iOS GCD笔记

串行队列

dispatch_queue_t queue = dispatch_queue_create("testQueue", DISPATCH_QUEUE_SERIAL);

并发队列

dispatch_queue_t queue = dispatch_queue_create("testQueue2", DISPATCH_QUEUE_CONCURRENT);

主队列

dispatch_queue_t mainQueue = dispatch_get_main_queue();

全局并发队列

dispatch_queue_t queue = dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0);

同步执行

dispatch_sync(queue, ^{
        //这里放同步执行任务代码
    });

异步执行

dispatch_async(queue, ^{
        //这里放异步执行任务代码
    });

同步+并发队列 = 没有开启新线程,串行执行任务 sync Concurrent
同步+串行队列 = 没有开启新线程,串行执行任务 sync Serial

异步+并发队列 = 有开启新线程,并发执行任务 async Concurrent
异步+串行队列 = 有开启新线程(1条),串行执行任务 async Serial

同步+主队列 = 主线程调用:死锁 其他线程:没有开启新线程,串行执行任务
异步+主队列 = 没有开启新线程,串行执行任务

同步+并发队列(没有开启新线程,串行执行任务)

- (void)syncConcurrent {
    dispatch_queue_t queue = dispatch_queue_create("syncConcurrent", DISPATCH_QUEUE_CONCURRENT);
    dispatch_sync(queue, ^{
        for (int i = 0; i < 2; i++) {
            [NSThread sleepForTimeInterval:2];//模拟耗时操作
            NSLog(@"1--%@",[NSThread currentThread]);
        }
    });
    dispatch_sync(queue, ^{
        for (int i = 0; i < 2; i++) {
            [NSThread sleepForTimeInterval:2];
            NSLog(@"2--%@",[NSThread currentThread]);
        }
    });
    dispatch_sync(queue, ^{
        for (int i = 0; i < 2; i++) {
            [NSThread sleepForTimeInterval:2];
            NSLog(@"3--%@",[NSThread currentThread]);
        }
    });
    NSLog(@"end");
}

同步+串行(没有开启新线程,串行执行任务)

- (void)syncSerial {
    dispatch_queue_t queue = dispatch_queue_create("syncSerial", DISPATCH_QUEUE_SERIAL);
    dispatch_sync(queue, ^{
        for (int i = 0; i < 2; i++) {
            [NSThread sleepForTimeInterval:2];
            NSLog(@"1--%@",[NSThread currentThread]);
        }
    });
    dispatch_sync(queue, ^{
        for (int i = 0; i < 2; i++) {
            [NSThread sleepForTimeInterval:2];
            NSLog(@"2--%@",[NSThread currentThread]);
        }
    });
    dispatch_sync(queue, ^{
        for (int i = 0; i < 2; i++) {
            [NSThread sleepForTimeInterval:2];
            NSLog(@"3--%@",[NSThread currentThread]);
        }
    });
    NSLog(@"end");
}

异步+并发(可开启多个线程,任务交替(同时)执行)

- (void)asyncConcurrent {
    dispatch_queue_t queue = dispatch_queue_create("asyncConcurrent", DISPATCH_QUEUE_CONCURRENT);
    dispatch_async(queue, ^{
        for (int i = 0; i < 2; i++) {
            [NSThread sleepForTimeInterval:2];
            NSLog(@"1--%@",[NSThread currentThread]);
        }
    });
    dispatch_async(queue, ^{
        for (int i = 0; i < 2; i++) {
            [NSThread sleepForTimeInterval:2];
            NSLog(@"2--%@",[NSThread currentThread]);
        }
    });
    dispatch_async(queue, ^{
        for (int i = 0; i < 2; i++) {
            [NSThread sleepForTimeInterval:2];
            NSLog(@"3--%@",[NSThread currentThread]);
        }
    });
    NSLog(@"end");
}

异步+串行(有开启新线程(1条),串行执行任务)

