On 11/08/07, Brian Hurt
You guys might also want to take a look at the Cilk programming language, and how it managed threads. If you know C, learning Cilk is about 2 hours of work, as it's C with half a dozen extra keywords and a few new concepts. I'd love to see Cilk - C + Haskell as a programming language.
The key idea of Cilk is that it's easier to deparallelize than it is to parallelize, especially automatically. So the idea is that the program is written incredibly parallel, with huge numbers of microthreads, which are (on average) very cheap to spawn. The runtime then deparallelizes the microthreads, running multiple microthreads sequentially within a single real thread (a worker thread). Microthreads that live their entire life within a single real thread are cheap to spawn (as in "not much more expensive than a normal function call" cheap).
The problem that Cilk runs into is that it's, well, C. It doesn't deal with contention at well at all- a single microthread blocking blocks the whole worker thread- meaning, among other things, that you can have "false deadlocks", where one microthread blocks on another microthread in the same real thread, and thus acts like it's deadlocked even though it really isn't. You have greatly increased the likelyhood of raceconditions as well (mutable data and multithreading just don't mix). Plus you have all the normal fun you have with C bugs- wild pointers, buffer over runs, etc.
All of which you avoid if you replace the C aspects of Cilk with Haskell. With STM you avoid the deadlock problem entirely, and with immutable data (except for carefully coded monads) you avoid the whole race condition problem. Plus all the normal advantages Haskell has over C.
How is this any better than using "par" in Haskell? -- Sebastian Sylvan +44(0)7857-300802 UIN: 44640862