如何选择CPU和网络压力都比较小的时间发送数据包？

http://www.cocoachina.com/bbs/read.php?tid=117240

[[NSNotificationCenter defaultCenter] addObserver:self selector:@selector(notificationMethod) name:@"my_notification" object:nil];

NSNotification *notification = [NSNotificatioin notificationWithName:@"my_notification" object:nil];

[[NSNotificationQueue defaultQueue] enqueueNotification:notification postingStyle:NSPostWhenIdle];

在app空闲的时候，发出自定义消息my_notification, 执行自定义方法notificationMethod