1.使用信号量
//先创建一个semaphore dispatch_semaphore_t semaphore = dispatch_semaphore_create(1); __block NSMutableArray *modelArr = [[NSMutableArray alloc]init]; DataBaseTool *tool = [DataBaseTool sharedInstance]; [tool inDatabase:^(FMDatabase *db) { FMResultSet *set = [db executeQuery:@"select * from user_data where redid = ?",redid]; while ([set next]) { UserModel *model = [[UserModel alloc]init]; model.userid = [set stringForColumnIndex:1]; model.redid = [set stringForColumnIndex:2]; model.status = [set doubleForColumnIndex:3]; [modelArr addObject:model]; } [set close]; //发出已完成的信号 dispatch_semaphore_signal(semaphore); }]; //等待执行，不会占用资源 dispatch_semaphore_wait(semaphore, DISPATCH_TIME_FOREVER); return modeler;
2.使用dispatch_group
dispatch_group_t downloadGroup = dispatch_group_create(); //成对出现 任务开始时 dispatch_group_enter(downloadGroup); //成对出现 任务结束时 dispatch_group_leave(downloadGroup); dispatch_group_notify(downloadGroup, dispatch_get_main_queue(), ^{ });
