IOS 并发

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主线程 main Thread

ios中我们写的代码是被Event来调用
主线程 有一个 run loop用于接受Events
主线程 用于处理界面接触的Event
Event处理代码运行时候会阻塞主线程

三种实现线程的方法

1. //进入后台进程 执行一个耗时的方法
   [self performSelectorInBackground:@selector(backWork) withObject:nil];
   //后台执行的方法
   -(void) backWork{
       NCLog(@"background thread %@",[NSThread currentThread]); 
       sleep(5);
       //回到主线程 
       [self performSelectorOnMainThread:@selector(mainWork) withObject:nil waitUntilDone:NO];
   }
   
   -(void) mainWork{
       NCLog(@"main  thread %@",[NSThread currentThread]);
   [self.indicator stopAnimating];
   }
   

2. NSBlockOperation

 //定义 一个task
     NSBlockOperation *op=[NSBlockOperation blockOperationWithBlock:^{
        NCLog(@"NSBlockOperation xxx....");
         sleep(5);
        [self performSelectorOnMainThread:@selector(mainWork) withObject:nil waitUntilDone:NO];
    }];
    //把task 加入到执行队列
    NSOperationQueue *queue = [[NSOperationQueue alloc]init];
    [queue addOperation:op];

1. GCD 大中枢 相对NSOperation是更底层的框架.
   用了block代码更加简洁

```
dispatch_async(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0), ^{
NCLog(@"dispatch_async xxx....");
[self.indicator startAnimating];
sleep(5); dispatch_async(dispatch_get_main_queue(), ^{
[self mainWork];
[self.indicator stopAnimating];

    });
});

```

参考 http://blog.csdn.net/totogo2010/article/details/8016129