Swift3.0 GCD多線程示例

///
func mainThread(){
    
    // 開一條全局隊列異步執行任務
    DispatchQueue.global().async {
        
        /*  Group的用法
         *  1. notify(依賴任務), 必須和 enter/leave在同一隊列纔會執行
         *  2. wait(任務等待)
         *  3. enter/leave 手動管理group計數,enter和leave必須配對, 可以不需要wait()
         */
        let group = DispatchGroup()
        var subTask: [DispatchQueue] = [DispatchQueue]()
        
        /* // 主線程
         DispatchQueue.main.async {  //通知ui刷新
         print("Main 刷新 UI: Begin")
         group.wait()
         Thread.sleep(forTimeInterval: 1)   //停止1秒
         print("Main 刷新 UI: End")
         }   // */
        
        //初始化8個子線程
        for i in 0...7{
            subTask.append(DispatchQueue(label: "subTask\(i)", attributes: .concurrent))
        }
        //啓動8個子線程任務
        for item in subTask{
            group.enter()   //把該任務添加到組隊列中執行, enter和leave必須配對
            item.async(group: group) {
                Thread.sleep(forTimeInterval: 1)   //停止1秒
                print("\(Date().description) subTask.label = \(item.label)")
                DispatchQueue.main.async(group: group, execute: refreshMainUI(dq: item))     // 通知主線程刷新UI
                group.leave()   //執行完之後從組隊列中移除
            }
           	group.notify(queue: item){ // 對應的子線程完成後，掃尾任務
                    print("\(item.label) finished，do something more")
                    // *** 此處可添加 對應的子線程完成後的掃尾任務
                    sleep(10)
             }
        }
    }
    
    // 通知主線程刷新UI, 有需要在主線程中執行的代碼，請添加到此
    func refreshMainUI(dq:DispatchQueue) -> DispatchWorkItem{
        let workItem = DispatchWorkItem {
            print("Refresh main UI: \(dq.label): Hello world! ")
            // *** 此處可添加 UI 刷新任務
            Thread.sleep(forTimeInterval: 5)   //停止1秒
        }
        return workItem
    }
}

Logs 如下：

 ****** Cyril Test Start ******
 2019-01-16 09:35:44 +0000 Main: Execute mainThread()
  ****** Cyril Test End ******
Waitting all test done.
2019-01-16 09:35:44 +0000 subTask.label = subTask3
2019-01-16 09:35:44 +0000 subTask.label = subTask5
2019-01-16 09:35:44 +0000 subTask.label = subTask1
2019-01-16 09:35:44 +0000 subTask.label = subTask7
2019-01-16 09:35:44 +0000 subTask.label = subTask0
2019-01-16 09:35:44 +0000 subTask.label = subTask2
2019-01-16 09:35:44 +0000 subTask.label = subTask6
2019-01-16 09:35:44 +0000 subTask.label = subTask4
All test done.
Refresh main UI: subTask2: Hello world! 
Refresh main UI: subTask3: Hello world! 
Refresh main UI: subTask1: Hello world! 
Refresh main UI: subTask0: Hello world! 
subTask0 finished，do something more
subTask2 finished，do something more
subTask3 finished，do something more
subTask1 finished，do something more
subTask4 finished，do something more
Refresh main UI: subTask4: Hello world! 
subTask5 finished，do something more
subTask6 finished，do something more
subTask7 finished，do something more
Refresh main UI: subTask5: Hello world! 
Refresh main UI: subTask7: Hello world! 
Refresh main UI: subTask6: Hello world! 

最新代碼放在gitlab上：

https://gitlab.com/cyril_j/mutils/blob/master/Swift/mainThread.swift