Merge branch 'dt/commit-preserve-base-index-upon-opportunistic-cache-tree-update...
[git/debian.git] / lockfile.c
blob993bb8274833651159cec6f0571b5b555ea073ca
1 /*
2 * Copyright (c) 2005, Junio C Hamano
3 */
4 #include "cache.h"
5 #include "lockfile.h"
6 #include "sigchain.h"
8 static struct lock_file *volatile lock_file_list;
10 static void remove_lock_files(int skip_fclose)
12 pid_t me = getpid();
14 while (lock_file_list) {
15 if (lock_file_list->owner == me) {
16 /* fclose() is not safe to call in a signal handler */
17 if (skip_fclose)
18 lock_file_list->fp = NULL;
19 rollback_lock_file(lock_file_list);
21 lock_file_list = lock_file_list->next;
25 static void remove_lock_files_on_exit(void)
27 remove_lock_files(0);
30 static void remove_lock_files_on_signal(int signo)
32 remove_lock_files(1);
33 sigchain_pop(signo);
34 raise(signo);
38 * path = absolute or relative path name
40 * Remove the last path name element from path (leaving the preceding
41 * "/", if any). If path is empty or the root directory ("/"), set
42 * path to the empty string.
44 static void trim_last_path_component(struct strbuf *path)
46 int i = path->len;
48 /* back up past trailing slashes, if any */
49 while (i && path->buf[i - 1] == '/')
50 i--;
53 * then go backwards until a slash, or the beginning of the
54 * string
56 while (i && path->buf[i - 1] != '/')
57 i--;
59 strbuf_setlen(path, i);
63 /* We allow "recursive" symbolic links. Only within reason, though */
64 #define MAXDEPTH 5
67 * path contains a path that might be a symlink.
69 * If path is a symlink, attempt to overwrite it with a path to the
70 * real file or directory (which may or may not exist), following a
71 * chain of symlinks if necessary. Otherwise, leave path unmodified.
73 * This is a best-effort routine. If an error occurs, path will
74 * either be left unmodified or will name a different symlink in a
75 * symlink chain that started with the original path.
77 static void resolve_symlink(struct strbuf *path)
79 int depth = MAXDEPTH;
80 static struct strbuf link = STRBUF_INIT;
82 while (depth--) {
83 if (strbuf_readlink(&link, path->buf, path->len) < 0)
84 break;
86 if (is_absolute_path(link.buf))
87 /* absolute path simply replaces p */
88 strbuf_reset(path);
89 else
91 * link is a relative path, so replace the
92 * last element of p with it.
94 trim_last_path_component(path);
96 strbuf_addbuf(path, &link);
98 strbuf_reset(&link);
101 /* Make sure errno contains a meaningful value on error */
102 static int lock_file(struct lock_file *lk, const char *path, int flags)
104 size_t pathlen = strlen(path);
106 if (!lock_file_list) {
107 /* One-time initialization */
108 sigchain_push_common(remove_lock_files_on_signal);
109 atexit(remove_lock_files_on_exit);
112 if (lk->active)
113 die("BUG: cannot lock_file(\"%s\") using active struct lock_file",
114 path);
115 if (!lk->on_list) {
116 /* Initialize *lk and add it to lock_file_list: */
117 lk->fd = -1;
118 lk->fp = NULL;
119 lk->active = 0;
120 lk->owner = 0;
121 strbuf_init(&lk->filename, pathlen + LOCK_SUFFIX_LEN);
122 lk->next = lock_file_list;
123 lock_file_list = lk;
124 lk->on_list = 1;
125 } else if (lk->filename.len) {
126 /* This shouldn't happen, but better safe than sorry. */
127 die("BUG: lock_file(\"%s\") called with improperly-reset lock_file object",
128 path);
131 if (flags & LOCK_NO_DEREF) {
132 strbuf_add_absolute_path(&lk->filename, path);
133 } else {
134 struct strbuf resolved_path = STRBUF_INIT;
136 strbuf_add(&resolved_path, path, pathlen);
137 resolve_symlink(&resolved_path);
138 strbuf_add_absolute_path(&lk->filename, resolved_path.buf);
139 strbuf_release(&resolved_path);
142 strbuf_addstr(&lk->filename, LOCK_SUFFIX);
143 lk->fd = open(lk->filename.buf, O_RDWR | O_CREAT | O_EXCL, 0666);
144 if (lk->fd < 0) {
145 strbuf_reset(&lk->filename);
146 return -1;
148 lk->owner = getpid();
149 lk->active = 1;
150 if (adjust_shared_perm(lk->filename.buf)) {
151 int save_errno = errno;
152 error("cannot fix permission bits on %s", lk->filename.buf);
153 rollback_lock_file(lk);
154 errno = save_errno;
155 return -1;
157 return lk->fd;
161 * Constants defining the gaps between attempts to lock a file. The
162 * first backoff period is approximately INITIAL_BACKOFF_MS
163 * milliseconds. The longest backoff period is approximately
164 * (BACKOFF_MAX_MULTIPLIER * INITIAL_BACKOFF_MS) milliseconds.
