Created
August 8, 2011 15:07
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let mapReduce (map : 'T1 -> Async<'T2>) | |
(reduce : 'T2 -> 'T2 -> Async<'T2>) | |
(input : seq<'T1>) : Async<'T2> = | |
let run (a: Async<'T>) (k: 'T -> unit) = | |
Async.StartWithContinuations(a, k, ignore, ignore) | |
Async.FromContinuations <| fun (ok, _, _) -> | |
let k = ref 0 | |
let agent = | |
new MailboxProcessor<_>(fun chan -> | |
async { | |
for i in 2 .. k.Value do | |
let! x = chan.Receive() | |
let! y = chan.Receive() | |
return run (reduce x y) chan.Post | |
let! r = chan.Receive() | |
return ok r | |
}) | |
k := | |
(0, input) | |
||> Seq.fold (fun count x -> | |
run (map x) agent.Post | |
count + 1) | |
agent.Start() | |
let mapReduce' (mapF : 'T1 -> Async<'T2>) | |
(reduceF : 'T2 -> 'T2 -> Async<'T2>) | |
(input : seq<'T1>) : Async<'T2> = | |
let input = Array.ofSeq input | |
let (<||>) first second = | |
async { let! results = Async.Parallel([|first; second|]) in return (results.[0], results.[1]) } | |
let rec mapReduce' s e = | |
async { | |
if s + 1 >= e then return! mapF input.[s] | |
else | |
let m = (s + e) / 2 | |
let! (left, right) = mapReduce' s m <||> mapReduce' m e | |
return! reduceF left right | |
} | |
mapReduce' 0 input.Length | |
let test mapReduce n = | |
let map x = async { if x = n then | |
do! Async.Sleep 10000 | |
return x } | |
let reduce x y = async { do! Async.Sleep 1000 | |
return x + y } | |
mapReduce map reduce [| 0 .. n |] | |
|> Async.RunSynchronously | |
#time | |
test mapReduce 100 | |
test mapReduce' 100 |
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Discussion: http://stackoverflow.com/questions/6969197/f-async-stack-overflow