site_archiver@lists.apple.com Delivered-To: darwin-dev@lists.apple.com Thread-index: Acne/e/vbH8T/KPBT8iNEM7nW/ztawABn+KA Thread-topic: Darwin-dev Digest, Vol 6, Issue 119 On Wed, 27 May 2009 13:57:50 -0400, Gwynne Raskind wrote: <<SNIP>>

From the pthread_rwlock_rdlock(3) manpage:

A thread may hold multiple concurrent read locks. If so, pthread_rwlock_unlock() must be called once for each lock obtained.

And further:

[EDEADLK] The current thread already owns rwlock for writing.

My interpretation of this is that you can hold as many read locks as you like, recursively, and that EDEADLK will only show up when you try to take a write lock when you already have a read lock.

The manpage names itself as being BSD, not Darwin, so I would imagine (but not know!) that this is a characteristic of at least one of the flavors of BSD that Darwin derives from.

Finally, having a look at the source code for pthread_rwlock_rdlock() at: http://www.opensource.apple.com/source/Libc/Libc-498.1.7/pthre ads/pthread_rwlock.c

I see that EDEADLK will only be returned if the lock is held for writing by the current thread.

-- Gwynne, Daughter of the Code "This whole world is an asylum for the incurable."

Interesting. My interpretation was that one thread could hold as many DIFFERENT r/w locks at one time as it wanted (which really confused me, locks would be quite useless if you COULDN'T do so, but that is what I got out of "...for each lock obtained") Reading the code makes it much clearer though; thank you! I did one other stupid test; I locked for reading and then tried to lock for writing. I seem to have deadlocked without an error on that one. Unless that is considered normal behavior, once I confirm that it isn't a problem with my test code, I'll file a bug about it. Thanks, Cem Karan _______________________________________________ Do not post admin requests to the list. They will be ignored. Darwin-dev mailing list (Darwin-dev@lists.apple.com) Help/Unsubscribe/Update your Subscription: http://lists.apple.com/mailman/options/darwin-dev/site_archiver%40lists.appl... This email sent to site_archiver@lists.apple.com