- (void)asyncSerial {
    dispatch_queue_t queue = dispatch_queue_create("asyncSerial", DISPATCH_QUEUE_SERIAL);
    dispatch_async(queue, ^{
        for (int i = 0; i < 2; i++) {
            [NSThread sleepForTimeInterval:2];
            NSLog(@"1--%@",[NSThread currentThread]);
        }
    });
    dispatch_async(queue, ^{
        for (int i = 0; i < 2; i++) {
            [NSThread sleepForTimeInterval:2];
            NSLog(@"2--%@",[NSThread currentThread]);
        }
    });
    dispatch_async(queue, ^{
        for (int i = 0; i < 2; i++) {
            [NSThread sleepForTimeInterval:2];
            NSLog(@"3--%@",[NSThread currentThread]);
        }
    });
    NSLog(@"end");
}

同步执行+主队列(主线程调用:死锁)

- (void)syncMain {
    dispatch_queue_t queue = dispatch_get_main_queue();
    dispatch_sync(queue, ^{
        for (int i = 0; i < 2; i++) {
            [NSThread sleepForTimeInterval:2];
            NSLog(@"1--%@",[NSThread currentThread]);
        }
        for (int i = 0; i < 2; i++) {
            [NSThread sleepForTimeInterval:2];
            NSLog(@"2--%@",[NSThread currentThread]);
        }
        for (int i = 0; i < 2; i++) {
            [NSThread sleepForTimeInterval:2];
            NSLog(@"3--%@",[NSThread currentThread]);
        }
    });
    NSLog(@"end");
}

同步执行+主队列(其他线程调用:没有开启新线程,串行执行任务)

- (void)syncMain2 {
    [NSThread detachNewThreadSelector:@selector(syncMain) toTarget:self withObject:nil];
}

异步执行+主队列(只在主线程中执行任务,执行完一个任务,再执行下一个任务)

- (void)asyncMain {
    dispatch_queue_t queue = dispatch_get_main_queue();
    dispatch_async(queue, ^{
        for (int i = 0; i < 2; i++) {
            [NSThread sleepForTimeInterval:2];
            NSLog(@"1--%@",[NSThread currentThread]);
        }
        for (int i = 0; i < 2; i++) {
            [NSThread sleepForTimeInterval:2];
            NSLog(@"2--%@",[NSThread currentThread]);
        }
        for (int i = 0; i < 2; i++) {
            [NSThread sleepForTimeInterval:2];
            NSLog(@"3--%@",[NSThread currentThread]);
        }
    });
    NSLog(@"end");
}

GCD线程间的通信

- (void)communication {
    //全局并发队列
    dispatch_queue_t queue = dispatch_get_global_queue(0, 0);
    //主队列
    dispatch_queue_t mainQueue = dispatch_get_main_queue();
    
    dispatch_async(queue, ^{
        for (int i = 0; i < 2; i++) {
            [NSThread sleepForTimeInterval:2];
            NSLog(@"1--%@",[NSThread currentThread]);
        }
        //回主线程
        dispatch_async(mainQueue, ^{
            [NSThread sleepForTimeInterval:2];
            NSLog(@"2--%@",[NSThread currentThread]);
        });
    });
}

栅栏方法 dispatch_barrier_async

- (void)barrier {
    dispatch_queue_t queue = dispatch_queue_create("testQueue", DISPATCH_QUEUE_CONCURRENT);
    
    dispatch_async(queue, ^{
        for (int i = 0; i < 2; i++) {
            [NSThread sleepForTimeInterval:2];
            NSLog(@"1--%@",[NSThread currentThread]);
        }
    });
    dispatch_async(queue, ^{
        for (int i = 0; i < 2; i++) {
            [NSThread sleepForTimeInterval:2];
            NSLog(@"2--%@",[NSThread currentThread]);
        }
    });
    
    dispatch_barrier_async(queue, ^{
        for (int i = 0; i < 2; i++) {
            [NSThread sleepForTimeInterval:2];
            NSLog(@"barrier--%@",[NSThread currentThread]);
        }
    });
    dispatch_async(queue, ^{
        for (int i = 0; i < 2; i++) {
            [NSThread sleepForTimeInterval:2];
            NSLog(@"3--%@",[NSThread currentThread]);
        }
    });
    dispatch_async(queue, ^{
        for (int i = 0; i < 2; i++) {
            [NSThread sleepForTimeInterval:2];
            NSLog(@"4--%@",[NSThread currentThread]);
        }
    });
}

