From: reynhout@...
Date: 2009-07-14T01:48:40+09:00
Subject: C ext / threading / callback issue, ruby-1.9.1p129

Hi,

I've never written a C extension for Ruby before, and I'm struggling with
some demo code which uses C and/or Ruby pthreads, and a C or Ruby callback
(address passed as an arg into the C lib).

There's a watcher thread (in C) that waits for an event (the creation of
a file), then triggers whichever callback is specified.

Triggering the Ruby callback causes MRI to crash.  The C callback works...
but when it completes, all Ruby threads appear to suspend (control is
never returned to Ruby / the threads are never rejoined?)

I'm guessing that the MRI crash is a dereferencing bug??  I haven't figured
that out obviously, but I have a feeling that the second problem (threads
never rejoin?) will show up after the crash is resolved.

I put the code up on github: http://github.com/reynhout/callme/ .  There
is a bunch more description there, too.

There are two versions, C_ext (described above), and FFI_lib which uses
ruby-ffi to achieve the same goals ... but is also failing similarly.
I worked on the FFI_lib one first, then backed down to a straight C ext
trying to simplify it and make the bugs easier to find.

I'm pretty sure that if I can get the C_ext version working, the FFI_lib
one will fall into place.  The ultimate goal is a Ruby library for Apache
ZooKeeper.  The rest of the code is going great, but many ZK functions
depend on this sort of mechanism..  

I hope the bugs are obvious to anyone who has written a C ext before.
I'd greatly appreciate any ideas or pointers (no pun intended :)..

http://github.com/reynhout/callme/

Thank you!
Andrew


-- 
reynhout@quesera.com