Hi, Mark I'm interesting in your work. First, I'd like to know, how to do a "condition variable wait with timeout" with your exist work, Second, do you think it's possible to make ABCL supporting some atomic operations, something like ATOMIC-INCF or ATOMIC-PUSH, this can be very useful to implement some lockless algorithms. Regards, Chun Tian (binghe) 在 2011-3-18，15:50， Mark Evenson 写道：
On 3/2/11 8:50 PM, Martin Simmons wrote:
I think that the implementation of condition-wait has some major problems:
Thanks very much for the comments.
I have an [updated patch][1] that attempts to address these issues for further review for inclusion in BORDEAUX-THREADS.
[1]: http://detroit.slack.net/~evenson/abcl/bordeaux-threads-abcl-20110318a.diff
1) If no other threads are trying to claim the lock, then condition-wait will return immediately rather than waiting.
I couldn't reproduce this behavior. In ABCL, the THREADS:OBJECT-WAIT implementation is mainly a simple wrapping of the underlying [java.lang.Object.wait()][2] which clearly should wait.
[2]: http://download.oracle.com/javase/6/docs/api/java/lang/Object.html#wait%28%2...
2) If two threads are waiting in condition-wait and two other threads call condition-notify, then it is possible that only one thread will return from condition-wait because the call to acquire-lock in one of them might return nil causing it to wait again.
The DO looping construct has been replaced with a simpler subsequent BT:ACQUIRE-LOCK that should solve this bug.
3) If condition-notify is called by one thread when a waiting thread is just about to enter the threads:synchronized-on form (but before it gets synchronized), then the notify will be lost. This happens because the underlying threading primitives have no "memory" of calls to notify when nothing it waiting (which is also the expected semantics for POSIX condition variables BTW).
THREADS:SYNCHRONIZED-ON is now the first form executed by BT:CONDITION-WAIT so the window here is considerably narrowed.
Also, I think condition-notify should be using threads:object-notify rather than threads:object-notify-all.
We now use THREADS:OBJECT-NOTIFY.
-- "A screaming comes across the sky. It has happened before, but there is nothing to compare to it now."
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