GCD延时执行方法: dispatch_after

- (void)after {
    dispatch_after(dispatch_time(DISPATCH_TIME_NOW, (int64_t)(3.0 * NSEC_PER_SEC)), dispatch_get_main_queue(), ^{
        //3秒后执行
        NSLog(@"after---%@",[NSThread currentThread]);
    });
}

GCD一次性代码

-(void)once {
    static dispatch_once_t onceToken;
    dispatch_once(&onceToken, ^{
        //只执行一次的代码(这里默认是线程安全的)
    });
}

GCD快速迭代

-(void)apply {
    dispatch_queue_t queue = dispatch_get_global_queue(0, 0);
    NSLog(@"apply begin");
    dispatch_apply(6, queue, ^(size_t index) {
        NSLog(@"%zd---%@",index, [NSThread currentThread]);
    });
    NSLog(@"apple end");
}

GCD队列组 dispatch_group
dispatch_group_notify(监听group中任务完成的状态,当所有的任务都执行完成后,追加任务到group中,并执行任务)

- (void)groupNotify {
    dispatch_group_t group = dispatch_group_create();
    dispatch_group_async(group, dispatch_get_global_queue(0, 0), ^{
        for (int i = 0; i < 2; i++) {
            [NSThread sleepForTimeInterval:2];
            NSLog(@"1--%@",[NSThread currentThread]);
        }
    });
    dispatch_group_async(group, dispatch_get_global_queue(0, 0), ^{
        for (int i = 0; i < 2; i++) {
            [NSThread sleepForTimeInterval:2];
            NSLog(@"2--%@",[NSThread currentThread]);
        }
    });
    dispatch_group_notify(group, dispatch_get_main_queue(), ^{
        for (int i = 0; i < 2; i++) {
            [NSThread sleepForTimeInterval:2];
            NSLog(@"3--%@",[NSThread currentThread]);
        }
    });
}

dispatch_group_wait(暂停(阻塞)当前线程,等待指定的group中的任务执行完成后,才会往下继续执行)

- (void)groupWait {
    dispatch_group_t group = dispatch_group_create();
    dispatch_group_async(group, dispatch_get_global_queue(0, 0), ^{
        for (int i = 0; i < 2; i++) {
            [NSThread sleepForTimeInterval:2];
            NSLog(@"1--%@",[NSThread currentThread]);
        }
    });
    dispatch_group_async(group, dispatch_get_global_queue(0, 0), ^{
        for (int i = 0; i < 2; i++) {
            [NSThread sleepForTimeInterval:2];
            NSLog(@"2--%@",[NSThread currentThread]);
        }
    });
    dispatch_group_wait(group, DISPATCH_TIME_FOREVER);
    NSLog(@"group---end");
}

线程安全,使用semaphore加锁

- (void)initTicketStatusSave {
    semaphoreLock = dispatch_semaphore_create(1);
    self.ticketCount = 100;
    
    dispatch_queue_t queue1 = dispatch_queue_create("queue1", DISPATCH_QUEUE_SERIAL);
    dispatch_queue_t queue2 = dispatch_queue_create("queue2", DISPATCH_QUEUE_SERIAL);
    
    __weak typeof(self) weakSelf = self;
    
    dispatch_async(queue1, ^{
        [weakSelf saleTicketNotSafe];
    });
    dispatch_async(queue2, ^{
        [weakSelf saleTicketNotSafe];
    });
}
- (void)saleTicketSafe {
    while (1) {
        //加锁
        dispatch_semaphore_wait(semaphoreLock, DISPATCH_TIME_FOREVER);
        if (self.ticketCount > 0) {
            self.ticketCount--;
            NSLog(@"%@",[NSString stringWithFormat:@"剩余票数 %ld   窗口:%@",(long)self.ticketCount,[NSThread currentThread]]);
        } else {
            NSLog(@"所有票已售完");
            //相当于解锁
            dispatch_semaphore_signal(semaphoreLock);
            break;
        }
        //相当于解锁
        dispatch_semaphore_signal(semaphoreLock);
    }
}

参考:https://www.jianshu.com/p/2d57c72016c6

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