dispatch_block_t block = ^{

         for (int i = ; i < ; i++) {

             NSLog(@"dispatch_sync:%d", i);

         }

     };

     dispatch_queue_t queue = dispatch_queue_create("FIFO.QUEQE", );

     dispatch_async(queue, block);

     NSLog(@"finish dispatch_asyn");

     dispatch_sync(dispatch_get_main_queue(), ^{

         NSLog(@"sync");

     });

     NSLog(@"finish dispatch_sync");