GCD swift dispatch_set_target_queue 小例

首先先看一段GCD代码：

func begainDemo(){

let  Queue1  = DispatchQueue(label:"Queue1")

let  Queue2  = DispatchQueue(label:"Queue2",attributes:DispatchQueue.Attributes.concurrent)

        Queue1.async {

print("task 1 in ----\(Thread.current)")

Thread.sleep(forTimeInterval: 3)

print("task 1 out")

        }

        Queue2.async {

print("task 2 in ----\(Thread.current)")

Thread.sleep(forTimeInterval: 3)

print("task 2 out")

        }

        Queue2.async {

print("task 3 in ----\(Thread.current)")

Thread.sleep(forTimeInterval: 3)

print("task 3 out")

        }

 }

打印结果如下：

没有设置队列target之前打印如下:

=======================================

task 1 in ----<NSThread: 0x60800007d480>{number = 3, name = (null)}

task 2 in ----<NSThread: 0x60800007d540>{number = 4, name = (null)}

task 3 in ----<NSThread: 0x60800007d600>{number = 5, name = (null)}

task 3 out

task 1 out

task 2 out

dispatch_set_target_queue

在OC中GCD：

 dispatch_set_target_queue   ： 将队列添加到目标队列

这个例子是将一个串行队列和一个并行队列都加到一个串行队列。

OC版源码如下：  

dispatch_queue_t serialQueue = dispatch_queue_create("zy.serialqueue", DISPATCH_QUEUE_SERIAL);

dispatch_queue_t firstQueue = dispatch_queue_create("zy.firstqueue", DISPATCH_QUEUE_SERIAL);

dispatch_queue_t secondQueue = dispatch_queue_create("zy.secondqueue", DISPATCH_QUEUE_CONCURRENT);

dispatch_set_target_queue(firstQueue, serialQueue);

dispatch_set_target_queue(secondQueue, serialQueue);

dispatch_async(firstQueue, ^{

NSLog(@"task 1 in ---- %@",[NSThread currentThread]);

        [NSThread sleepForTimeInterval:3.f];

NSLog(@"task 1 out ---- %@",[NSThread currentThread]);

    });

dispatch_async(secondQueue, ^{

NSLog(@"task 2 in ---- %@",[NSThread currentThread]);

        [NSThread sleepForTimeInterval:2.f];

NSLog(@"task 2 out ---- %@",[NSThread currentThread]);

    });

dispatch_async(secondQueue, ^{

NSLog(@"task 3 in ---- %@",[NSThread currentThread]);

        [NSThread sleepForTimeInterval:1.f];

NSLog(@"task 3 out ---- %@",[NSThread currentThread]);

    });

swift代码 :

func dispatchSetTargetQueueDemo(){

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

let  Queue1  = DispatchQueue(label:"Queue1",target:targetQueue)

let  Queue2  = DispatchQueue(label:"Queue2",attributes:DispatchQueue.Attributes.concurrent,target:targetQueue)

        Queue1.async {

print("task 1 in ----\(Thread.current)")

Thread.sleep(forTimeInterval: 3)

print("task 1 out")

        }

        Queue2.async {

print("task 2 in ----\(Thread.current)")

Thread.sleep(forTimeInterval: 3)

print("task 2 out")

        }

        Queue2.async {

print("task 3 in ----\(Thread.current)")

Thread.sleep(forTimeInterval: 3)

print("task 3 out")

        }

    }

验证一：  如果一个串行队列和一个并行队列，添加到一个串行队列。

结果打印如下：

设置队列target之前打印如下:

task 1 in ----<NSThread: 0x608000264bc0>{number = 3, name = (null)}

task 1 out

task 2 in ----<NSThread: 0x608000264bc0>{number = 3, name = (null)}

task 2 out

task 3 in ----<NSThread: 0x608000264bc0>{number = 3, name = (null)}

task 3 out

结果分析:

  下面的两个队列的任务会在串行队列里，同步执行。

验证二：  如果一个串行队列和一个并行队列，添加到一个并行队列。

结果打印如下：

设置队列target之前打印如下:

task 1 in ----<NSThread: 0x60800026be80>{number = 3, name = (null)}

task 2 in ----<NSThread: 0x60800026bf80>{number = 4, name = (null)}

task 3 in ----<NSThread: 0x60800026c080>{number = 5, name = (null)}

task 1 out

task 3 out

task 2 out

结果分析:

  下面的两个队列的任务会在并行队列里，异步执行。

总结：dispatch_set_target_queue   将队列加入目标队列，并且按照目标队列的顺序执行。如果是串行队列就串行同步执行，并发队列就异步并发执行。

小例源码：

https://github.com/RainManGO/GCD_targetQueueDemo.git