golang like channels in swift

channel.swift

import XCPlayground
import Foundation
import UIKit

class Channel<T>
{
    var stream: Array<T>
    let queue: dispatch_queue_t
    let semaphore: dispatch_semaphore_t
    
    init() {
        self.stream = []
        self.semaphore = dispatch_semaphore_create(0)
        self.queue = dispatch_queue_create("channel.queue.", DISPATCH_QUEUE_CONCURRENT)
    }
    
    func write(value: T) {
        dispatch_async(self.queue) {
            self.stream.append(value)
            dispatch_semaphore_signal(self.semaphore)
        }
    }
    
    func recv() -> T {
        var result:T?
        dispatch_sync(self.queue) {
            dispatch_semaphore_wait(self.semaphore, DISPATCH_TIME_FOREVER)
            result = self.stream.removeAtIndex(0)
        }
        return result!
    }
}

let chan: Channel<String> = Channel()

dispatch_async(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_BACKGROUND, 0)) {
    for index in 0...10 {
        chan.write("ping \(index)")
        let pong = chan.recv()
        print("[A] \(index): \(pong)")
        NSThread.sleepForTimeInterval(0.1)
    }
}

dispatch_async(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_BACKGROUND, 0)) {
    for index in 0...10 {
        let ping = chan.recv()
        print("[B] \(index): \(ping)")
        chan.write("pong \(index)")
    }
}

XCPlaygroundPage.currentPage.needsIndefiniteExecution = true