"and gets locked up because the list's atomic lock is locked by B."
The lock is not held by B since the wait releases the lock (and reacquires it before returning). Do you have a logical explanation for the unlock/wait/lock approach? I've seen this pattern in kannel sources: lock/set mutex owner to -1/wait/set mutex owner to current thread/unlock list->single_operation_lock->owner = -1; Does anyone know its story? _____ From: Andreas Fink [mailto:[EMAIL PROTECTED] Sent: 16 April 2007 16:44 To: devel Devel Subject: Race condition in list_consume() We found a severe bug in gwlib. We have the following scenario: A calls debug("xxx",0,"xxxx") which does : gwlist_add_producer(writers); and continues but doesnt reach yet this line: gwlist_remove_producer(writers); at this point the list "writers" is empty but has writers->num_producers=1 B does: lock(list); /* atomic lock */ list->single_operation_lock->owner = -1; pthread_cond_wait(&list->nonempty, &list->single_operation_lock->mutex); so it waits until A is calling gwlist_remove_producer() and wait until A completes. Now A is calling this: void gwlist_remove_producer(List *list) { lock(list); gw_assert(list->num_producers > 0); --list->num_producers; pthread_cond_broadcast(&list->nonempty); unlock(list); } and gets locked up because the list's atomic lock is locked by B. C now has a new debug message and gets stopped at gwlist_produce(). In other words, every process who wants to write to debug log gets stuck. Now there is different solutions to this. Our approach would be to do in gwlist_consume() to do this: unlock(list); pthread_cond_wait(&list->nonempty, &list->single_operation_lock->mutex); lock(list); Any other ideas? maybe no atomic lock around gwlist_remove_producer() ? Andreas Fink Fink Consulting GmbH Global Networks Schweiz AG BebbiCell AG --------------------------------------------------------------- Tel: +41-61-6666330 Fax: +41-61-6666331 Mobile: +41-79-2457333 Address: Clarastrasse 3, 4058 Basel, Switzerland E-Mail: [EMAIL PROTECTED] www.finkconsulting.com www.global-networks.ch www.bebbicell.ch --------------------------------------------------------------- ICQ: 8239353 MSN: [EMAIL PROTECTED] AIM: smsrelay Skype: andreasfink Yahoo: finkconsulting SMS: +41792457333