IssueTracker

How to reproduce？

1. make FrameworksMockingServicesTests
2. adb install -r -t FrameworksMockingServicesTests.apk
3. adb shell am instrument -e class com.android.server.am.CachedAppOptimizerTest -w com.android.frameworks.mockingservicestests/androidx.test.runner.AndroidJUnitRunner

com.android.server.am.CachedAppOptimizerTest:. Process crashed while executing fullCompactionDeltaRssThrottleKb_listensToDeviceConfigChangesBadValues(com.android.server.am.CachedAppOptimizerTest): java.lang.NullPointerException: Attempt to invoke virtual method 'java.util.Set java.util.HashMap.keySet()' on a null object reference at android.provider.DeviceConfig$Properties.getKeyset(DeviceConfig.java:1517) at com.android.server.am.CachedAppOptimizer$1.onPropertiesChanged(CachedAppOptimizer.java:287) at com.android.modules.utils.testing.TestableDeviceConfig.lambda$invokeListeners$13(TestableDeviceConfig.java:181) at com.android.modules.utils.testing.TestableDeviceConfig$$ExternalSyntheticLambda12.run(Unknown Source:4) at android.os.Handler.handleCallback(Handler.java:958) at android.os.Handler.dispatchMessage(Handler.java:99) at android.os.Looper.loopOnce(Looper.java:222) at android.os.Looper.loop(Looper.java:314) at android.app.ActivityThread.main(ActivityThread.java:8561) at java.lang.reflect.Method.invoke(Native Method) at com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run(RuntimeInit.java:561) at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:959) INSTRUMENTATION_RESULT: shortMsg=Process crashed. INSTRUMENTATION_CODE: 0

How to Fix

From analysis, I think this is a corner case of TestableDeviceConfig. We should create a spy of the real Properties object instead of mocking it. As the testing thread is always not the same thread as invoking listeners thread, if we tear down tesing and finish mocking at a very delicate time, the invoking listener thread could cause NPE when calling Properties.getKeyset.

https://android-review.googlesource.com/c/platform/frameworks/libs/modules-utils/+/2612889

     private Properties getProperties(String namespace, Map<String, String> keyValues) {
-        Properties properties = Mockito.mock(Properties.class);
+        Properties properties = spy(new Properties(namespace, keyValues));
         when(properties.getNamespace()).thenReturn(namespace);
         when(properties.getKeyset()).thenReturn(keyValues.keySet());