如果想在dispatch_queue中所有的任務(wù)執(zhí)行完成后在做某種操作，在串行隊(duì)列中，可以把該操作放到最后一個(gè)任務(wù)執(zhí)行完成后繼續(xù)，但是在并行隊(duì)列中怎么做呢。這就有dispatch_group 成組操作。

dispatch_queue_t dispatchQueue = dispatch_queue_create("ted.queue.next", DISPATCH_QUEUE_CONCURRENT);

dispatch_group_t dispatchGroup=dispatch_group_create();

dispatch_group_async(dispatchGroup, dispatchQueue,^(){

NSLog(@"dispatch-1");

});

dispatch_group_async(dispatchGroup, dispatchQueue,^(){

NSLog(@"dspatch-2");

});

dispatch_group_notify(dispatchGroup, dispatch_get_main_queue(),^(){

NSLog(@"end");

});