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-rw-r--r--lockfile.c299
1 files changed, 82 insertions, 217 deletions
diff --git a/lockfile.c b/lockfile.c
index 9889277751..80d056d2ed 100644
--- a/lockfile.c
+++ b/lockfile.c
@@ -1,38 +1,9 @@
/*
* Copyright (c) 2005, Junio C Hamano
*/
+
#include "cache.h"
#include "lockfile.h"
-#include "sigchain.h"
-
-static struct lock_file *volatile lock_file_list;
-
-static void remove_lock_files(int skip_fclose)
-{
- pid_t me = getpid();
-
- while (lock_file_list) {
- 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(1);
- sigchain_pop(signo);
- raise(signo);
-}
/*
* path = absolute or relative path name
@@ -101,60 +72,78 @@ static void resolve_symlink(struct strbuf *path)
/* Make sure errno contains a meaningful value on error */
static int lock_file(struct lock_file *lk, const char *path, int flags)
{
- size_t pathlen = strlen(path);
+ int fd;
+ struct strbuf filename = STRBUF_INIT;
- if (!lock_file_list) {
- /* One-time initialization */
- sigchain_push_common(remove_lock_files_on_signal);
- atexit(remove_lock_files_on_exit);
- }
+ strbuf_addstr(&filename, path);
+ if (!(flags & LOCK_NO_DEREF))
+ resolve_symlink(&filename);
- if (lk->active)
- die("BUG: cannot lock_file(\"%s\") using active struct lock_file",
- path);
- 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);
- lk->next = lock_file_list;
- lock_file_list = lk;
- lk->on_list = 1;
- } else if (lk->filename.len) {
- /* This shouldn't happen, but better safe than sorry. */
- die("BUG: lock_file(\"%s\") called with improperly-reset lock_file object",
- path);
- }
+ strbuf_addstr(&filename, LOCK_SUFFIX);
+ fd = create_tempfile(&lk->tempfile, filename.buf);
+ strbuf_release(&filename);
+ return fd;
+}
- if (flags & LOCK_NO_DEREF) {
- strbuf_add_absolute_path(&lk->filename, path);
- } else {
- struct strbuf resolved_path = STRBUF_INIT;
+/*
+ * 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
- strbuf_add(&resolved_path, path, pathlen);
- resolve_symlink(&resolved_path);
- strbuf_add_absolute_path(&lk->filename, resolved_path.buf);
- strbuf_release(&resolved_path);
- }
+/*
+ * 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;
- strbuf_addstr(&lk->filename, LOCK_SUFFIX);
- lk->fd = open(lk->filename.buf, O_RDWR | O_CREAT | O_EXCL, 0666);
- if (lk->fd < 0) {
- strbuf_reset(&lk->filename);
- return -1;
+ if (timeout_ms == 0)
+ return lock_file(lk, path, flags);
+
+ if (!random_initialized) {
+ srand((unsigned int)getpid());
+ random_initialized = 1;
}
- lk->owner = getpid();
- lk->active = 1;
- if (adjust_shared_perm(lk->filename.buf)) {
- int save_errno = errno;
- error("cannot fix permission bits on %s", lk->filename.buf);
- rollback_lock_file(lk);
- errno = save_errno;
- return -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++;
}
- return lk->fd;
}
void unable_to_lock_message(const char *path, int err, struct strbuf *buf)
@@ -179,162 +168,38 @@ NORETURN void unable_to_lock_die(const char *path, int err)
}
/* 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 hold_lock_file_for_append(struct lock_file *lk, const char *path, int flags)
-{
- int fd, orig_fd;
-
- fd = lock_file(lk, path, flags);
- if (fd < 0) {
- if (flags & LOCK_DIE_ON_ERROR)
- unable_to_lock_die(path, errno);
- return fd;
- }
-
- orig_fd = open(path, O_RDONLY);
- if (orig_fd < 0) {
- if (errno != ENOENT) {
- int save_errno = errno;
-
- if (flags & LOCK_DIE_ON_ERROR)
- die("cannot open '%s' for copying", path);
- rollback_lock_file(lk);
- error("cannot open '%s' for copying", path);
- errno = save_errno;
- return -1;
- }
- } else if (copy_fd(orig_fd, fd)) {
- int save_errno = errno;
-
- if (flags & LOCK_DIE_ON_ERROR)
- exit(128);
- close(orig_fd);
- rollback_lock_file(lk);
- errno = save_errno;
- return -1;
- } else {
- close(orig_fd);
- }
- 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)
- die("BUG: get_locked_file_path() called for unlocked object");
- if (lk->filename.len <= LOCK_SUFFIX_LEN)
- die("BUG: get_locked_file_path() called for malformed lock object");
- return xmemdupz(lk->filename.buf, lk->filename.len - LOCK_SUFFIX_LEN);
-}
-
-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 (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;
-}
+ struct strbuf ret = STRBUF_INIT;
-int reopen_lock_file(struct lock_file *lk)
-{
- if (0 <= lk->fd)
- die(_("BUG: reopen a lockfile that is still open"));
- if (!lk->active)
- die(_("BUG: reopen a lockfile that has been committed"));
- lk->fd = open(lk->filename.buf, O_WRONLY);
- return lk->fd;
+ strbuf_addstr(&ret, get_tempfile_path(&lk->tempfile));
+ if (ret.len <= LOCK_SUFFIX_LEN ||
+ strcmp(ret.buf + ret.len - LOCK_SUFFIX_LEN, LOCK_SUFFIX))
+ die("BUG: get_locked_file_path() called for malformed lock object");
+ /* remove ".lock": */
+ strbuf_setlen(&ret, ret.len - LOCK_SUFFIX_LEN);
+ return strbuf_detach(&ret, NULL);
}
-int commit_lock_file_to(struct lock_file *lk, const char *path)
+int commit_lock_file(struct lock_file *lk)
{
- if (!lk->active)
- die("BUG: attempt to commit unlocked object to \"%s\"", path);
-
- if (close_lock_file(lk))
- return -1;
+ char *result_path = get_locked_file_path(lk);
- if (rename(lk->filename.buf, path)) {
+ if (commit_lock_file_to(lk, result_path)) {
int save_errno = errno;
- rollback_lock_file(lk);
+ free(result_path);
errno = save_errno;
return -1;
}
-
- lk->active = 0;
- strbuf_reset(&lk->filename);
+ free(result_path);
return 0;
}
-
-int commit_lock_file(struct lock_file *lk)
-{
- static struct strbuf result_file = STRBUF_INIT;
- int err;
-
- if (!lk->active)
- die("BUG: attempt to commit unlocked object");
-
- if (lk->filename.len <= LOCK_SUFFIX_LEN ||
- strcmp(lk->filename.buf + lk->filename.len - LOCK_SUFFIX_LEN, LOCK_SUFFIX))
- die("BUG: lockfile filename corrupt");
-
- /* remove ".lock": */
- strbuf_add(&result_file, lk->filename.buf,
- lk->filename.len - LOCK_SUFFIX_LEN);
- err = commit_lock_file_to(lk, result_file.buf);
- strbuf_reset(&result_file);
- return err;
-}
-
-void rollback_lock_file(struct lock_file *lk)
-{
- if (!lk->active)
- return;
-
- if (!close_lock_file(lk)) {
- unlink_or_warn(lk->filename.buf);
- lk->active = 0;
- strbuf_reset(&lk->filename);
- }
-}
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