IOS 线程的一些理解与使用

好处
1）使用线程可以把程序中占据时间长的任务放到后台去处理，如图片、视频下载
2）发挥多核处理器的优势，并发执行让系统运行的更快、更流畅，用户体验更好
缺点
1）大量的程序降低代码的可读性
2）更多的线程需要更多的空间
3）当多个线程对同一个资源出现争夺的时候需要注意线程安全问题
线程使用：
1）NSThread(两种创建方式)

[NSThread detachNewThreadSelector:@selector(threadBegin:) toTarget:self withObject:@1];

NSThread *thread1 = [[NSThread alloc] initWithTarget:self selector:@selector(threadBegin:) object:@1];

[thread1 start];

2)NSOperationQueue

    __weak typeof(self) weakSelf = self;

    [[NSOperationQueue new] addOperationWithBlock:^{

        [weakSelf threadBegin:@1];

    }];

    

    NSBlockOperation *op = [NSBlockOperation blockOperationWithBlock:^{

        [weakSelf threadBegin:@2];

    }];

    [op addExecutionBlock:^{

        [weakSelf threadBegin:@3];

    }];

    [op addExecutionBlock:^{

        [NSThread sleepForTimeInterval:1];

        [weakSelf threadBegin:@4];

    }];

    [op addExecutionBlock:^{

        [weakSelf threadBegin:@6];

    }];

    [op start];

3）GCD

 dispatch_async(dispatch_get_global_queue(0, 0), ^{ //异步

 [weakSelf threadBegin:@1];

 });

 

 dispatch_group_t group = dispatch_group_create(); // 异步组合

 dispatch_queue_t queue = dispatch_get_global_queue(0, 0);

 dispatch_group_async(group, queue, ^{

 [weakSelf threadBegin:@2];

 });

 dispatch_group_async(group, queue, ^{

 [weakSelf threadBegin:@3];

 });

 dispatch_group_notify(group, queue, ^{

 [weakSelf threadBegin:@4];

 });

 

 // 异步延时

 dispatch_after(dispatch_time(DISPATCH_TIME_NOW, (int64_t)(2 * NSEC_PER_SEC)), dispatch_get_global_queue(0, 0), ^{

 [weakSelf threadBegin:@5];

 });