Conduits [1] can help solve this problem, and recently I added a package
[2] onto Hackage to get exactly the type of concurrency that you're looking
for.
[1] http://hackage.haskell.org/package/conduit-0.2.1
[2] http://hackage.haskell.org/package/stm-conduit
On Mon, Feb 13, 2012 at 10:12 AM, Roel van Dijk
Hello,
I have a program which I believe can benefit from concurrency. But I am wondering if the mechanisms I need already exist somewhere on Hackage.
Here is a sketch of my program, in literate Haskell:
module Problem where import Control.Monad ( forM_ )
The producer produces values. It blocks until there are now more values to produce. Each value is given to a callback function.
type Producer a = (a -> IO ()) -> IO ()
The converter does some work with a value. This work is purely CPU and it is the bottleneck of the program. The amount of work it has to do is variable.
type Converter a b = a -> b
The consumer does something with the value calculated by the converter. It is very important that the consumer consumes the values in the same order as they are produced.
type Consumer b = b -> IO ()
Dummy producer, converter and consumer:
producer :: Producer Int producer callback = forM_ [1..10] callback
converter :: Converter Int Int converter = (*10)
consumer :: Consumer Int consumer = print
A simple driver. Does not exploit concurrency.
simpleDriver :: Producer a -> Converter a b -> Consumer b -> IO () simpleDriver producer converter consumer = producer (consumer . converter)
current_situation :: IO () current_situation = simpleDriver producer converter consumer
Ideally I would like a driver that spawns a worker thread for each core in my system. But the trick is in ensuring that the consumer is offered results in the same order as they are generated by the producer.
I can envision that some kind of storage is necessary to keep track of results which can not yet be offered to the consumer because it is still waiting for an earlier result.
Is there any package on Haskell that can help me with this problem? Or do I have to implement it using lower level concurrency primitives?
Regards, Roel
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