The use of O_EXCL does help, better fail then use a semaphore not owned by
the caller. O_EXCL guarantees the open will fail if the semaphore named name
already exists. If it fails with EEXIST, a new semaphore name is tried.
---
srclib/apr/locks/unix/proc_mutex.c | 23 +++++++++++------------
1 file changed, 11 insertions(+), 12 deletions(-)
Index: 2.2.x/srclib/apr/locks/unix/proc_mutex.c
===================================================================
--- 2.2.x.orig/srclib/apr/locks/unix/proc_mutex.c 2007-04-27
11:09:48.000000000 -0300
+++ 2.2.x/srclib/apr/locks/unix/proc_mutex.c 2007-04-27 11:09:52.000000000
-0300
@@ -79,23 +79,22 @@
* implementation. Versions previous to Darwin 6.2 had the 14
* char limit, but later rev's allow up to 31 characters.
*
- * FIXME: There is a small window of opportunity where
- * instead of getting a new semaphore descriptor, we get
- * a previously obtained one. This can happen if the requests
- * are made at the "same time" and in the small span of time between
- * the sem_open and the sem_unlink. Use of O_EXCL does not
- * help here however...
- *
*/
now = apr_time_now();
sec = apr_time_sec(now);
usec = apr_time_usec(now);
apr_snprintf(semname, sizeof(semname), "/ApR.%lxZ%lx", sec, usec);
- psem = sem_open(semname, O_CREAT, 0644, 1);
- if ((psem == (sem_t *)SEM_FAILED) && (errno == ENAMETOOLONG)) {
- /* Oh well, good try */
- semname[13] = '\0';
- psem = sem_open(semname, O_CREAT, 0644, 1);
+ psem = sem_open(semname, O_CREAT | O_EXCL, 0644, 1);
+ if ((psem == (sem_t *)SEM_FAILED)) {
+ if (errno == ENAMETOOLONG) {
+ /* Oh well, good try */
+ semname[13] = '\0';
+ } else if (errno == EEXIST) {
+ apr_snprintf(semname, sizeof(semname), "/ApR.%lxZ%lx", usec, sec);
+ } else {
+ return errno;
+ }
+ psem = sem_open(semname, O_CREAT | O_EXCL, 0644, 1);
}
if (psem == (sem_t *)SEM_FAILED) {
--
