GCD全解-03-dispatch_after/dispatch_time

版权声明：知识版权是属于全人类的! 欢迎评论与转载!!! https://blog.csdn.net/zhuge1127/article/details/82464566

dispatch_after

延时操作的API，通常Queue会在主线程，但是也可以自定义线程

* @functoin Schedule a block for execution on a given queue at a specified time.
 * @param when
 * A temporal milestone returned by dispatch_time() or dispatch_walltime().

void dispatch_after(dispatch_time_t when, dispatch_queue_t queue, dispatch_block_t block);

* @param context
 * The application-defined context parameter to pass to the function.
 *
 * @param work
 * The application-defined function to invoke on the target queue. The first
 * parameter passed to this function is the context provided to
 * dispatch_after_f().
 * The result of passing NULL in this parameter is undefined.

void dispatch_after_f(dispatch_time_t when, dispatch_queue_t queue, void *_Nullable context,    dispatch_function_t work);

dispatch_time

A somewhat abstract representation of time; 
where zero means "now" and DISPATCH_TIME_FOREVER means "infinity" and every value in between is an opaque encoding.
typedef uint64_t dispatch_time_t;

#define DISPATCH_TIME_NOW (0ull)
#define DISPATCH_TIME_FOREVER (~0ull)

// Create dispatch_time_t relative to the default clock or modify an existing dispatch_time_t.
//An optional dispatch_time_t to add nanoseconds to. If zero is passed, then dispatch_time() will use the result of mach_absolute_time().
dispatch_time_t dispatch_time(dispatch_time_t when, int64_t delta);

常见用法

dispatch_after(dispatch_time(DISPATCH_TIME_NOW,
                                 (int64_t)(60 * NSEC_PER_SEC)),
                   dispatch_get_main_queue(), ^{
    # 主线程执行代码
});

NSLog(@"你好吗?");

dispatch_after(dispatch_time(DISPATCH_TIME_NOW, 3 * NSEC_PER_SEC), dispatch_queue_create("ll", NULL), ^{
       NSLog(@"你好");
});

这里都是一样的,只不过调用的线程种类不一样
2016-11-05 17:10:43.921 Multithreading[16258:488248] 你好吗?
2016-11-05 17:10:47.217 Multithreading[16258:488289] 你好