不抱歉。您可以在Google官方文档中阅读标准的GCM推送通知（ https://developers.google .com / cloud-messaging / concept-options ）是一项尽力服务。我引用：
$ b

换句话说，GCM将保证尽最大努力为那些必须现在或从不提供的消息。

如果您正在寻找可靠的推送消息传送API，您可以尝试 Catapush 。我们使用XMPP协议（如Whatsapp一样）为设备添加自己的实时后台连接，从而能够在大多数紧急情况下更快速地传递消息。另外，我们还会跟踪发送的每个消息（发送，传送，读取，......）的实时状态，从而使您的系统能够实时做出反应。

I wonder if it's okay to use a push-notification message rather than a service, or in other words, if it is totally reliable the push notifications delivery. I know IOS is not trustable, but I am not sure if Google is guaranteeing the delivery. So, please enlighten me.

Nope sorry. The standard GCM push notifications as you can read on Google’s official documentation ( https://developers.google.com/cloud-messaging/concept-options ) are a best effort service. I quote:

In other words, GCM will guarantee best effort for messages that must be delivered "now or never."

If you are looking for reliable push messages delivery API you can give Catapush a try. We add your own real time background connection with devices using XMPP protocol (as Whatsapp does) thus having the ability to deliver messages faster and under most critical situations. In addition we track real time status of each message sent (sent, delivered, read,..) enabling your system to react in real time.