[armedbear-devel] [Bordeaux-threads-devel] [Updated4] Patch for ABCL against BORDEAUX-THREADS HEAD

[Chun Tian (binghe)]

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%29
> 
>> 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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