项目开发中的GCD实战应用

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整理一下项目中GCD的应用

GCD是apple提供的一组C语言的API,主要用于实现一些特殊的功能,比如并发编程等,虽然是C语言的接口,但是经过block封装,调用十分方便,因此在项目中应用十分广泛,现在总结一下我个人在项目中的使用.

延迟执行

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NSTimeInterval delayTime = 5;
dispatch_after(dispatch_time(DISPATCH_TIME_NOW, (int64_t)(delayTime * NSEC_PER_SEC)), 	dispatch_get_main_queue(), ^{
        /// do someting on main thread
});

快速创建单例

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+ (instancetype)shareInstance
{
    static id shareInstance = nil;
    static dispatch_once_t onceToken;
    dispatch_once(&onceToken, ^{
        shareInstance = [[self alloc] init];
    });
    return shareInstance;
}

异步执行代码

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dispatch_sync(dispatch_get_global_queue(0, 0), ^{
	// do something ,global queue
	dispatch_sync(dispatch_get_main_queue(), ^{
		// main thread
	});
});

顺序执行代码(相当于使用NSOperationQueue的Dependency)

1,2,3同时执行,4最后打印

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dispatch_group_t serviceGroup = dispatch_group_create();
   
    dispatch_group_enter(serviceGroup);
    dispatch_async(dispatch_get_global_queue(0, 0), ^{
        NSLog(@"1---%@", [NSThread currentThread]);
        dispatch_group_leave(serviceGroup);
    });
   
    dispatch_group_enter(serviceGroup);
    dispatch_async(dispatch_get_global_queue(0, 0), ^{
        NSLog(@"2---%@", [NSThread currentThread]);
        dispatch_group_leave(serviceGroup);
    });
   
    dispatch_group_enter(serviceGroup);
    dispatch_async(dispatch_get_global_queue(0, 0), ^{
        NSLog(@"3---%@", [NSThread currentThread]);
        dispatch_group_leave(serviceGroup);
    });
   
    dispatch_group_notify(serviceGroup, dispatch_get_main_queue(), ^{
        NSLog(@"4----%@", [NSThread currentThread]); 
    });

1,2异步执行完毕再异步执行3,4

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dispatch_queue_t barrierQueue = dispatch_queue_create("jiangdaohong.github.io", DISPATCH_QUEUE_CONCURRENT);
    dispatch_async(barrierQueue, ^(){
        NSLog(@"1");
    });
    dispatch_async(barrierQueue, ^(){
        NSLog(@"2");
    });
    dispatch_barrier_async(barrierQueue, ^(){
        NSLog(@"dispatch_barrier_async test");
    });
    dispatch_async(barrierQueue, ^(){
        NSLog(@"3");
    });
    dispatch_async(barrierQueue, ^(){
        NSLog(@"4");
    });

同步请求

由于NSURLSession没有提供同步请求,可以利用semaphore实现同步请求.

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NSURLSession *session = [NSURLSession sharedSession];
// 创建信号
dispatch_semaphore_t semaphore = dispatch_semaphore_create(0);
NSURLSessionDataTask *task = [session dataTaskWithRequest:request completionHandler:^(NSData *data, NSURLResponse *response, NSError *error) {
    // 设置信号量
    dispatch_semaphore_signal(semaphore);
}];
[task resume];
// 等待
dispatch_semaphore_wait(semaphore, DISPATCH_TIME_FOREVER);

定时器(NSTimer不准)

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//倒计时时间
__block int timeout = 60;
dispatch_queue_t queue = dispatch_get_global_queue(0, 0);
dispatch_source_t timer = dispatch_source_create(DISPATCH_SOURCE_TYPE_TIMER, 0, 0, queue);
// 执行间隔1s
dispatch_source_set_timer(timer, dispatch_walltime(NULL, 0),1.0 * NSEC_PER_SEC, 0);
dispatch_source_set_event_handler(timer, ^{
    if(timeout <= 0){
        // 倒计时结束，关闭
        dispatch_source_cancel(timer);
        dispatch_async(dispatch_get_main_queue(), ^{
            // 主线程刷新UI
        });
    } else {
        int minutes = timeout / 60;
        int seconds = timeout % 60;
        dispatch_async(dispatch_get_main_queue(), ^{
            // 主线程刷新UI
        });
        timeout--;
    }
});
dispatch_resume(timer);