1 files changed, 141 insertions, 216 deletions

diff --git a/lockfile.c b/lockfile.c
index 8fbcb6a98a..9268cdf325 100644
--- a/lockfile.c
+++ b/lockfile.c
@@ -1,61 +1,33 @@
 /*
  * Copyright (c) 2005, Junio C Hamano
  */
-#include "cache.h"
-#include "sigchain.h"
-
-static struct lock_file *lock_file_list;
-static const char *alternate_index_output;
-
-static void remove_lock_file(void)
-{
-	pid_t me = getpid();
-
-	while (lock_file_list) {
-		if (lock_file_list->owner == me &&
-		    lock_file_list->filename[0]) {
-			if (lock_file_list->fd >= 0)
-				close(lock_file_list->fd);
-			unlink_or_warn(lock_file_list->filename);
-		}
-		lock_file_list = lock_file_list->next;
-	}
-}
 
-static void remove_lock_file_on_signal(int signo)
-{
-	remove_lock_file();
-	sigchain_pop(signo);
-	raise(signo);
-}
+#include "cache.h"
+#include "lockfile.h"
 
 /*
- * p = absolute or relative path name
+ * path = absolute or relative path name
  *
- * Return a pointer into p showing the beginning of the last path name
- * element.  If p is empty or the root directory ("/"), just return p.
+ * 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 char *last_path_elm(char *p)
+static void trim_last_path_component(struct strbuf *path)
 {
-	/* r starts pointing to null at the end of the string */
-	char *r = strchr(p, '\0');
-
-	if (r == p)
-		return p; /* just return empty string */
-
-	r--; /* back up to last non-null character */
+	int i = path->len;
 
 	/* back up past trailing slashes, if any */
-	while (r > p && *r == '/')
-		r--;
+	while (i && path->buf[i - 1] == '/')
+		i--;
 
 	/*
-	 * then go backwards until I hit a slash, or the beginning of
-	 * the string
+	 * then go backwards until a slash, or the beginning of the
+	 * string
 	 */
-	while (r > p && *(r-1) != '/')
-		r--;
-	return r;
+	while (i && path->buf[i - 1] != '/')
+		i--;
+
+	strbuf_setlen(path, i);
 }
 
 
@@ -63,220 +35,173 @@ static char *last_path_elm(char *p)
 #define MAXDEPTH 5
 
 /*
- * p = path that may be a symlink
- * s = full size of p
+ * path contains a path that might be a symlink.
  *
- * If p is a symlink, attempt to overwrite p with a path to the real
- * file or directory (which may or may not exist), following a chain of
- * symlinks if necessary.  Otherwise, leave p unmodified.
+ * 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, p will either be
- * left unmodified or will name a different symlink in a symlink chain
- * that started with p's initial contents.
- *
- * Always returns p.
+ * 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 char *resolve_symlink(char *p, size_t s)
+static void resolve_symlink(struct strbuf *path)
 {
 	int depth = MAXDEPTH;
+	static struct strbuf link = STRBUF_INIT;
 
 	while (depth--) {
-		char link[PATH_MAX];
-		int link_len = readlink(p, link, sizeof(link));
-		if (link_len < 0) {
-			/* not a symlink anymore */
-			return p;
-		}
-		else if (link_len < sizeof(link))
-			/* readlink() never null-terminates */
-			link[link_len] = '\0';
-		else {
-			warning("%s: symlink too long", p);
-			return p;
-		}
-
-		if (is_absolute_path(link)) {
+		if (strbuf_readlink(&link, path->buf, path->len) < 0)
+			break;
+
+		if (is_absolute_path(link.buf))
 			/* absolute path simply replaces p */
-			if (link_len < s)
-				strcpy(p, link);
-			else {
-				warning("%s: symlink too long", p);
-				return p;
-			}
-		} else {
+			strbuf_reset(path);
+		else
 			/*
-			 * link is a relative path, so I must replace the
+			 * link is a relative path, so replace the
 			 * last element of p with it.
 			 */
-			char *r = (char *)last_path_elm(p);
-			if (r - p + link_len < s)
-				strcpy(r, link);
-			else {
-				warning("%s: symlink too long", p);
-				return p;
-			}
-		}
-	}
-	return p;
-}
-
-
-static int lock_file(struct lock_file *lk, const char *path, int flags)
-{
-	/*
-	 * subtract 5 from size to make sure there's room for adding
-	 * ".lock" for the lock file name
-	 */
-	static const size_t max_path_len = sizeof(lk->filename) - 5;
+			trim_last_path_component(path);
 
-	if (strlen(path) >= max_path_len)
-		return -1;
-	strcpy(lk->filename, path);
-	if (!(flags & LOCK_NODEREF))
-		resolve_symlink(lk->filename, max_path_len);
-	strcat(lk->filename, ".lock");
-	lk->fd = open(lk->filename, O_RDWR | O_CREAT | O_EXCL, 0666);
-	if (0 <= lk->fd) {
-		if (!lock_file_list) {
-			sigchain_push_common(remove_lock_file_on_signal);
-			atexit(remove_lock_file);
-		}
-		lk->owner = getpid();
-		if (!lk->on_list) {
-			lk->next = lock_file_list;
-			lock_file_list = lk;
-			lk->on_list = 1;
-		}
-		if (adjust_shared_perm(lk->filename))
-			return error("cannot fix permission bits on %s",
-				     lk->filename);
+		strbuf_addbuf(path, &link);
 	}
-	else
-		lk->filename[0] = 0;
-	return lk->fd;
+	strbuf_reset(&link);
 }
 