166 #define INITIAL_BACKOFF_MS 1L
167 #define BACKOFF_MAX_MULTIPLIER 1000
170 * Try locking path, retrying with quadratic backoff for at least
171 * timeout_ms milliseconds. If timeout_ms is 0, try locking the file
172 * exactly once. If timeout_ms is -1, try indefinitely.
174 static int lock_file_timeout(struct lock_file *lk, const char *path,
175 int flags, long timeout_ms)
177 int n = 1;
178 int multiplier = 1;
179 long remaining_ms = 0;
180 static int random_initialized = 0;
182 if (timeout_ms == 0)
183 return lock_file(lk, path, flags);
185 if (!random_initialized) {
186 srand((unsigned int)getpid());
187 random_initialized = 1;
190 if (timeout_ms > 0)
191 remaining_ms = timeout_ms;
193 while (1) {
194 long backoff_ms, wait_ms;
195 int fd;
197 fd = lock_file(lk, path, flags);
199 if (fd >= 0)
200 return fd; /* success */
201 else if (errno != EEXIST)
202 return -1; /* failure other than lock held */
203 else if (timeout_ms > 0 && remaining_ms <= 0)
204 return -1; /* failure due to timeout */
206 backoff_ms = multiplier * INITIAL_BACKOFF_MS;
207 /* back off for between 0.75*backoff_ms and 1.25*backoff_ms */
208 wait_ms = (750 + rand() % 500) * backoff_ms / 1000;
209 sleep_millisec(wait_ms);
210 remaining_ms -= wait_ms;
212 /* Recursion: (n+1)^2 = n^2 + 2n + 1 */
213 multiplier += 2*n + 1;
214 if (multiplier > BACKOFF_MAX_MULTIPLIER)
215 multiplier = BACKOFF_MAX_MULTIPLIER;
216 else
217 n++;
221 void unable_to_lock_message(const char *path, int err, struct strbuf *buf)
223 if (err == EEXIST) {
224 strbuf_addf(buf, "Unable to create '%s.lock': %s.\n\n"
225 "If no other git process is currently running, this probably means a\n"
226 "git process crashed in this repository earlier. Make sure no other git\n"
227 "process is running and remove the file manually to continue.",
228 absolute_path(path), strerror(err));
229 } else
230 strbuf_addf(buf, "Unable to create '%s.lock': %s",
231 absolute_path(path), strerror(err));
234 NORETURN void unable_to_lock_die(const char *path, int err)
236 struct strbuf buf = STRBUF_INIT;
238 unable_to_lock_message(path, err, &buf);
239 die("%s", buf.buf);
242 /* This should return a meaningful errno on failure */
243 int hold_lock_file_for_update_timeout(struct lock_file *lk, const char *path,
244 int flags, long timeout_ms)
246 int fd = lock_file_timeout(lk, path, flags, timeout_ms);
247 if (fd < 0 && (flags & LOCK_DIE_ON_ERROR))
248 unable_to_lock_die(path, errno);
249 return fd;
252 int hold_lock_file_for_append(struct lock_file *lk, const char *path, int flags)
254 int fd, orig_fd;
256 fd = lock_file(lk, path, flags);
257 if (fd < 0) {
258 if (flags & LOCK_DIE_ON_ERROR)
259 unable_to_lock_die(path, errno);
260 return fd;
263 orig_fd = open(path, O_RDONLY);
264 if (orig_fd < 0) {
265 if (errno != ENOENT) {
266 int save_errno = errno;
268 if (flags & LOCK_DIE_ON_ERROR)
269 die("cannot open '%s' for copying", path);
270 rollback_lock_file(lk);
