/*ios 7 DISPATCH_QUEUE_PRIORITY_HIGH 2  高优先级DISPATCH_QUEUE_PRIORITY_DEFAULT 0 默认优先级DISPATCH_QUEUE_PRIORITY_LOW (-2) 低优先级DISPATCH_QUEUE_PRIORITY_BACKGROUND INT16_MIN 非常低 基本忽略ios 8 用户体验度*  - QOS_CLASS_USER_INTERACTIVE 用户交互*  - QOS_CLASS_USER_INITIATED   用户使用*  - QOS_CLASS_DEFAULT          默认使用*  - QOS_CLASS_UTILITY          使用工具*  - QOS_CLASS_BACKGROUND       后台使用预留参数*/dispatch_async(dispatch_get_global_queue(QOS_CLASS_DEFAULT, 0), ^{NSLog(@"异步");});

/**并发异步 开启异步线程 执行顺序 无序　第一个参数: 线程标识符　第二个参数:DISPATCH_QUEUE_CONCURRENT 并发队列

　　*/
dispatch_queue_t q = dispatch_queue_create(queueName, DISPATCH_QUEUE_CONCURRENT);for (int i = 0; i < 100 ; i ++ ) {dispatch_async(q, ^{NSLog(@"%zd, ----- %zd",i ,[NSThread isMainThread]);});}

/**并发同步 不开启线程 按顺序执行1 线程标识符2 线程状态, DISPATCH_QUEUE_CONCURRENT 并发队列*/dispatch_queue_t q = dispatch_queue_create(queueName, DISPATCH_QUEUE_CONCURRENT);for (int i = 0; i < 100 ; i ++ ) {dispatch_sync(q, ^{NSLog(@"%zd, ----- %zd",i ,[NSThread isMainThread]);});}

/**串行同步 不开启线程 按顺序执行*/dispatch_queue_t q = dispatch_queue_create(queueName, DISPATCH_QUEUE_SERIAL);for (int i = 0; i < 100 ; i ++ ) {dispatch_sync(q, ^{NSLog(@"%zd, ----- %zd",i ,[NSThread isMainThread]);});}

/**串行异步 开启子线程线程 按顺序执行*/dispatch_queue_t q = dispatch_queue_create(queueName, DISPATCH_QUEUE_SERIAL);for (int i = 0; i < 100 ; i ++ ) {dispatch_async(q, ^{NSLog(@"%zd, ----- %zd",i ,[NSThread isMainThread]);});}

    //创建线程dispatch_queue_t q = dispatch_queue_create(queueName, DISPATCH_QUEUE_CONCURRENT);//创建线程组dispatch_group_t g = dispatch_group_create();dispatch_group_async(g, q, ^{});//添加任务到线程组dispatch_group_async(g, q, ^{});dispatch_group_async(g, q, ^{});dispatch_group_async(g, q, ^{});/**所有任务完成在 制定的线程通知任务完成*/dispatch_group_notify(g, dispatch_get_main_queue(), ^{});

/*只执行一次*/static dispatch_once_t onceToken;dispatch_once(&onceToken, ^{NSLog(@"只执行一次线程");});　　//通常应用于创建单例 保证线程安全