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Monday, May 7, 2012

How to trace ANR

How to trace ANR problem !

What Triggers ANR?

In Android, application responsiveness is monitored by the Activity Manager and Window Manager system services. Android will display the ANR dialog for a particular application when it detects one of the following conditions:
  • No response to an input event (e.g. key press, screen touch) within 5 seconds
  • BroadcastReceiver hasn't finished executing within 10 seconds

How to investigate an ANR

An ANR happens when some long operation takes place in the "main" thread. This is the event loop thread, and if it is busy, Android cannot process any further GUI events in the application, and thus throws up an ANR dialog.
Now, in the trace you posted, the main thread seems to be doing fine, there is no problem. It is idling in the MessageQueue, waiting for another message to come in. In your case the ANR was likely a longer operation, rather than something that blocked the thread permanently, so the event thread recovered after the operation finished, and your trace went through after the ANR.
Detecting where ANRs happen is easy if it is a permanent block (deadlock acquiring some locks for instance), but harder if it's just a temporary delay. First, go over your code and look for vunerable spots and long running operations. Examples may include using sockets, locks, thread sleeps, and other blocking operations from within the event thread. You should make sure these all happen in separate threads. If nothing seems the problem, use DDMS and enable the thread view. This shows all the threads in your application similar to the trace you have. Reproduce the ANR, and refresh the main thread at the same time. That should show you precisely whats going on at the time of the ANR



淺談ANR及如何解決分析ANR 1
淺談ANR及如何解決分析ANR 2
淺談ANR及如何解決分析ANR 3

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