On Wed, Nov 11, 2009 at 9:51 AM, Bryan O'Sullivan <bos@serpentine.com> wrote:

On Wed, Nov 11, 2009 at 7:43 AM, David Leimbach <leimy2k@gmail.com> wrote:

I recently ran into some serious space leak difficulties that would ultimately cause this program to crash some time after startup (my simulator is also written in Haskell, and runs a LOT faster than the real application ever could, this has enabled me to fast forward a bit the data growth issues and crash in minutes instead of days!)

It sounds to me like you were storing a Map in a StateT. Since the usual State and StateT monads don't force the evaluation of their payload, I'm not terribly surprised that such a leak should arise.

That's exactly what was happening. The system was being far too lazy (by choices I made but didn't fully understand).

By pulling the Map out of the state, and pushing it back into the state, as the definition of my looping, things got a lot better.

I didn't see another *easy* way to force the state to be evaluated, except by doing IO on intermediate values. seq will only evaluate strictly if it's just underneath something else that's already been evaluated :-). The runtime doesn't look for "seq"s to force evaluation on.

I figured I was better off just creating a dependency in the evaluation, near the outermost portion of the program (the loop) that would cause a strict evaluation, and so far I was right :-)

Program behaves very well now, and responds much better too.

Dave