@matheusbsbs / matheus-bagliano / commits / 04e57d4d32

lock_file(): always initialize and register lock_file object

The purpose of this change is to make the state diagram for lock_file objects simpler and deterministic. If locking fails, lock_file() sometimes leaves the lock_file object partly initialized, but sometimes not. It sometimes registers the object in lock_file_list, but sometimes not. This makes the state diagram for lock_file objects effectively indeterministic and hard to reason about. A future patch will also change the filename field into a strbuf, which needs more involved initialization, so it will become even more important that the state of a lock_file object is well-defined after a failed attempt to lock. The ambiguity doesn't currently have any ill effects, because lock_file objects cannot be removed from the lock_file_list anyway. But to make it easier to document and reason about the code, make this behavior consistent: *always* initialize the lock_file object and *always* register it in lock_file_list the first time it is used, regardless of whether an error occurs. While we're at it, make sure that all of the lock_file fields are initialized to values appropriate for an unlocked object; the caller is only responsible for making sure that on_list is set to zero before the first time it is used. Signed-off-by: Michael Haggerty <mhagger@alum.mit.edu> Signed-off-by: Junio C Hamano <gitster@pobox.com>

Michael Haggerty committed Oct 1, 2014 at 12:28 UTC 04e57d4d32541bc5dba553a31f09aa2ee456bdad

1 file changed +16 -9

lockfile.c

+16 -9

@@ -129,6 +129,22 @@ static int lock_file(struct lock_file *lk, const char *path, int flags)

129 */

130 static const size_t max_path_len = sizeof(lk->filename) - 5;

131

132 + if (!lock_file_list) {

133 + /* One-time initialization */

134 + sigchain_push_common(remove_lock_file_on_signal);

135 + atexit(remove_lock_file);

136 + }

137 +

138 + if (!lk->on_list) {

139 + /* Initialize *lk and add it to lock_file_list: */

140 + lk->fd = -1;

141 + lk->owner = 0;

142 + lk->filename[0] = 0;

143 + lk->next = lock_file_list;

144 + lock_file_list = lk;

145 + lk->on_list = 1;

146 + }

147 +

148 if (strlen(path) >= max_path_len) {

149 errno = ENAMETOOLONG;

150 return -1;

@@ -139,16 +155,7 @@ static int lock_file(struct lock_file *lk, const char *path, int flags)

155 strcat(lk->filename, ".lock");

156 lk->fd = open(lk->filename, O_RDWR | O_CREAT | O_EXCL, 0666);

157 if (0 <= lk->fd) {

142 - if (!lock_file_list) {

143 - sigchain_push_common(remove_lock_file_on_signal);

144 - atexit(remove_lock_file);

145 - }

158 lk->owner = getpid();

147 - if (!lk->on_list) {

148 - lk->next = lock_file_list;

149 - lock_file_list = lk;

150 - lk->on_list = 1;

151 - }

159 if (adjust_shared_perm(lk->filename)) {

160 int save_errno = errno;

161 error("cannot fix permission bits on %s",