Re: [Boost-users] [signals] thread_safe_signals feature-complete

From: Timmo Stange (ts_at_[hidden])
Date: 2007-02-18 13:08:55

Frank Mori Hess wrote:

> On Sunday 18 February 2007 12:08 am, Gottlob Frege wrote:
>> - do you hold any locks DURING the slot call?  That's typically bad,
>> since you have no idea what else is locked or what a slot might do, so
>> deadlocks abound.
> 
> Well, neither implementation will deadlock, except for lock-ordering 
> problems between external mutexes and the ones inside the signals 
> implementation.  I've got a list lock and a slot lock, and only the slot 
> lock is held while the slot is executing.  I took care that it is safe to 
> do a blocking lock on the list lock while a slot lock is already held, and 
> the slot lock itself is recursive so I don't see any deadlocks.  

Consider two slots which will mutually disconnect the other in a
situation of concurrent signal invocation. With each thread holding
the lock of either slot (because of the invocation), neither would
be able to disconnect the other - a deadlock.

My implementation can similarly deadlock when two signals are involved.

Regards

Timmo Stange