Swift 3.0 —GCD

常用场景：使用global queue完成操作后切换到main queue更新UI

DispatchQueue.global().async {
    //code
    DispatchQueue.main.async {
        //update ui
    }
}

使用Custom Queue

let serialQueue = DispatchQueue(label: "com.serialQueue.dispatch")
let concurrentQueue = DispatchQueue(label: "com.concurrentQueue.dispatch", qos: .background, attributes:.concurrent)

延迟调用

let delay = DispatchTime.now() + DispatchTimeInterval.seconds(3)
DispatchQueue.main.asyncAfter(deadline: delay) { 
    print("delay 3 seconds")
}

使用Group管理多个Queue,可以使用notify等到结束通知，使用wait等待group中所有操作执行完毕

let group = DispatchGroup()

let bookQueue = DispatchQueue(label: "com.group.book")
bookQueue.async(group: group) { 
    //down load books
}

let videoQueue = DispatchQueue(label: "com.group.video")
videoQueue.async(group: group) { 
    //down load videos
}
group.notify(queue: DispatchQueue.main) { 
    //download finished
}
group.wait()

DispatchWorkItem代替了原先的dispatch_block_t

let workItem = DispatchWorkItem { 
    //work item
}

DispatchQueue.global().async(execute: workItem)

GCD Timer

let myQueueTimer = DispatchQueue(label: "myQueueTimer", attributes: .concurrent)

let myTimer = DispatchSource.makeTimerSource(queue: myQueueTimer)

myTimer.scheduleRepeating(wallDeadline: DispatchWallTime.now(), interval: .seconds(1))
myTimer.setEventHandler {
    //TODO
}
myTimer.resume()

总结：

Swift 3.0中，GCD更加面向对象化，增强了可读性和易用性