Async.swift

Async.swift

import Foundation

typealias Callback = () -> ()
typealias DoneCallback = (error: NSError?) -> ()
typealias ItemCallback = (i: Int, done: DoneCallback) -> ()

func each(range: Range<Int>, exec: ItemCallback, done: DoneCallback) {
    var pending = 0
    
    for i in range {
        pending++
        
        runAsync {
            exec(i: i) { (error) in
                if pending <= 0 { return }
                
                if error != nil {
                    pending = 0
                    done(error: error)
                    return
                }
                
                if (--pending <= 0) {
                    done(error: nil)
                }
            }
        }
    }
}

func eachSeries(range: Range<Int>, exec: ItemCallback, done: DoneCallback) {
    eachSeriesStep(range.generate(), exec, done)
}

func eachSeriesStep(var generator: RangeGenerator<Int>, exec: ItemCallback, done: DoneCallback) {
    if let i = generator.next() {
        exec(i: i) { error in
            if error != nil {
                done(error: error)
                return
            }
            
            eachSeriesStep(generator, exec, done)
        }
    } else {
        done(error: nil)
    }
}

func runAsync(block: dispatch_block_t) {
    dispatch_async(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0), block)
}