> On 30 Oct 2016, at 09:15, Karl <raziel.im+swift-us...@gmail.com> wrote:
>
> I had the need for a concurrent map recently. I had a part of a program which
> needed to read chunks of data and concurrently process them and assemble the
> results in an array. This isn’t necessarily as obvious as it sounds, because
> of arrays being value types. I came up with the following snippet which I’d
> like to check for correctness; it could also be helpful to others.
>
> Perhaps this is something Dispatch should provide out-of-the-box?
>
> - Karl
Ah one second, I was refactoring this and forgot to test it. Here’s the actual
code:
extension DispatchQueue {
static func concurrentMap<T>(iterations: Int, execute block: (Int) -> T) ->
[T] {
let __result = UnsafeMutableRawBufferPointer.allocate(count: iterations *
MemoryLayout<T>.stride)
defer { __result.deallocate() }
let _result = __result.baseAddress?.assumingMemoryBound(to: T.self)
let result = UnsafeMutableBufferPointer<T>(start: _result, count:
iterations)
concurrentPerform(iterations: iterations) { idx in
result[idx] = block(idx)
}
return Array(result)
}
}
extension Array {
func concurrentMap<T>(execute block: (Element)->T) -> [T] {
return DispatchQueue.concurrentMap(iterations: count) { block(self[$0]) }
}
}
Unfortunately I don’t think there’s a way to get an array to take over a +1
UnsafeMutableBufferPointer without copying.
- Karl_______________________________________________
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