iOS之GCD再谈(dispatch_barrier_async)

来源：互联网发布：日本久住英语知乎编辑：程序博客网时间：2024/05/16 04:57

假如有这么一个需求，8个线程，前面4个要并行执行，执行完后执行第5个，然后在并行执行后面3个。

那么就要考虑dispatch_barrier_async了

/* dispatch_barrier_async 作用是在并行队列中，等待前面几个操作并行操作完成，然后执行dispatch_barrier_async中的操作， 然后再恢复并行队列所有的执行状态，继续并行执行 */#import "ViewController.h"@interface ViewController ()@end@implementation ViewController- (void)viewDidLoad{    [super viewDidLoad];        //创建一个并行队列    dispatch_queue_t concurrentQueue=dispatch_queue_create("gujinyue", DISPATCH_QUEUE_CONCURRENT);        dispatch_async(concurrentQueue, ^{               NSLog(@"dispatch_1_begin");        sleep(3);        NSLog(@"dispatch_1_end");    });        dispatch_async(concurrentQueue, ^{                NSLog(@"dispatch_2_begin");        sleep(3);        NSLog(@"dispatch_2_end");    });        dispatch_async(concurrentQueue, ^{                NSLog(@"dispatch_3_begin");        sleep(3);        NSLog(@"dispatch_3_end");    });        dispatch_async(concurrentQueue, ^{                NSLog(@"dispatch_4_begin");        sleep(3);        NSLog(@"dispatch_4_end");    });        dispatch_barrier_async(concurrentQueue, ^{                NSLog(@"dispatch_barrier_begin");        sleep(3);        NSLog(@"dispatch_barrier_end");    });        dispatch_async(concurrentQueue, ^{                NSLog(@"dispatch_5_begin");        sleep(3);        NSLog(@"dispatch_5_end");    });        dispatch_async(concurrentQueue, ^{                NSLog(@"dispatch_6_begin");        sleep(3);        NSLog(@"dispatch_6_end");    });        dispatch_async(concurrentQueue, ^{                NSLog(@"dispatch_7_begin");        sleep(3);        NSLog(@"dispatch_7_end");    });       }@end

最终效果：

2016-03-06 09:22:48.906 iOS 学习_dispatch_barrier[938:19679] dispatch_1_begin2016-03-06 09:22:48.906 iOS 学习_dispatch_barrier[938:19682] dispatch_2_begin2016-03-06 09:22:48.906 iOS 学习_dispatch_barrier[938:19687] dispatch_3_begin2016-03-06 09:22:48.906 iOS 学习_dispatch_barrier[938:19691] dispatch_4_begin2016-03-06 09:22:51.907 iOS 学习_dispatch_barrier[938:19687] dispatch_3_end2016-03-06 09:22:51.907 iOS 学习_dispatch_barrier[938:19679] dispatch_1_end2016-03-06 09:22:51.907 iOS 学习_dispatch_barrier[938:19682] dispatch_2_end2016-03-06 09:22:51.908 iOS 学习_dispatch_barrier[938:19691] dispatch_4_end2016-03-06 09:22:51.908 iOS 学习_dispatch_barrier[938:19691] dispatch_barrier_begin2016-03-06 09:22:54.910 iOS 学习_dispatch_barrier[938:19691] dispatch_barrier_end2016-03-06 09:22:54.911 iOS 学习_dispatch_barrier[938:19691] dispatch_5_begin2016-03-06 09:22:54.911 iOS 学习_dispatch_barrier[938:19682] dispatch_6_begin2016-03-06 09:22:54.911 iOS 学习_dispatch_barrier[938:19679] dispatch_7_begin2016-03-06 09:22:57.913 iOS 学习_dispatch_barrier[938:19682] dispatch_6_end2016-03-06 09:22:57.913 iOS 学习_dispatch_barrier[938:19691] dispatch_5_end2016-03-06 09:22:57.913 iOS 学习_dispatch_barrier[938:19679] dispatch_7_end

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