Parallel mapM on Repa arrays
In my recent work with Gibbs sampling , I've been making great use of the RVar which, in my view, provides a near ideal interface to random number generation. Sadly, I've been unable to make use of Repa due to the inability to use monadic actions in maps.
While clearly monadic maps can't be parallelized in general, it seems to me that RVar may be at least one example of a monad where effects can be safely parallelized (at least in principle; I'm not terribly familiar with the inner workings of RVar ). Namely, I want to write something like the following,
drawClass :: Sample -> RVar Class
drawClass = ...
drawClasses :: Array U DIM1 Sample -> RVar (Array U DIM1 Class)
drawClasses samples = A.mapM drawClass samples
where A.mapM would look something like,
mapM :: ParallelMonad m => (a -> m b) -> Array r sh a -> m (Array r sh b)
While clearly how this would work depends crucially on the implementation of RVar and its underlying RandomSource , in principle one would think that this would involve drawing a new random seed for each thread spawned and proceeding as usual.
Intuitively, it seems that this same idea might generalize to some other monads.
So, my question is: Could one construct a class ParallelMonad of monads for which effects can be safely parallelized (presumably inhabited by, at the least, RVar )?
What might it look like? What other monads might inhabit this class? Have others considered the possibility of how this might work in Repa?
Finally, if this notion of parallel monadic actions can't be generalized, does anyone see any nice way to make this work in the specific case of RVar (where it would be very useful)? Giving up RVar for parallelism is a very difficult trade-off.
It's probably not a good idea to do this due to inherently sequential nature of PRNGs. Instead, you might want to transition your code as follows:
main , or what have you). 下一篇: 并行mapM在Repa阵列上