-static char *unable_to_lock_message(const char *path, int err)
+/* Make sure errno contains a meaningful value on error */
+static int lock_file(struct lock_file *lk, const char *path, int flags)
 {
-	struct strbuf buf = STRBUF_INIT;
+	int fd;
+	struct strbuf filename = STRBUF_INIT;
 
-	if (err == EEXIST) {
-		strbuf_addf(&buf, "Unable to create '%s.lock': %s.\n\n"
-		    "If no other git process is currently running, this probably means a\n"
-		    "git process crashed in this repository earlier. Make sure no other git\n"
-		    "process is running and 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));
-	return strbuf_detach(&buf, NULL);
-}
+	strbuf_addstr(&filename, path);
+	if (!(flags & LOCK_NO_DEREF))
+		resolve_symlink(&filename);
 
-int unable_to_lock_error(const char *path, int err)
-{
-	char *msg = unable_to_lock_message(path, err);
-	error("%s", msg);
-	free(msg);
-	return -1;
+	strbuf_addstr(&filename, LOCK_SUFFIX);
+	fd = create_tempfile(&lk->tempfile, filename.buf);
+	strbuf_release(&filename);
+	return fd;
 }
 
-NORETURN void unable_to_lock_index_die(const char *path, int err)
-{
-	die("%s", unable_to_lock_message(path, err));
-}
+/*
+ * 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
 
-int hold_lock_file_for_update(struct lock_file *lk, const char *path, int flags)
+/*
+ * 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 fd = lock_file(lk, path, flags);
-	if (fd < 0 && (flags & LOCK_DIE_ON_ERROR))
-		unable_to_lock_index_die(path, errno);
-	return fd;
-}
+	int n = 1;
+	int multiplier = 1;
+	long remaining_ms = 0;
+	static int random_initialized = 0;
 
-int hold_lock_file_for_append(struct lock_file *lk, const char *path, int flags)
-{
-	int fd, orig_fd;
+	if (timeout_ms == 0)
+		return lock_file(lk, path, flags);
 
-	fd = lock_file(lk, path, flags);
-	if (fd < 0) {
-		if (flags & LOCK_DIE_ON_ERROR)
-			unable_to_lock_index_die(path, errno);
-		return fd;
+	if (!random_initialized) {
+		srand((unsigned int)getpid());
+		random_initialized = 1;
 	}
 
-	orig_fd = open(path, O_RDONLY);
-	if (orig_fd < 0) {
-		if (errno != ENOENT) {
-			if (flags & LOCK_DIE_ON_ERROR)
-				die("cannot open '%s' for copying", path);
-			close(fd);
-			return error("cannot open '%s' for copying", path);
-		}
-	} else if (copy_fd(orig_fd, fd)) {
-		if (flags & LOCK_DIE_ON_ERROR)
-			exit(128);
-		close(fd);
-		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 fd;
 }
 
-int close_lock_file(struct lock_file *lk)
+void unable_to_lock_message(const char *path, int err, struct strbuf *buf)
 {
-	int fd = lk->fd;
-	lk->fd = -1;
-	return close(fd);
+	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));
 }
 
-int commit_lock_file(struct lock_file *lk)
+NORETURN void unable_to_lock_die(const char *path, int err)
 {
-	char result_file[PATH_MAX];
-	size_t i;
-	if (lk->fd >= 0 && close_lock_file(lk))
-		return -1;
-	strcpy(result_file, lk->filename);
-	i = strlen(result_file) - 5; /* .lock */
-	result_file[i] = 0;
-	if (rename(lk->filename, result_file))
-		return -1;
-	lk->filename[0] = 0;
-	return 0;
-}
+	struct strbuf buf = STRBUF_INIT;
 
-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);
+	unable_to_lock_message(path, err, &buf);
+	die("%s", buf.buf);
 }
 
-void set_alternate_index_output(const char *name)
+/* 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)
 {
-	alternate_index_output = name;
+	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 commit_locked_index(struct lock_file *lk)
+char *get_locked_file_path(struct lock_file *lk)
 {
-	if (alternate_index_output) {
-		if (lk->fd >= 0 && close_lock_file(lk))
-			return -1;
-		if (rename(lk->filename, alternate_index_output))
-			return -1;
-		lk->filename[0] = 0;
-		return 0;
-	}
-	else
-		return commit_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);
 }
 
-void rollback_lock_file(struct lock_file *lk)
+int commit_lock_file(struct lock_file *lk)
 {
-	if (lk->filename[0]) {
-		if (lk->fd >= 0)
-			close(lk->fd);
-		unlink_or_warn(lk->filename);
+	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;
 	}
-	lk->filename[0] = 0;
+	free(result_path);
+	return 0;
 }