On Mon, Jul 5, 2010 at 10:29 AM, Ertugrul Soeylemez
It happened once to me that I forgot that MVars don't have a queue. A database thread would take values out of the MVar as commands and execute them, but I used the same thread to put a command into the MVar (for later execution). It worked most of the time, unless another thread put a command concurrently, right after the last command was executed and before the database thread put another command ⇒ deadlock.
I fixed this by replacing the MVar by a Chan. Could STM have helped here?
Probably only if both "puts" were in the same transaction, I guess. Even with STM the solution is a channel, i.e. TChan.
And as a related question, how fast does STM perform in average? Is it suitable for high traffic applications (not network/file traffic, but MVar/Chan traffic)? Usually in a non-SMP setting I can easily pass hundreds of thousands of values per second through MVars between tens of thousands of threads.
As always, I guess you should benchmark :). There is some overhead, indeed, however for most applications I guess it should be fine. Specially because that overhead comes to save you from a lot of headaches. Cheers, -- Felipe.