1 files changed, 207 insertions, 0 deletions
diff --git a/lockfile.c b/lockfile.c
new file mode 100644
index 0000000..9268cdf
--- /dev/null
+++ b/lockfile.c
@@ -0,0 +1,207 @@
+/*
+ * 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)
+{
+	int fd;
+	struct strbuf filename = STRBUF_INIT;
+
+	strbuf_addstr(&filename, path);
+	if (!(flags & LOCK_NO_DEREF))
+		resolve_symlink(&filename);
+
+	strbuf_addstr(&filename, LOCK_SUFFIX);
+	fd = create_tempfile(&lk->tempfile, filename.buf);
+	strbuf_release(&filename);
+	return fd;
+}
+
+/*
+ * 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 && (flags & LOCK_DIE_ON_ERROR))
+		unable_to_lock_die(path, errno);
+	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;
+}