refs file backend: move raceproof_create_file() here
Move the raceproof_create_file() API added to cache.h and
object-file.c in 177978f56ad (raceproof_create_file(): new function,
2017-01-06) to its only user, refs/files-backend.c.
Signed-off-by: Ævar Arnfjörð Bjarmason <avarab@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
diff --git a/refs/files-backend.c b/refs/files-backend.c
index ab666af..950f973 100644
--- a/refs/files-backend.c
+++ b/refs/files-backend.c
@@ -852,6 +852,115 @@ static struct ref_iterator *files_ref_iterator_begin(
return ref_iterator;
}
+/*
+ * Callback function for raceproof_create_file(). This function is
+ * expected to do something that makes dirname(path) permanent despite
+ * the fact that other processes might be cleaning up empty
+ * directories at the same time. Usually it will create a file named
+ * path, but alternatively it could create another file in that
+ * directory, or even chdir() into that directory. The function should
+ * return 0 if the action was completed successfully. On error, it
+ * should return a nonzero result and set errno.
+ * raceproof_create_file() treats two errno values specially:
+ *
+ * - ENOENT -- dirname(path) does not exist. In this case,
+ * raceproof_create_file() tries creating dirname(path)
+ * (and any parent directories, if necessary) and calls
+ * the function again.
+ *
+ * - EISDIR -- the file already exists and is a directory. In this
+ * case, raceproof_create_file() removes the directory if
+ * it is empty (and recursively any empty directories that
+ * it contains) and calls the function again.
+ *
+ * Any other errno causes raceproof_create_file() to fail with the
+ * callback's return value and errno.
+ *
+ * Obviously, this function should be OK with being called again if it
+ * fails with ENOENT or EISDIR. In other scenarios it will not be
+ * called again.
+ */
+typedef int create_file_fn(const char *path, void *cb);
+
+/*
+ * Create a file in dirname(path) by calling fn, creating leading
+ * directories if necessary. Retry a few times in case we are racing
+ * with another process that is trying to clean up the directory that
+ * contains path. See the documentation for create_file_fn for more
+ * details.
+ *
+ * Return the value and set the errno that resulted from the most
+ * recent call of fn. fn is always called at least once, and will be
+ * called more than once if it returns ENOENT or EISDIR.
+ */
+static int raceproof_create_file(const char *path, create_file_fn fn, void *cb)
+{
+ /*
+ * The number of times we will try to remove empty directories
+ * in the way of path. This is only 1 because if another
+ * process is racily creating directories that conflict with
+ * us, we don't want to fight against them.
+ */
+ int remove_directories_remaining = 1;
+
+ /*
+ * The number of times that we will try to create the
+ * directories containing path. We are willing to attempt this
+ * more than once, because another process could be trying to
+ * clean up empty directories at the same time as we are
+ * trying to create them.
+ */
+ int create_directories_remaining = 3;
+
+ /* A scratch copy of path, filled lazily if we need it: */
+ struct strbuf path_copy = STRBUF_INIT;
+
+ int ret, save_errno;
+
+ /* Sanity check: */
+ assert(*path);
+
+retry_fn:
+ ret = fn(path, cb);
+ save_errno = errno;
+ if (!ret)
+ goto out;
+
+ if (errno == EISDIR && remove_directories_remaining-- > 0) {
+ /*
+ * A directory is in the way. Maybe it is empty; try
+ * to remove it:
+ */
+ if (!path_copy.len)
+ strbuf_addstr(&path_copy, path);
+
+ if (!remove_dir_recursively(&path_copy, REMOVE_DIR_EMPTY_ONLY))
+ goto retry_fn;
+ } else if (errno == ENOENT && create_directories_remaining-- > 0) {
+ /*
+ * Maybe the containing directory didn't exist, or
+ * maybe it was just deleted by a process that is
+ * racing with us to clean up empty directories. Try
+ * to create it:
+ */
+ enum scld_error scld_result;
+
+ if (!path_copy.len)
+ strbuf_addstr(&path_copy, path);
+
+ do {
+ scld_result = safe_create_leading_directories(path_copy.buf);
+ if (scld_result == SCLD_OK)
+ goto retry_fn;
+ } while (scld_result == SCLD_VANISHED && create_directories_remaining-- > 0);
+ }
+
+out:
+ strbuf_release(&path_copy);
+ errno = save_errno;
+ return ret;
+}
+
static int remove_empty_directories(struct strbuf *path)
{
/*
