GCD 相关用法

1.线程间通讯

{

    //1.开子线程下载图片
    //创建队列(并发)
    dispatch_queue_t queue = dispatch_get_global_queue(0, 0);
    
    //异步函数
    dispatch_async(queue, ^{
        
        //1.获取url地址
        NSURL *url = [NSURL URLWithString:@"imageUrl"];
        
        //2.下载图片
        NSData *data = [NSData dataWithContentsOfURL:url];

        //3.把二进制数据转换成图片
        UIImage *image = [UIImage imageWithData:data];
        
        NSLog(@"----%@",[NSThread currentThread]);
        
        dispatch_sync(dispatch_get_main_queue(), ^{
            self.imageView.image = image;
            NSLog(@"+++%@",[NSThread currentThread]);
        });
    });
}

2.队列组

-(void)group
{
    //下载图片1
    
    //创建队列组
    dispatch_group_t group =  dispatch_group_create();
    
    //1.开子线程下载图片
    //创建队列(并发)
    dispatch_queue_t queue = dispatch_get_global_queue(0, 0);
    
    dispatch_group_async(group, queue, ^{
        //1.获取url地址
        NSURL *url = [NSURL URLWithString:@"http://www.huabian.com/uploadfile/2015/0914/20150914014032274.jpg"];
        
        //2.下载图片
        NSData *data = [NSData dataWithContentsOfURL:url];
        
        //3.把二进制数据转换成图片
        self.image1 = [UIImage imageWithData:data];
        
        NSLog(@"1---%@",self.image1);
    });
  
    //下载图片2
    dispatch_group_async(group, queue, ^{
        //1.获取url地址
        NSURL *url = [NSURL URLWithString:@"http://img1.3lian.com/img2011/w12/1202/19/d/88.jpg"];
        
        //2.下载图片
        NSData *data = [NSData dataWithContentsOfURL:url];
        
        //3.把二进制数据转换成图片
        self.image2 = [UIImage imageWithData:data];
        NSLog(@"2---%@",self.image2);
        
    });
    
    //合成
    dispatch_group_notify(group, queue, ^{
        
        //开启图形上下文
        UIGraphicsBeginImageContext(CGSizeMake(200, 200));
        
        //画1
        [self.image1 drawInRect:CGRectMake(0, 0, 200, 100)];
        
        //画2
        [self.image2 drawInRect:CGRectMake(0, 100, 200, 100)];
        
        //根据图形上下文拿到图片
        UIImage *image =  UIGraphicsGetImageFromCurrentImageContext();
        
        //关闭上下文
        UIGraphicsEndImageContext();
        
        dispatch_async(dispatch_get_main_queue(), ^{
            self.imageView.image = image;
            NSLog(@"%@--刷新UI",[NSThread currentThread]);
        });
    });
}

3.dispatch_apply

-(void)applay
{
//    for (NSInteger i=0; i<10; i++) {
//        NSLog(@"%zd--%@",i,[NSThread currentThread]);
//    }
    
    //创建队列(并发队列)
    dispatch_queue_t queue = dispatch_queue_create("com.downloadqueue", DISPATCH_QUEUE_CONCURRENT);
    /*
     第一个参数:迭代的次数
     第二个参数:在哪个队列中执行
     第三个参数:block要执行的任务
     */
    dispatch_apply(10, queue, ^(size_t index) {
        NSLog(@"%zd--%@",index,[NSThread currentThread]);
    });
}

4.delay

-(void)delay
{
    NSLog(@"----");
    //表名2秒钟之后调用run
//    [self performSelector:@selector(run) withObject:nil afterDelay:2.0];
    
//    [NSTimer scheduledTimerWithTimeInterval:2.0 target:self selector:@selector(run) userInfo:nil repeats:YES];
    
    /*
     第一个参数:延迟时间
     第二个参数:要执行的代码
     */
    dispatch_after(dispatch_time(DISPATCH_TIME_NOW, (int64_t)(2.0 * NSEC_PER_SEC)), dispatch_get_global_queue(0, 0), ^{
        NSLog(@"---%@",[NSThread currentThread]);
    });
    
}

5.单例

{
    static dispatch_once_t onceToken;
    dispatch_once(&onceToken, ^{
        NSLog(@"+++++++++");
    });
}

6.栅栏函数

-(void)barrier
{
    //1.创建队列(并发队列)
    dispatch_queue_t queue = dispatch_queue_create("com.downloadqueue", DISPATCH_QUEUE_CONCURRENT);
    
    dispatch_async(queue, ^{
        
        for (NSInteger i = 0; i<10; i++) {
            NSLog(@"%zd-download1--%@",i,[NSThread currentThread]);
        }
    });
    
    dispatch_async(queue, ^{
        
        for (NSInteger i = 0; i<10; i++) {
            NSLog(@"%zd-download2--%@",i,[NSThread currentThread]);
        }
    });
    
    //栅栏函数
    dispatch_barrier_async(queue, ^{
        NSLog(@"我是一个栅栏函数");
    });
    
    dispatch_async(queue, ^{
        
        for (NSInteger i = 0; i<10; i++) {
            NSLog(@"%zd-download3--%@",i,[NSThread currentThread]);
        }
    });
    
    dispatch_async(queue, ^{
        
        for (NSInteger i = 0; i<10; i++) {
            NSLog(@"%zd-download4--%@",i,[NSThread currentThread]);
        }
    });
}