How come it is possible to “interact” with my app's process in DDMS even after I “exit” my app?

Question

Now, I am aware that there is no such thing as "exiting" an app in Android. By this I mean that the process corresponding to an app is kept in memory even after all the activities in that app are destroyed. (For sake of simplicity, let's keep services and such out of the picture). The process is only killed when the system decides to do so in order to reclaim memory.

However, once all my activities have been destroyed, I would assume that the process corresponding to my app is no longer "active". By this I mean that since my app is not doing any work, I assume the process no longer performs allocations. Is this assumption correct?

I used the simple default HelloWorld example that Eclipse ADT gives me via the New Android Project Wizard and saw that this is not the case. Even after I close the app, I can still track allocations in DDMS. Can anyone explain the reason for this?

Answer 1

Allocation tracker has hints for you: columns Thread Id and Allocated in. Watch these, and you'll learn which object and method did the allocation.

My inactive app shows allocations in DdmServer, which indicates that memory is used for DDMS service to work.

If you get other kind of allocations, check if your app has some outstanding threads, or other tasks that may be still running in background. If this is the case, make sure to do cleanup in Activity.onDestroy.

Answer 2

There is code running within the process because DDMS is attached to it. That code is the "remote" part of the remote debugging facility. Since there is code running there, that code will allocate memory and you will see those allocations.

If the debugger wasn't attached to the process, the OS could destroy the process if it wanted or needed to. However, because the debugger is attached, the process won't go away while you are watching it.

This is an example of the Observer effect, where you get unexpected results just because you are watching ;-)