Hi Folks,

Sorry to get your attention.  :-)

There's a very strange problem with Mongrel where if Threads are created
because of the Mutex around Rails dispatching, then lots of ram gets
created that never seems to go away.

I boiled the problem down to this:

http://pastie.caboo.se/10194

It's a graph of the "leak" and the base code that causes it (nothing
Mongrel in it at all).  This code kind of simulates how Mongrel is
managing threads and locking Rails.

What this code does is create threads until there's 1000 in a
ThreadGroup waiting on a Mutex.  Inside the guard 30000 integers are put
inside an Array.  Don't let this distract you since it can be strings,
or even nothing and you'll see the same thing.  It's just to simulate
Rails creating all the stuff it creates, and to demonstrate that while
these objects should go away, they do not.

Then it waits in 10 second increments for these threads to go away,
calling GC.start each time.

And what happens is the graph you see (samples of mem usage of the ruby
process 1/second after 3 cycles of create/destroy threads).  Rather than
the memory for the threads and the array of integers going away, it
sticks around.  It'll dip a little bit, but not much, just tops out
there and doesn't die.  Even though all the threads are clearly gone and
none of their contents should be around.

In contrast, if you remove the Mutex then the ram behaves as you'd
expect, with it going up and then going away.

I'm hoping people way smarter with Ruby than myself can tell me why this
happens, what is wrong with this code, and how to fix it.

Thanks.

-- 
Zed A. Shaw
http://www.zedshaw.com/
http://mongrel.rubyforge.org/
http://www.lingr.com/room/3yXhqKbfPy8 -- Come get help.