From: Elias Karakoulakis <ek@...>
Date: 2003-02-09T17:42:09+09:00
Subject: Threading problem

Hello all,

I've been occasionally stumbled upon a strange problem with Ruby's 
threads, that I cannot pinpoint its exact origin. I get occasional race 
conditions where the Ruby interpreter consumes all my memory until the 
Linux VM goes into action to kill processes (sometimes X11 too!!).

We use Ruby for our Web Application Framework all throughout the 
hierarchy (from low-level HTTP handling to higher-level scripting). The 
server uses multiple threads to service HTTP requests (one per socket). 
Sometimes, and under no particular occasion, the server enters a 100% 
CPU loop and consumes all memory until its death. We are taking all 
necessary precautions (at least we think we do) to serialize access to 
shared data and other critical sections of the code, using the Sync class.

What's interesting is that this exception pops up in our logs:

   Sync_m::Err::UnknownLocker: Thread(#<Thread:0x2040e560 run>) not locked.

Taking a look inside sync.rb, this particular error occurs if the 
blocking thread leaving a critical section doesn't hold the mutex/lock 
anymore!!! Any ideas?

We are using Ruby 1.6.8 on Linux and AIX and the error appears (although 
not in a reproducable manner) regardless of the platform used. Just for 
the records, we use gcc-3.2 on SuSE 8.0 (Linux-2.4.18) and IBM's XLC 6.0 
on AIX 5.2.

Thanks for your time, and sorry of this isn't the correct place to post 
queries like this.

Elias