lock_file_for_update() a thin wrapper around the
new function.
If timeout_ms is positive, then retry for at least that many
milliseconds to acquire the lock. On each failed attempt, use select()
to wait for a backoff time that increases quadratically (capped at 1
second) and has a random component to prevent two processes from
getting synchronized. If timeout_ms is negative, retry indefinitely.
In a moment we will switch to using the new function when locking
packed-refs.
Signed-off-by: Michael Haggerty <mhagger@alum.mit.edu>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
diff --git a/lockfile.h b/lockfile.h
index cd2ec95..b4abc61 100644
--- a/lockfile.h
+++ b/lockfile.h
@@ -74,8 +74,20 @@
extern void unable_to_lock_message(const char *path, int err,
struct strbuf *buf);
extern NORETURN void unable_to_lock_die(const char *path, int err);
-extern int hold_lock_file_for_update(struct lock_file *, const char *path, int);
-extern int hold_lock_file_for_append(struct lock_file *, const char *path, int);
+extern int hold_lock_file_for_update_timeout(
+ struct lock_file *lk, const char *path,
+ int flags, long timeout_ms);
+
+static inline int hold_lock_file_for_update(
+ struct lock_file *lk, const char *path,
+ int flags)
+{
+ return hold_lock_file_for_update_timeout(lk, path, flags, 0);
+}
+
+extern int hold_lock_file_for_append(struct lock_file *lk, const char *path,
+ int flags);
+
extern FILE *fdopen_lock_file(struct lock_file *, const char *mode);
extern char *get_locked_file_path(struct lock_file *);
extern int commit_lock_file_to(struct lock_file *, const char *path);
