iOS多线程NSThread/GCD/NSOperation区别和使用

 全局队列:
 {
    同步:不开
    异步:开N条
 }
 
 主队列(奇葩):
 {
        同步:卡死,不要用
        异步:不开,因为他有主线程
 }
 
 /**
    开不开线程线程由任务是同步还是异步
        同步:打死都不开
        异步:除了主队列,都开,开多少条,由我们的队列的类型来决定
 */

    //一般下载,可能会下载多个
    dispatch_async(dispatch_get_global_queue(0, 0), ^{
        NSLog(@"downLoad----%@",[NSThread currentThread]);
        //去做耗时间的操作
        
        //下载图像...最后得到一个UIImage
        
        //去主线程更新UI
        dispatch_async(dispatch_get_main_queue(), ^{
            NSLog(@"updateUI----%@",[NSThread currentThread]);
        });
        
    });

- (void)viewDidLoad {
    [super viewDidLoad];
    // Do any additional setup after loading the view, typically from a nib.
    
    //创建一个并发的队列
    /**
        注意:如果你用了dispatch_barrier_async必须要用我们自己创建的并发队列,而不能用全局队列
     */
    _concurrentQueue = dispatch_queue_create("com.yun", DISPATCH_QUEUE_CONCURRENT);
    
    //循环去请求20个图片资源
    for (int i=0; i<20; ++i) {
        [self loadPic:i];
    }
}

- (void)loadPic:(int)i{
    //模拟网络,通过URL去访问Bundle里面的图片
    dispatch_async(_concurrentQueue, ^{
        [NSThread sleepForTimeInterval:1.0];
        
        NSString *fileName = [NSString stringWithFormat:@"%02d.jpg",i%10+1];
        
        //1.URL
        NSURL *url =[[NSBundle mainBundle] URLForResource:fileName withExtension:nil];
        
        //2.去Bundle里面加载我们的图片二进制数据
        NSData *data =[NSData dataWithContentsOfURL:url];
        
        //3.将图片的二进制数据,转成UIImage对象
        UIImage *image = [UIImage imageWithData:data];
        
        
        //4.将我们的图像添加到photoList数组中去
        NSLog(@"%@----%d",[NSThread currentThread],i);
        
        dispatch_barrier_async(_concurrentQueue, ^{
            [self.photoList addObject:image];
        });
    });
}

/**
    1.登录
    2.付费
    3.下载
    4.通知用户
 
    1.依赖的代码,必须放在添加任务前
    2.不要造成循环依赖,iOS7之前是直接崩,iOS8,不调度了
 */
- (void)depencyDemo{
    NSLog(@"%s",__FUNCTION__);
    
    NSBlockOperation *login = [NSBlockOperation blockOperationWithBlock:^{
        NSLog(@"%@----login",[NSThread currentThread]);
    }];
    
    NSBlockOperation *notifyUser = [NSBlockOperation blockOperationWithBlock:^{
        NSLog(@"%@----notifyUser",[NSThread currentThread]);
    }];
    
    NSBlockOperation *downLoad = [NSBlockOperation blockOperationWithBlock:^{
        NSLog(@"%@----downLoad",[NSThread currentThread]);
    }];
    
    NSBlockOperation *pay = [NSBlockOperation blockOperationWithBlock:^{
        NSLog(@"%@----pay",[NSThread currentThread]);
    }];
    
    NSOperationQueue *mainQueue = [NSOperationQueue mainQueue];
    
    //GCD,同步,串行队列
    //NSOperation,addDependency就是表示我这个任务,要依赖于哪个任务执行完
    [downLoad addDependency:pay];
    [pay addDependency:login];
    [notifyUser addDependency:downLoad];
    //[login addDependency:downLoad];//???
    
    //将任务添加到`队列`中去
//    [mainQueue addOperation:login];
//    [mainQueue addOperation:notifyUser];
//    [self.concurrentQueue addOperation:downLoad];
//    [mainQueue addOperation:pay];
    // 注意download是放在异步线程里的
     [self.concurrentQueue addOperation:downLoad];
    
    //YES,同步,       主队列千万不要和同步搞在一起
    [mainQueue addOperations:@[login,notifyUser,pay] waitUntilFinished:NO];
    
}

[ViewController depencyDemo]
<NSThread: 0x7fa88a707320>{number = 1, name = main}----login
<NSThread: 0x7fa88a707320>{number = 1, name = main}----pay
<NSThread: 0x7fa88a4bf850>{number = 2, name = (null)}----downLoad
<NSThread: 0x7fa88a707320>{number = 1, name = main}----notifyUser

    //1.创建一个并发队列
    NSOperationQueue *queue = [[NSOperationQueue alloc] init];
    
    //2.创建任务,并将其添加到`并发队列中`
    [queue addOperationWithBlock:^{
        NSLog(@"login===>%@",[NSThread currentThread]);
        
        [NSThread sleepForTimeInterval:2.0];
        
        //去主线程更新UI
        [[NSOperationQueue mainQueue] addOperationWithBlock:^{
            [NSThread sleepForTimeInterval:3.0];
            //更新UI的代码
            NSLog(@"%@===>",[NSThread currentThread]);
        }];
    }];