Slowdown When Using Multiple Threads to Plot

[mandli]

I have noticed that when OMP_NUM_THREADS > 1 that the last images take a much longer time to plot than with OMP_NUM_THREADS == 1. Everything else until that last set plots quickly as expected and I do not think that things are waiting around as the single thread plotting is faster overall.

[rjleveque]

I'm not sure what's going on but I don't think it's because the last png file takes longer to make, I think there's some other stuff going on after they are all created that I haven't sorted out since the logic of this module is very convoluted in the way we implemented multithreading. I did notice something strange and added a comment to #309. I will try to dig into this further...

[mandli]

That was my thought too, but have yet to track it down. Is strange that it does not seem to happen without the parallel part. Maybe there's a better way to do that in general.