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authorMichael Haggerty <mhagger@alum.mit.edu>2014-10-01 10:28:13 (GMT)
committerJunio C Hamano <gitster@pobox.com>2014-10-01 20:43:50 (GMT)
commit04e57d4d32541bc5dba553a31f09aa2ee456bdad (patch)
tree7303402f8634a15e94c3e20461290036bdc1d4d4
parentebb8e380e98e83f32c1cc04200d3749ab4c0b90a (diff)
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lock_file(): always initialize and register lock_file object
The purpose of this change is to make the state diagram for lock_file objects simpler and deterministic. If locking fails, lock_file() sometimes leaves the lock_file object partly initialized, but sometimes not. It sometimes registers the object in lock_file_list, but sometimes not. This makes the state diagram for lock_file objects effectively indeterministic and hard to reason about. A future patch will also change the filename field into a strbuf, which needs more involved initialization, so it will become even more important that the state of a lock_file object is well-defined after a failed attempt to lock. The ambiguity doesn't currently have any ill effects, because lock_file objects cannot be removed from the lock_file_list anyway. But to make it easier to document and reason about the code, make this behavior consistent: *always* initialize the lock_file object and *always* register it in lock_file_list the first time it is used, regardless of whether an error occurs. While we're at it, make sure that all of the lock_file fields are initialized to values appropriate for an unlocked object; the caller is only responsible for making sure that on_list is set to zero before the first time it is used. Signed-off-by: Michael Haggerty <mhagger@alum.mit.edu> Signed-off-by: Junio C Hamano <gitster@pobox.com>
-rw-r--r--lockfile.c25
1 files changed, 16 insertions, 9 deletions
diff --git a/lockfile.c b/lockfile.c
index f4ce79b..81143e5 100644
--- a/lockfile.c
+++ b/lockfile.c
@@ -129,6 +129,22 @@ static int lock_file(struct lock_file *lk, const char *path, int flags)
*/
static const size_t max_path_len = sizeof(lk->filename) - 5;
+ if (!lock_file_list) {
+ /* One-time initialization */
+ sigchain_push_common(remove_lock_file_on_signal);
+ atexit(remove_lock_file);
+ }
+
+ if (!lk->on_list) {
+ /* Initialize *lk and add it to lock_file_list: */
+ lk->fd = -1;
+ lk->owner = 0;
+ lk->filename[0] = 0;
+ lk->next = lock_file_list;
+ lock_file_list = lk;
+ lk->on_list = 1;
+ }
+
if (strlen(path) >= max_path_len) {
errno = ENAMETOOLONG;
return -1;
@@ -139,16 +155,7 @@ static int lock_file(struct lock_file *lk, const char *path, int flags)
strcat(lk->filename, ".lock");
lk->fd = open(lk->filename, O_RDWR | O_CREAT | O_EXCL, 0666);
if (0 <= lk->fd) {
- if (!lock_file_list) {
- sigchain_push_common(remove_lock_file_on_signal);
- atexit(remove_lock_file);
- }
lk->owner = getpid();
- if (!lk->on_list) {
- lk->next = lock_file_list;
- lock_file_list = lk;
- lk->on_list = 1;
- }
if (adjust_shared_perm(lk->filename)) {
int save_errno = errno;
error("cannot fix permission bits on %s",