| /* |
| * Copyright (c) 2005, Junio C Hamano |
| */ |
| |
| #include "cache.h" |
| #include "lockfile.h" |
| |
| /* |
| * path = absolute or relative path name |
| * |
| * Remove the last path name element from path (leaving the preceding |
| * "/", if any). If path is empty or the root directory ("/"), set |
| * path to the empty string. |
| */ |
| static void trim_last_path_component(struct strbuf *path) |
| { |
| int i = path->len; |
| |
| /* back up past trailing slashes, if any */ |
| while (i && path->buf[i - 1] == '/') |
| i--; |
| |
| /* |
| * then go backwards until a slash, or the beginning of the |
| * string |
| */ |
| while (i && path->buf[i - 1] != '/') |
| i--; |
| |
| strbuf_setlen(path, i); |
| } |
| |
| |
| /* We allow "recursive" symbolic links. Only within reason, though */ |
| #define MAXDEPTH 5 |
| |
| /* |
| * path contains a path that might be a symlink. |
| * |
| * If path is a symlink, attempt to overwrite it with a path to the |
| * real file or directory (which may or may not exist), following a |
| * chain of symlinks if necessary. Otherwise, leave path unmodified. |
| * |
| * This is a best-effort routine. If an error occurs, path will |
| * either be left unmodified or will name a different symlink in a |
| * symlink chain that started with the original path. |
| */ |
| static void resolve_symlink(struct strbuf *path) |
| { |
| int depth = MAXDEPTH; |
| static struct strbuf link = STRBUF_INIT; |
| |
| while (depth--) { |
| if (strbuf_readlink(&link, path->buf, path->len) < 0) |
| break; |
| |
| if (is_absolute_path(link.buf)) |
| /* absolute path simply replaces p */ |
| strbuf_reset(path); |
| else |
| /* |
| * link is a relative path, so replace the |
| * last element of p with it. |
| */ |
| trim_last_path_component(path); |
| |
| strbuf_addbuf(path, &link); |
| } |
| strbuf_reset(&link); |
| } |
| |
| /* Make sure errno contains a meaningful value on error */ |
| static int lock_file(struct lock_file *lk, const char *path, int flags) |
| { |
| struct strbuf filename = STRBUF_INIT; |
| |
| strbuf_addstr(&filename, path); |
| if (!(flags & LOCK_NO_DEREF)) |
| resolve_symlink(&filename); |
| |
| strbuf_addstr(&filename, LOCK_SUFFIX); |
| lk->tempfile = create_tempfile(filename.buf); |
| strbuf_release(&filename); |
| return lk->tempfile ? lk->tempfile->fd : -1; |
| } |
| |
| /* |
| * 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) { |
| strbuf_addf(buf, _("Unable to create '%s.lock': %s.\n\n" |
| "Another git process seems to be running in this repository, e.g.\n" |
| "an editor opened by 'git commit'. Please make sure all processes\n" |
| "are terminated then try again. If it still fails, a git process\n" |
| "may have crashed in this repository earlier:\n" |
| "remove the file manually to continue."), |
| absolute_path(path), strerror(err)); |
| } else |
| strbuf_addf(buf, _("Unable to create '%s.lock': %s"), |
| absolute_path(path), strerror(err)); |
| } |
| |
| NORETURN void unable_to_lock_die(const char *path, int err) |
| { |
| struct strbuf buf = STRBUF_INIT; |
| |
| unable_to_lock_message(path, err, &buf); |
| die("%s", buf.buf); |
| } |
| |
| /* This should return a meaningful errno on failure */ |
| int hold_lock_file_for_update_timeout(struct lock_file *lk, const char *path, |
| int flags, long timeout_ms) |
| { |
| int fd = lock_file_timeout(lk, path, flags, timeout_ms); |
| if (fd < 0) { |
| if (flags & LOCK_DIE_ON_ERROR) |
| unable_to_lock_die(path, errno); |
| if (flags & LOCK_REPORT_ON_ERROR) { |
| struct strbuf buf = STRBUF_INIT; |
| unable_to_lock_message(path, errno, &buf); |
| error("%s", buf.buf); |
| strbuf_release(&buf); |
| } |
| } |
| return fd; |
| } |
| |
| char *get_locked_file_path(struct lock_file *lk) |
| { |
| struct strbuf ret = STRBUF_INIT; |
| |
| 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(struct lock_file *lk) |
| { |
| char *result_path = get_locked_file_path(lk); |
| |
| if (commit_lock_file_to(lk, result_path)) { |
| int save_errno = errno; |
| free(result_path); |
| errno = save_errno; |
| return -1; |
| } |
| free(result_path); |
| return 0; |
| } |