GCD--队列的类型和执行任务方式的四种的排列组合

串行队列

• 串行队列同步执行

- (IBAction)SerialQueueSync:(id)sender {    //1.创建串行队列    dispatch_queue_t queue = dispatch_queue_create("FirstSerialQueue", DISPATCH_QUEUE_SERIAL);    //2.提交任务到队列中(block)    //同步执行任务    dispatch_sync(queue, ^{        //任务逻辑        for (int i = 0; i < 10; i++) {            [NSThread sleepForTimeInterval:1];            NSLog(@"++++++++++%@", [NSThread currentThread]);        }    });    NSLog(@"第一个打印完毕");    //第二个任务    dispatch_sync(queue, ^{        for (int i = 0; i < 10; i++) {            [NSThread sleepForTimeInterval:1];            NSLog(@"----------%@", [NSThread currentThread]);        }    });    NSLog(@"第二个打印完毕");}

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• 串行队列异步执行

- (IBAction)SerialQueueAsync:(id)sender {    dispatch_queue_t queue = dispatch_queue_create("SecondSerialQueue", DISPATCH_QUEUE_SERIAL);    dispatch_async(queue, ^{        for (int i = 0; i < 10; i++) {            [NSThread sleepForTimeInterval:1];            NSLog(@"++++++++++%@", [NSThread currentThread]);        }    });    NSLog(@"第一个打印完毕");    dispatch_async(queue, ^{        for (int i = 0; i < 10; i++) {            [NSThread sleepForTimeInterval:1];            NSLog(@"----------%@", [NSThread currentThread]);        }    });    NSLog(@"第二个打印完毕");}

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并行队列

• 并行队列同步执行

//几乎不用这种组合(串行队列+同步执行结果一样)- (IBAction)concurrentQueueSync:(id)sender {    dispatch_queue_t queue = dispatch_queue_create("FirstConcurrentQueue", DISPATCH_QUEUE_CONCURRENT);    dispatch_sync(queue, ^{        for (int i = 0; i < 10; i++) {            [NSThread sleepForTimeInterval:1];            NSLog(@"++++++++++%@", [NSThread currentThread]);        }    });    NSLog(@"第一个打印完毕");    dispatch_sync(queue, ^{        for (int i = 0; i < 10; i++) {            [NSThread sleepForTimeInterval:1];            NSLog(@"----------%@", [NSThread currentThread]);        }    });    NSLog(@"第二个打印完毕");}

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• 并行队列异步执行

- (IBAction)concurrentQueuAsync:(id)sender {    dispatch_queue_t queue = dispatch_queue_create("SecondConcurrentQueue", DISPATCH_QUEUE_CONCURRENT);    dispatch_async(queue, ^{        for (int i = 0; i < 10; i++) {            [NSThread sleepForTimeInterval:1];            NSLog(@"++++++++++%@", [NSThread currentThread]);        }    });    NSLog(@"第一个打印完毕");    dispatch_async(queue, ^{        for (int i = 0; i < 10; i++) {            [NSThread sleepForTimeInterval:1];            NSLog(@"----------%@", [NSThread currentThread]);        }    });    NSLog(@"第二个打印完毕");}

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全局队列

• 全局队列异步执行

//和并行队列异步执行一模一样- (IBAction)globalQueueAsync:(id)sender {    //获取系统默认创建的全局队列(参数一:给定队列的优先级)    dispatch_queue_t queue = dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0);    //提交任务到全局队列中    dispatch_async(queue, ^{        for (int i = 0; i < 10; i++) {            [NSThread sleepForTimeInterval:1];            NSLog(@"++++++++++++:%@",[NSThread currentThread]);        }    });    NSLog(@"第一个打印完毕");    dispatch_async(queue, ^{        for (int i = 0; i < 10; i++) {            [NSThread sleepForTimeInterval:1];            NSLog(@"----------%@", [NSThread currentThread]);        }    });    NSLog(@"第二个打印完毕");}

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主队列

• 主队列异步执行

- (IBAction)mainQueueAsync:(id)sender {    //注意:所有主队列中的任务都是由主线程完成    //获取系统默认创建好的主队列    dispatch_queue_t queue = dispatch_get_main_queue();    //提交任务到主队列中    dispatch_async(queue, ^{        for (int i = 0; i < 10; i++) {            [NSThread sleepForTimeInterval:1];            NSLog(@"++++++++++%@", [NSThread currentThread]);        }    });    NSLog(@"第一个打印完毕");    dispatch_async(queue, ^{        for (int i = 0; i < 10; i++) {            [NSThread sleepForTimeInterval:1];            NSLog(@"----------%@", [NSThread currentThread]);        }    });    NSLog(@"第二个打印完毕");}

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• 主队列同步执行

//死锁问题(任务不要放到主队列中并且同步执行)- (IBAction)mainQueueSync:(id)sender {    //主队列同步执行    NSLog(@"任务一");    dispatch_sync(dispatch_get_main_queue(), ^{        NSLog(@"任务二");    });    NSLog(@"任务三");}