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Minimize the potential for deadlocks between an exiting thread and it's

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joiner by making sure all locks and unlocks occur in the same order. For
the record the lock order is: DEAD_LIST, THREAD_LIST, exiting thread, joiner
thread.

Approved by: re/rwatson
This commit is contained in:
mtm 2003-05-27 21:48:42 +00:00
parent 3f6c2641b4
commit f36826da25
1 changed files with 18 additions and 2 deletions
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20
lib/libthr/thread/thr_exit.c
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@ -94,7 +94,7 @@ _thread_exit_cleanup(void)
void
_pthread_exit(void *status)
{
pthread_t pthread;
pthread_t pthread, joiner;
int exitNow = 0;
/* Check if this thread is already in the process of exiting: */
@ -122,10 +122,27 @@ _pthread_exit(void *status)
_thread_cleanupspecific();
}
retry:
/*
* Proper lock order, to minimize deadlocks, between joining
* and exiting threads is: DEAD_LIST, THREAD_LIST, exiting, joiner.
* In order to do this *and* protect from races, we must resort
* this test-and-retry loop.
*/
joiner = curthread->joiner;
/* Lock the dead list first to maintain correct lock order */
DEAD_LIST_LOCK;
THREAD_LIST_LOCK;
_thread_critical_enter(curthread);
if (joiner != curthread->joiner) {
_thread_critical_exit(curthread);
THREAD_LIST_UNLOCK;
DEAD_LIST_UNLOCK;
goto retry;
}
/* Check if there is a thread joining this one: */
if (curthread->joiner != NULL) {
pthread = curthread->joiner;
@ -151,7 +168,6 @@ _pthread_exit(void *status)
* Add this thread to the list of dead threads, and
* also remove it from the active threads list.
*/
THREAD_LIST_LOCK;
TAILQ_INSERT_HEAD(&_dead_list, curthread, dle);
TAILQ_REMOVE(&_thread_list, curthread, tle);
PTHREAD_SET_STATE(curthread, PS_DEAD);