GCD

//dispatch_barrier_async使用在并行环境下，
//dispatch_barrier_async添加的任务会在之前的block全部运行完毕之后，才会继续执行，保证线程安全保证对非线程安全的对象进行正确的操作。
//运行完dispatch_barrier_async才会执行后面的任务
//dispatch_barrier_async所在的线程跟前一个任务是同一线程

//延迟执行
dispatch_after(dispatch_time(DISPATCH_TIME_NOW,(int64_t)(5*NSEC_PER_SEC)),dispatch_get_main_queue,dispatch_get_main_queue(),^{
NSLog(@"选择性队列延迟5秒执行");
})
//自定义并行队列
dispatch_queue_t queue=dispatch_queue_create("duoduo",DISPATCH_QUEUE_CONCURRENT);
dispatch_async(queue,^{
NSLog(@"dispatch_async-1-%@",[NSThread currentThread]);
});
dispatch_async(queue,^{
NSLog(@"dispatch_async-2-%@",[NSTread currentThread]);
});
dispatch_barrier_async(queue,^{
NSLog(@"dispatch_barrier_async-%@",[NSTread currentThread]);
});
dispatch_async(queue,^{
NSLog(@"dispatch_async-3-%@",[NSThread currentThread]);
});
dispatch_async(queue,^{
NSLog(@"dispatch_async-4-%@",[NSThread currentThread]);
});

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