271 error("cannot open '%s' for copying", path);
272 errno = save_errno;
273 return -1;
275 } else if (copy_fd(orig_fd, fd)) {
276 int save_errno = errno;
278 if (flags & LOCK_DIE_ON_ERROR)
279 die("failed to prepare '%s' for appending", path);
280 close(orig_fd);
281 rollback_lock_file(lk);
282 errno = save_errno;
283 return -1;
284 } else {
285 close(orig_fd);
287 return fd;
290 FILE *fdopen_lock_file(struct lock_file *lk, const char *mode)
292 if (!lk->active)
293 die("BUG: fdopen_lock_file() called for unlocked object");
294 if (lk->fp)
295 die("BUG: fdopen_lock_file() called twice for file '%s'", lk->filename.buf);
297 lk->fp = fdopen(lk->fd, mode);
298 return lk->fp;
301 char *get_locked_file_path(struct lock_file *lk)
303 if (!lk->active)
304 die("BUG: get_locked_file_path() called for unlocked object");
305 if (lk->filename.len <= LOCK_SUFFIX_LEN)
306 die("BUG: get_locked_file_path() called for malformed lock object");
307 return xmemdupz(lk->filename.buf, lk->filename.len - LOCK_SUFFIX_LEN);
310 int close_lock_file(struct lock_file *lk)
312 int fd = lk->fd;
313 FILE *fp = lk->fp;
314 int err;
316 if (fd < 0)
317 return 0;
319 lk->fd = -1;
320 if (fp) {
321 lk->fp = NULL;
324 * Note: no short-circuiting here; we want to fclose()
325 * in any case!
327 err = ferror(fp) | fclose(fp);
328 } else {
329 err = close(fd);
332 if (err) {
333 int save_errno = errno;
334 rollback_lock_file(lk);
335 errno = save_errno;
336 return -1;
339 return 0;
342 int reopen_lock_file(struct lock_file *lk)
344 if (0 <= lk->fd)
345 die(_("BUG: reopen a lockfile that is still open"));
346 if (!lk->active)
347 die(_("BUG: reopen a lockfile that has been committed"));
348 lk->fd = open(lk->filename.buf, O_WRONLY);
349 return lk->fd;
352 int commit_lock_file_to(struct lock_file *lk, const char *path)
354 if (!lk->active)
355 die("BUG: attempt to commit unlocked object to \"%s\"", path);
357 if (close_lock_file(lk))
358 return -1;
360 if (rename(lk->filename.buf, path)) {
361 int save_errno = errno;
362 rollback_lock_file(lk);
363 errno = save_errno;
364 return -1;
367 lk->active = 0;
368 strbuf_reset(&lk->filename);
369 return 0;
372 int commit_lock_file(struct lock_file *lk)
374 static struct strbuf result_file = STRBUF_INIT;
375 int err;
377 if (!lk->active)
378 die("BUG: attempt to commit unlocked object");
380 if (lk->filename.len <= LOCK_SUFFIX_LEN ||
381 strcmp(lk->filename.buf + lk->filename.len - LOCK_SUFFIX_LEN, LOCK_SUFFIX))
382 die("BUG: lockfile filename corrupt");
384 /* remove ".lock": */
385 strbuf_add(&result_file, lk->filename.buf,
386 lk->filename.len - LOCK_SUFFIX_LEN);
387 err = commit_lock_file_to(lk, result_file.buf);
388 strbuf_reset(&result_file);
389 return err;
392 void rollback_lock_file(struct lock_file *lk)
394 if (!lk->active)
395 return;
397 if (!close_lock_file(lk)) {
398 unlink_or_warn(lk->filename.buf);
399 lk->active = 0;
400 strbuf_reset(&lk->filename);