static struct lock_file *volatile lock_file_list;
-static void remove_lock_files(void)
+static void remove_lock_files(int skip_fclose)
{
pid_t me = getpid();
while (lock_file_list) {
- if (lock_file_list->owner == me)
+ if (lock_file_list->owner == me) {
+ /* fclose() is not safe to call in a signal handler */
+ if (skip_fclose)
+ lock_file_list->fp = NULL;
rollback_lock_file(lock_file_list);
+ }
lock_file_list = lock_file_list->next;
}
}
+static void remove_lock_files_on_exit(void)
+{
+ remove_lock_files(0);
+}
+
static void remove_lock_files_on_signal(int signo)
{
- remove_lock_files();
+ remove_lock_files(1);
sigchain_pop(signo);
raise(signo);
}
if (!lock_file_list) {
/* One-time initialization */
sigchain_push_common(remove_lock_files_on_signal);
- atexit(remove_lock_files);
+ atexit(remove_lock_files_on_exit);
}
if (lk->active)
if (!lk->on_list) {
/* Initialize *lk and add it to lock_file_list: */
lk->fd = -1;
+ lk->fp = NULL;
lk->active = 0;
lk->owner = 0;
strbuf_init(&lk->filename, pathlen + LOCK_SUFFIX_LEN);
path);
}
- strbuf_add(&lk->filename, path, pathlen);
- if (!(flags & LOCK_NO_DEREF))
- resolve_symlink(&lk->filename);
+ if (flags & LOCK_NO_DEREF) {
+ strbuf_add_absolute_path(&lk->filename, path);
+ } else {
+ struct strbuf resolved_path = STRBUF_INIT;
+
+ strbuf_add(&resolved_path, path, pathlen);
+ resolve_symlink(&resolved_path);
+ strbuf_add_absolute_path(&lk->filename, resolved_path.buf);
+ strbuf_release(&resolved_path);
+ }
+
strbuf_addstr(&lk->filename, LOCK_SUFFIX);
lk->fd = open(lk->filename.buf, O_RDWR | O_CREAT | O_EXCL, 0666);
if (lk->fd < 0) {
return lk->fd;
}
+/*
+ * Constants defining the gaps between attempts to lock a file. The
+ * first backoff period is approximately INITIAL_BACKOFF_MS
+ * milliseconds. The longest backoff period is approximately
+ * (BACKOFF_MAX_MULTIPLIER * INITIAL_BACKOFF_MS) milliseconds.
+ */
+#define INITIAL_BACKOFF_MS 1L
+#define BACKOFF_MAX_MULTIPLIER 1000
+
+/*
+ * Try locking path, retrying with quadratic backoff for at least
+ * timeout_ms milliseconds. If timeout_ms is 0, try locking the file
+ * exactly once. If timeout_ms is -1, try indefinitely.
+ */
+static int lock_file_timeout(struct lock_file *lk, const char *path,
+ int flags, long timeout_ms)
+{
+ int n = 1;
+ int multiplier = 1;
+ long remaining_ms = 0;
+ static int random_initialized = 0;
+
+ if (timeout_ms == 0)
+ return lock_file(lk, path, flags);
+
+ if (!random_initialized) {
+ srand((unsigned int)getpid());
+ random_initialized = 1;
+ }
+
+ if (timeout_ms > 0)
+ remaining_ms = timeout_ms;
+
+ while (1) {
+ long backoff_ms, wait_ms;
+ int fd;
+
+ fd = lock_file(lk, path, flags);
+
+ if (fd >= 0)
+ return fd; /* success */
+ else if (errno != EEXIST)
+ return -1; /* failure other than lock held */
+ else if (timeout_ms > 0 && remaining_ms <= 0)
+ return -1; /* failure due to timeout */
+
+ backoff_ms = multiplier * INITIAL_BACKOFF_MS;
+ /* back off for between 0.75*backoff_ms and 1.25*backoff_ms */
+ wait_ms = (750 + rand() % 500) * backoff_ms / 1000;
+ sleep_millisec(wait_ms);
+ remaining_ms -= wait_ms;
+
+ /* Recursion: (n+1)^2 = n^2 + 2n + 1 */
+ multiplier += 2*n + 1;
+ if (multiplier > BACKOFF_MAX_MULTIPLIER)
+ multiplier = BACKOFF_MAX_MULTIPLIER;
+ else
+ n++;
+ }
+}
+
void unable_to_lock_message(const char *path, int err, struct strbuf *buf)
{
if (err == EEXIST) {
absolute_path(path), strerror(err));
}
-int unable_to_lock_error(const char *path, int err)
-{
- struct strbuf buf = STRBUF_INIT;
-
- unable_to_lock_message(path, err, &buf);
- error("%s", buf.buf);
- strbuf_release(&buf);
- return -1;
-}
-
NORETURN void unable_to_lock_die(const char *path, int err)
{
struct strbuf buf = STRBUF_INIT;
}
/* This should return a meaningful errno on failure */
-int hold_lock_file_for_update(struct lock_file *lk, const char *path, int flags)
+int hold_lock_file_for_update_timeout(struct lock_file *lk, const char *path,
+ int flags, long timeout_ms)
{
- int fd = lock_file(lk, path, flags);
+ int fd = lock_file_timeout(lk, path, flags, timeout_ms);
if (fd < 0 && (flags & LOCK_DIE_ON_ERROR))
unable_to_lock_die(path, errno);
return fd;
int save_errno = errno;
if (flags & LOCK_DIE_ON_ERROR)
- exit(128);
+ die("failed to prepare '%s' for appending", path);
close(orig_fd);
rollback_lock_file(lk);
errno = save_errno;
return fd;
}
+FILE *fdopen_lock_file(struct lock_file *lk, const char *mode)
+{
+ if (!lk->active)
+ die("BUG: fdopen_lock_file() called for unlocked object");
+ if (lk->fp)
+ die("BUG: fdopen_lock_file() called twice for file '%s'", lk->filename.buf);
+
+ lk->fp = fdopen(lk->fd, mode);
+ return lk->fp;
+}
+
char *get_locked_file_path(struct lock_file *lk)
{
if (!lk->active)
int close_lock_file(struct lock_file *lk)
{
int fd = lk->fd;
+ FILE *fp = lk->fp;
+ int err;
if (fd < 0)
return 0;
lk->fd = -1;
- if (close(fd)) {
+ if (fp) {
+ lk->fp = NULL;
+
+ /*
+ * Note: no short-circuiting here; we want to fclose()
+ * in any case!
+ */
+ err = ferror(fp) | fclose(fp);
+ } else {
+ err = close(fd);
+ }
+
+ if (err) {
int save_errno = errno;
rollback_lock_file(lk);
errno = save_errno;
return -1;
}
+
return 0;
}