GCD全解-05-dispatch_apply

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/82464766

重复执行某个任务，但是注意这个方法没有办法异步执行
（为了不阻塞线程可以使用dispatch_async()包装一下再执行

* @abstract
 * Submits a block to a dispatch queue for parallel invocation.
   #  提交一个Block到队列并发调用

 * @discussion
 * Submits a block to a dispatch queue for parallel invocation. This function
 * waits for the task block to complete before returning. If the specified queue
 * is concurrent, the block may be invoked concurrently, and it must therefore
 * be reentrant safe.
 *
 * Each invocation of the block will be passed the current index of iteration.
 *
 * @param iterations The number of iterations（反复） to perform.
 *
 * @param queue
 * The dispatch queue to which the block is submitted.
 * The preferred value to pass is DISPATCH_APPLY_AUTO to automatically use
 * a queue appropriate for the calling thread.

void dispatch_apply(size_t iterations, dispatch_queue_t queue, DISPATCH_NOESCAPE void (^block)(size_t));

demo

dispatch_apply(3, dispatch_queue_create("d", NULL), ^(size_t index) {
        NSLog(@"copy-%ld", index);
});
2016-11-05 17:01:38.138 Multithreading[16124:481707] copy-0
2016-11-05 17:01:38.138 Multithreading[16124:481707] copy-1
2016-11-05 17:01:38.138 Multithreading[16124:481707] copy-2


dispatch_apply(3, dispatch_queue_create("c", DISPATCH_QUEUE_CONCURRENT), ^(size_t index) {
        NSLog(@"copy-%ld", index);
});
2016-11-05 17:04:10.798 Multithreading[16153:483197] copy-2
2016-11-05 17:04:10.798 Multithreading[16153:483181] copy-1
2016-11-05 17:04:10.798 Multithreading[16153:483141] copy-0