完整详解GCD系列（三）-dispatch_group

标签：gcd   swift   dispatch_group   dispatch_group_enter   dispatch_group_async   

func dispatch_group_create() -> dispatch_group_t!

func dispatch_group_async(_ group: dispatch_group_t!,
                        _ queue: dispatch_queue_t!,
                        _ block: dispatch_block_t!)

func dispatch_group_enter(_ group: dispatch_group_t!)
func dispatch_group_leave(_ group: dispatch_group_t!)

func dispatch_group_notify(_ group: dispatch_group_t!,
                         _ queue: dispatch_queue_t!,
                         _ block: dispatch_block_t!)

long dispatch_group_wait ( dispatch_group_t group, dispatch_time_t timeout );

class ViewController: UIViewController{    
    override func viewDidLoad(){    
        super.viewDidLoad()    
        var hwcGroup = dispatch_group_create()//创建group
	var globalQueueDefault = dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT,0)//全局队列，这个队列为并行队列
	var userCreateQueue =  dispatch_queue_create("com.test.helloHwc",DISPATCH_QUEUE_SERIAL)//创建一个用户队列，这个队列为串行队列
	downLoadTask1(group: hwcGroup,queue: globalQueueDefault)
	downLoadTask2(group: hwcGroup,queue: userCreateQueue)
	downLoadTask3(group: hwcGroup,queue: userCreateQueue)
	//letresult = dispatch_group_wait(hwcGroup,DISPATCH_TIME_FOREVER)
	dispatch_group_notify(hwcGroup,dispatch_get_main_queue()){
		NSLog("Group tasks are done")
	}
	println("Now viewDidLoad is done")
    }
    func downLoadTask1(#group:dispatch_group_t,queue:dispatch_queue_t){
	dispatch_group_async(group,queue){
		sleep(3)
		NSLog("Task1 is done")
	}
    }
   func downLoadTask2(#group:dispatch_group_t,queue:dispatch_queue_t){
	dispatch_group_async(group,queue){
		sleep(3)
		NSLog("Task2 is done")
	}
    }
   func downLoadTask3(#group:dispatch_group_t,queue:dispatch_queue_t){
	dispatch_group_async(group,queue){
		sleep(3)
		NSLog("Task3 is done")
	}
    }    
    override func didReceiveMemoryWarning(){    
        super.didReceiveMemoryWarning()    
    }    
}

可以看到输出为

Now viewDidLoad is done
Task2 is done
Task1 is done
Task3 is done
Group task is done

这里task1提交到全局队列中，task2和task3提交到用户穿件的串行队列中，所以task1和task2同时输出，task3在task2结束两秒后输出。

如果把注释那行取消，会等待一段时间，再返回，读者可以自己去试验下

三、关于如何使用dispatch_group_enter/dispatch_group_leave如何使用

<pre name="code" class="plain">class ViewController: UIViewController{    
    override func viewDidLoad(){    
        super.viewDidLoad()    
        var hwcGroup = dispatch_group_create()//创建group
	var globalQueueDefault = dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT,0)//全局队列，这个队列为并行队列
	for index:UInt32 in 1...3{
	     dispatch_group_enter(hwcGroup)//提交了一个任务，任务数目加1
		manualDownLoad(index){
		    println("Task\(index) is done")
			dispatch_group_leave(hwcGroup)//完成一个任务，任务数目减1
		}
	}
	let result = dispatch_group_wait(hwcGroup,DISPATCH_TIME_FOREVER)//等待直到完成
	dispatch_group_notify(hwcGroup,dispatch_get_main_queue()){
		println("Group tasks are done")
	}
	println("Now viewDidLoad is done")	
    }
    func manualDownLoad(num:UInt32,block:()->()){
	println("Downloading task\(num)")
	sleep(num)
	block()
    }  
    override func didReceiveMemoryWarning(){    
        super.didReceiveMemoryWarning()    
    }    
}

输出

Downloading task1
Task1 is done
Downloading task2
Task2 is done
Downloading task3
Task3 is done
Now viewDidLoad is done
Group is done

可以看到，同步进行了下载，这里的任务是串行的，实际消耗时间9s。当然，也可以把下载的任务提交到异步队列中

class ViewController: UIViewController{    
    override func viewDidLoad(){    
        super.viewDidLoad()    
        var hwcGroup = dispatch_group_create()//创建group
	var globalQueueDefault = dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT,0)//全局队列，这个队列为并行队列
	for index:UInt32 in 1...3{
	     dispatch_group_enter(hwcGroup)//提交了一个任务，任务数目加1
		manualDownLoad(index,queue:globalQueueDefault){
		    NSLog("Task\(index) is done")
			dispatch_group_leave(hwcGroup)//完成一个任务，任务数目减1
		}
	}
	dispatch_group_notify(hwcGroup,dispatch_get_main_queue()){
		NSLog("Group tasks are done")
	}
	NSLog("Now viewDidLoad is done")	
    }
    func manualDownLoad(num:UInt32,queue:dispatch_queue_t, block:()->()){
	dispatch_async(queue){
	NSLog("Downloading task\(num)")
	sleep(num)
	block()
        }
    }  
    override func didReceiveMemoryWarning(){    
        super.didReceiveMemoryWarning()    
    }    
}

这样的话，输出是

Downloading task1
Downloading task2
Downloading task3
Now viewDidLoad is done
Task1 is done
Task2 is done
Task3 is done

由于三个模拟的下载任务是并行的，所以实际消耗时间3s

完整详解GCD系列（三）-dispatch_group

标签：gcd   swift   dispatch_group   dispatch_group_enter   dispatch_group_async   

原文地址：http://blog.csdn.net/hello_hwc/article/details/41409135