queue deadlock possibility

[Delaney, Timothy (Tim)]

Michael Bayer wrote:

> i was just going through this thread: http://mail.python.org/
> pipermail/python-list/2006-April/336948.html , where it is suggested
> that the Lock instance used by Queue.Queue should be publically
> configurable.  I have identified another situation where a Queue can
> be deadlocked, one which is also alleviated by configuring the type
> of Lock used by the Queue (or just changing it to an RLock).
> 
> The scenario arises when the Queue is operated upon within the
> __del__ method of an object; since __del__ can be called at somewhat
> unpredictable times, I have observed that it is in fact possible, in
> extremely rare circumstances, for put() to be called within a get()
> or possibly vice versa; since both methods lock on the same
> underlying mutex object which is an instance of threading.Lock, a
> deadlock occurs.
> 
> The issue can be fixed by substituting a threading.RLock for the
> threading.Lock object that Queue instantiates by default.

Please a patch on SourceForge, and send an email to python-dev to alert
people of this issue (SourceForge isn't sending notification emails).

Tim Delaney