问题
As we know, for VoIP app, we can use Pushkit to active the app. However, It gives us only max to 30s to execute our code. After the execution time, the app is suspended. I found none method is called before it's suspend, thus, I can not do something to clear my resources. Who can help me?
来源：https://stackoverflow.com/questions/44279376/when-pushkit-wake-up-app-how-can-i-know-the-execution-time-is-finished