The purpose of this patch 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 inconsistent: *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@xxxxxxxxxxxx>
---
lockfile.c | 25 ++++++++++++++++---------
1 file 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",
--
2.1.0
--
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