[PATCH v7 09/38] lock_file(): always initialize and register lock_file object
- From
Michael Haggerty <mhagger@alum.mit.edu>
- Date
- Oct 1, 2014, 10:28 UTC
- Message-ID
- <1412159322-2622-10-git-send-email-mhagger@alum.mit.edu>
- In-Reply-To
- <1412159322-2622-1-git-send-email-mhagger@alum.mit.edu>
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@alum.mit.edu> --- 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