Re: POE+Signals : The final solution

Thanks for the patch.  Tony Cook also helped prevent this from being a  
penultimate solution by discussing some of the subtler issues.

I've applied the patch as revision 2576.  It tests clean here (OSX  
with Select, Event and IO::Poll; FreeBSD with Tk, Event, Select and  
IO::Poll).

As Philip mentioned, I plan to make a developer release next week for  
testing and a production 1.007 release if that goes well.  There's  
never too much testing, so feel free to check out a copy of the  
repository and begin your own QA procedures.

Thanks!

-- 
Rocco Caputo - [email protected]


On Jul 19, 2009, at 00:37, Philip Gwyn wrote:

> Hello POEers.
>
> This is a heads-up about problems with POE and signals.  If you use  
> a signal
> handler in POE, you are probably affected.
>
> As of 1.006, POE's event queue manipulation code isn't signal safe.   
> If a signal
> occurs while POE is removing an event from the queue (example:
> $poe_kernel->remove_alarm( $aid )), there is a chance that POE will  
> remove the
> wrong element.  POE::Queue::XS::Array probably doesn't suffer from  
> this
> problem.  Long running daemons that fork a lot of sub-processes  
> (example: pre-
> or post-forking daemons) are highly susceptable to this problem.
>
> What's more, there is a race condition between verifying the queue  
> and calling
> select() or poll().
>
> You have probably been affected by this bug, without knowing it.  If  
> you have
> seen mysterious hanging processes, POE events that are going missing  
> or other
> heisenbugs, this bug is a prime suspect.
>
> Rather then try patch around the problem, we are going to adopt a  
> "final
> solution" :
>
> Semantically, the signal handlers and the main queue are running in  
> different
> threads.  The only robust way to implement threads is share- 
> nothing.  This
> means that the signal handlers have to talk to the main queue via  
> some sort of
> conduit like a socket or pipe.
>
> The RT ticket is here :
>   https://rt.cpan.org/Ticket/Display.html?id=47966
>
> The second patch implements a signal pipe using POE::Pipe::OneWay,  
> which is
> highly portable. The previous unsafe behaviour is available if the
> POE_USE_SIGNAL_PIPE=0 env var is set.
>
> The patch has already been tested on Linux (CentOS 4) and Mac OS X  
> against all
> the POE::Loops that we could install.  If possible, it would be very  
> much
> appreciated if you could test it on your systems.  Report here on  
> list or via
> RT.
>
> A developer release is planed, to see how much smoke the CPAN testers
> release.  Then general CPAN release.
>
> Thank you,
>
> -Leolo
>
>
>