* Copyright (c) 2005, Junio C Hamano
*/
#include "cache.h"
+#include "lockfile.h"
#include "sigchain.h"
-/*
- * File write-locks as used by Git.
- *
- * For an overview of how to use the lockfile API, please see
- *
- * Documentation/technical/api-lockfile.txt
- *
- * This module keeps track of all locked files in lock_file_list for
- * use at cleanup. This list and the lock_file objects that comprise
- * it must be kept in self-consistent states at all time, because the
- * program can be interrupted any time by a signal, in which case the
- * signal handler will walk through the list attempting to clean up
- * any open lock files.
- *
- * A lockfile is owned by the process that created it. The lock_file
- * object has an "owner" field that records its owner. This field is
- * used to prevent a forked process from closing a lockfile created by
- * its parent.
- *
- * The possible states of a lock_file object are as follows:
- *
- * - Uninitialized. In this state the object's on_list field must be
- * zero but the rest of its contents need not be initialized. As
- * soon as the object is used in any way, it is irrevocably
- * registered in the lock_file_list, and on_list is set.
- *
- * - Locked, lockfile open (after hold_lock_file_for_update(),
- * hold_lock_file_for_append(), or reopen_lock_file()). In this
- * state:
- * - the lockfile exists
- * - active is set
- * - filename holds the filename of the lockfile
- * - fd holds a file descriptor open for writing to the lockfile
- * - owner holds the PID of the process that locked the file
- *
- * - Locked, lockfile closed (after successful close_lock_file()).
- * Same as the previous state, except that the lockfile is closed
- * and fd is -1.
- *
- * - Unlocked (after commit_lock_file(), commit_lock_file_to(),
- * rollback_lock_file(), a failed attempt to lock, or a failed
- * close_lock_file()). In this state:
- * - active is unset
- * - filename is empty (usually, though there are transitory
- * states in which this condition doesn't hold). Client code should
- * *not* rely on the filename being empty in this state.
- * - fd is -1
- * - the object is left registered in the lock_file_list, and
- * on_list is set.
- */
-
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;
}
+static int sleep_microseconds(long us)
+{
+ struct timeval tv;
+ tv.tv_sec = 0;
+ tv.tv_usec = us;
+ return select(0, NULL, NULL, NULL, &tv);
+}
+
+/*
+ * 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_us = 0;
+ static int random_initialized = 0;
+
+ if (timeout_ms == 0)
+ return lock_file(lk, path, flags);
+
+ if (!random_initialized) {
+ srandom((unsigned int)getpid());
+ random_initialized = 1;
+ }
+
+ if (timeout_ms > 0) {
+ /* avoid overflow */
+ if (timeout_ms <= LONG_MAX / 1000)
+ remaining_us = timeout_ms * 1000;
+ else
+ remaining_us = LONG_MAX;
+ }
+
+ while (1) {
+ long backoff_ms, wait_us;
+ 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_us <= 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_us = (750 + random() % 500) * backoff_ms;
+ sleep_microseconds(wait_us);
+ remaining_us -= wait_us;
+
+ /* 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;
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);
- return error("cannot open '%s' for copying", path);
+ 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);
+ die("failed to prepare '%s' for appending", path);
+ 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 (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;
}
return err;
}
-int hold_locked_index(struct lock_file *lk, int die_on_error)
-{
- return hold_lock_file_for_update(lk, get_index_file(),
- die_on_error
- ? LOCK_DIE_ON_ERROR
- : 0);
-}
-
void rollback_lock_file(struct lock_file *lk)
{
if (!lk->active)