GCD的使用方法

来源：互联网发布：php中介者模式编辑：程序博客网时间：2024/06/15 15:56
在项目开发中我们用到最多的就是GCD
特总结常用的几点与大家分享
#import "ViewController.h"@interface ViewController (){    /**     *  串行队列     */    dispatch_queue_t _mainQueue;    /**     *  并行队列     */    dispatch_queue_t _globelQueue;}@end@implementation ViewController/* 异步调度和同步调度 异步调度 dispatch_async : 把一个任务添加到某queue后就马上离开,而不管任务在那个queue里的执行状态 同步调度 dispatch_sync : 把一个任务添加到某queue后,等这个任务完成,调用线程才继续执行.  所以,异步调度和同步调度的区别不在于被添加的任务怎样执行,而在于调用线程是否等待任务执行完 */- (void)viewDidLoad {    [super viewDidLoad];    // Do any additional setup after loading the view, typically from a nib.    //    串行队列//    并行队列    //GCD:Grand-Central-Dispatch;        #if 0    /*     死锁     */    NSLog(@"1111111111");    dispatch_sync(dispatch_get_main_queue(), ^{        NSLog(@"222222222222");    });    NSLog(@"33333333333");        只会打印11111111111#endif            _mainQueue = dispatch_get_main_queue();    _globelQueue = dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0);        [self test4];    #if 0    公式：        dispatch_async(_globelQueue, ^{        //请求数据       dispatch_async(_mainQueue, ^{        //刷新UI       });    });#endif    }//A,B,C表示3个任务，A,B,C并行执行- (void)test1{      //A    dispatch_async(_globelQueue, ^{        [self downloadWithUrlString:@"http://d3.s.hjfile.cn/2012/201202_3/43904b09-24e1-4fdb-8b46-d3dba3323278.mp3" string:@"A"];    });    //B    dispatch_async(_globelQueue, ^{        [self downloadWithUrlString:@"http://d3.s.hjfile.cn/2012/201202_3/43904b09-24e1-4fdb-8b46-d3dba3323278.mp3" string:@"B"];    });    //C    dispatch_async(_globelQueue, ^{        [self downloadWithUrlString:@"http://d3.s.hjfile.cn/2012/201202_3/43904b09-24e1-4fdb-8b46-d3dba3323278.mp3" string:@"C"];    });}//A,B并发执行，最后C- (void)test2{    //调度组    dispatch_group_t group = dispatch_group_create();        //A    dispatch_group_async(group, _globelQueue, ^{        [self downloadWithUrlString:@"http://d3.s.hjfile.cn/2012/201202_3/43904b09-24e1-4fdb-8b46-d3dba3323278.mp3" string:@"A"];    });        //B    dispatch_group_async(group, _globelQueue, ^{        [self downloadWithUrlString:@"http://d3.s.hjfile.cn/2012/201202_3/43904b09-24e1-4fdb-8b46-d3dba3323278.mp3" string:@"B"];    });        //1.其他任务都执行完，最后刷新UI    //执行的任务 C    dispatch_group_notify(group, _mainQueue, ^{        //刷新    });        //2.有一个下载需要最后执行    dispatch_group_async(group, _globelQueue, ^{                //执行最后一个任务        //my code                dispatch_async(_mainQueue, ^{            //刷新UI        });    });}//A,B并发执行,然后执行C,最后D,E(一个任务把其他任务分开)- (void)test3{    //barrier需要自定义队列    /*     dispatch_queue_create("队列名字", 串行/并行)     NULL表示DISPATCH_QUEUE_SERIAL          DISPATCH_QUEUE_SERIAL      串行     DISPATCH_QUEUE_CONCURRENT  并行         */        NSString *urlString = @"http://g.hiphotos.baidu.com/image/h%3D768%3Bcrop%3D0%2C0%2C1024%2C768/sign=ad148bd817ce36d3bd04813602c859f5/42166d224f4a20a4b0824bc592529822720ed010.jpg";           dispatch_queue_t customQueue = dispatch_queue_create("com.xxxx.queue", DISPATCH_QUEUE_CONCURRENT);        //A    dispatch_async(customQueue, ^{        [self downloadWithUrlString:urlString string:@"A"];    });    //B    dispatch_async(customQueue, ^{        [self downloadWithUrlString:urlString string:@"B"];    });        //C    dispatch_barrier_async(customQueue, ^{        [self downloadWithUrlString:urlString string:@"C"];    });        //D    dispatch_async(customQueue, ^{        [self downloadWithUrlString:urlString string:@"D"];    });    //E    dispatch_async(customQueue, ^{        [self downloadWithUrlString:urlString string:@"E"];    });}//执行某个任务多少次- (void)test4{    dispatch_apply(5, _globelQueue, ^(size_t t) {        NSLog(@"%@",[NSString stringWithFormat:@"%zu",t]);    });}//只执行一次，一般用在单例- (void)test5{    static dispatch_once_t onceToken;    dispatch_once(&onceToken, ^{            });}//延迟调用- (void)test6{    /*     ull 表示微秒     */    dispatch_after(dispatch_time(DISPATCH_TIME_NOW, (int64_t)(3 * NSEC_PER_SEC)), dispatch_get_main_queue(), ^{            });}- (void)downloadWithUrlString:(NSString *)urlString string:(NSString *)string{    NSLog(@"开始下载 -- %@",string);    NSData *data = [NSData dataWithContentsOfURL:[NSURL URLWithString:urlString]];    sleep(2);    NSLog(@"下载完成 -- %@",string);}- (void)didReceiveMemoryWarning {    [super didReceiveMemoryWarning];    // Dispose of any resources that can be recreated.}@end
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