iOS 多线程与线程锁

最新推荐文章于 2019-08-18 17:17:34 发布

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最新推荐文章于 2019-08-18 17:17:34 发布

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本文链接：https://blog.youkuaiyun.com/linpeng_1/article/details/38050859

</pre><pre name="code" class="html"><span style="font-size:18px;">区别</span>

    dispatch_async(dispatch_get_global_queue(0, 0), ^{
        // 处理耗时操作的代码块...
        UIImage *image = [UIImage imageNamed:@"bb.jpg"];
        UIImageView *imageV = [[UIImageView alloc] initWithFrame:CGRectMake(0, 0, 160, 240)];
        [imageV setImage:image];
        [self.view addSubview:imageV];
        sleep(3);
        //通知主线程刷新
        dispatch_async(dispatch_get_main_queue(), ^{
            //回调或者说是通知主线程刷新，
            
            NSLog(@"update main");
        });
        
    });

以上代码在子线程添加视图要许久（大于3秒）之后才能在UI上显示图片

===========================================================================================
    dispatch_async(dispatch_get_global_queue(0, 0), ^{
        // 处理耗时操作的代码块...
        UIImage *image = [UIImage imageNamed:@"bb.jpg"];
        UIImageView *imageV = [[UIImageView alloc] initWithFrame:CGRectMake(0, 0, 160, 240)];
        [self.view addSubview:imageV];
        sleep(3);
        //通知主线程刷新
        dispatch_async(dispatch_get_main_queue(), ^{
            //回调或者说是通知主线程刷新，
            [imageV setImage:image];
            NSLog(@"update main");
        });
        
    });

以上代码在子线程添加视图然后3秒后通知主线程更新UI（正常做法）

[NSThread detachNewThreadSelector:@selector(aa) toTarget:self withObject:nil];

-(void)aa
{
    sleep(3);
    UIImage *image = [UIImage imageNamed:@"bb.jpg"];
    UIImageView *imageV = [[UIImageView alloc] initWithFrame:CGRectMake(0, 0, 160, 240)];
    if(image!=nil)
    {
        //跟新主线程（线程的通信）
        [self performSelectorOnMainThread:@selector(updateUI:) withObject:image waitUntilDone:YES];
    }      [self.view addSubview:imageV];
}

以上效果类似于第二种

开启一个线程：dispatch_async

全局线程队列：dispatch_get_global_queue(0, 0)

优先级：2 ，0， -2

主线程： dispatch_get_main_queue()

线程锁

    //线程1
    dispatch_async(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0), ^{
         sleep(4);
       [self method1];
    });
    //线程2
    dispatch_async(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0), ^{
         sleep(1);
        [self method2];
    });

以上代码的结果：

2014-07-22 21:23:35.663 demo[13769:3603] method2

2014-07-22 21:23:38.663 demo[13769:3503] method1

  NSLock *lock = [[NSLock alloc] init];
    dispatch_async(dispatch_get_global_queue(0,0), ^{
        @synchronized(lock){
            sleep(4);
            [self method1];
        }
        @synchronized(lock){
            sleep(1);
            [self method2];
        }
    });

以上代码结果：

2014-07-22 21:24:17.498 demo[13787:3503] method1

2014-07-22 21:24:18.500 demo[13787:3503] method2

NSLock

NSLock *lock = [[NSLockalloc]init];

//线程1

dispatch_async(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT,0), ^{

sleep(4);

[locklock];

[selfmethod1];

[lockunlock];

sleep(1);

[locklock];

[selfmethod2];

[lockunlock];

});

以上代码结果：

2014-07-22 21:27:22.029 demo[13837:3503] method1

2014-07-22 21:27:23.030 demo[13837:3503] method2

：

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

NSLog(@"延迟2秒调用");

});

/* 1.dispatch_async 异步处理好使的操作 */

//获取全局队列（三种）

dispatch_queue_t golbalQ =dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT,0);

dispatch_queue_t mainQ =dispatch_get_main_queue();

dispatch_async(dispatch_get_global_queue(0,0), ^{

NSLog(@"开启子线程:dispatch_get_global_queue");

sleep(3);

dispatch_async(dispatch_get_main_queue(), ^{

NSLog(@"更新主线程:dispatch_get_main_queue");

});

2、dispatch_group_async的使用

dispatch_group_async可以实现监听一组任务是否完成，完成后得到通知执行其他的操作。这个方法很有用，比如你执行三个下载任务，当三个任务都下载完成后你才通知界面说完成的了

dispatch_group_t group =dispatch_group_create();

dispatch_queue_t queue =dispatch_get_global_queue(0,0);

dispatch_group_async(group, queue, ^{

sleep(1);

NSLog(@"group1-随机执行");//随机执行

});

dispatch_group_async(group, queue, ^{

sleep(1);

NSLog(@"group2-随机执行");//随机执行

});

dispatch_group_async(group, queue, ^{

sleep(1);

NSLog(@"group3-随机执行");//随机执行

});

dispatch_group_notify(group, queue, ^{

NSLog(@"update(只有等上面三个group1,group2,group3执行完毕之后才会调用)");

});

3、dispatch_barrier_async的使用

dispatch_barrier_async是在前面的任务执行结束后它才执行，而且它后面的任务等它执行完成之后才会执行

// dispatch_queue_t queueBarrier = dispatch_get_global_queue(0, 0);

//queueBarrier这个队列不能是全局的dispatch_get_global_queue(0, 0)必须自己定义一个队列

dispatch_queue_t queueBarrier =dispatch_queue_create("gcdtest.rongfzh.yc",DISPATCH_QUEUE_CONCURRENT);

dispatch_async(queueBarrier, ^{

sleep(1);

NSLog(@"b1随机执行");

});

dispatch_async(queueBarrier, ^{

sleep(1);

NSLog(@"b2随机执行");

});

dispatch_barrier_async(queueBarrier, ^{

sleep(0);

NSLog(@"dispatch_barrier_async只有等之前做的做完才会执行后面的线程至于它执行完毕后才执行");

});

dispatch_async(queueBarrier, ^{

sleep(1);

NSLog(@"b3随机执行");

});

4、dispatch_apply

执行某个代码片段N次。

dispatch_apply(5,dispatch_get_global_queue(0,0), ^(size_t index) {

sleep(1);

NSLog(@"dispatch_apply执行某个代码片段5次 %ld",index);

});

/**

* 只会执行一次

static dispatch_once_t onceToken;

dispatch_once(&onceToken, ^{

sleep(1);

NSLog(@"dispatch_once 只会执行一次");

});

//创建一个信号量：2

dispatch_semaphore_t semaphores = dispatch_semaphore_create(2);

for (int i = 0; i<10; i++) {

dispatch_async(dispatch_get_global_queue(0, 0), ^{

NSLog(@"==== %d",i);

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

//释放资源发出信号量

//dispatch_semaphore_signal(semaphores);

});

}

//等待资源

dispatch_semaphore_wait(semaphores, DISPATCH_TIME_FOREVER);

//当没有资源释放的时候线程就堵住了

dispatch_semaphore_wait(semaphores, DISPATCH_TIME_FOREVER);