StrictMode disk access violation

[danh32]

With StrictMode fully enabled:

StrictMode.setThreadPolicy(new StrictMode.ThreadPolicy.Builder()
        .detectAll()
        .penaltyLog()
        .penaltyDeath()
        .build());
StrictMode.setVmPolicy(new StrictMode.VmPolicy.Builder()
        .detectAll()
        .penaltyLog()
        .penaltyDeath()
        .build());

I'm getting a crash on launch when calling LeakCanary.install(this);

StrictMode  D  StrictMode policy violation; ~duration=8 ms: android.os.StrictMode$StrictModeDiskReadViolation: policy=95 violation=2
            D      at android.os.StrictMode$AndroidBlockGuardPolicy.onReadFromDisk(StrictMode.java:1137)
            D      at libcore.io.BlockGuardOs.access(BlockGuardOs.java:67)
            D      at java.io.File.doAccess(File.java:283)
            D      at java.io.File.exists(File.java:363)
            D      at android.app.ContextImpl.createFilesDirLocked(ContextImpl.java:997)
            D      at android.app.ContextImpl.getFilesDir(ContextImpl.java:1020)
            D      at android.content.ContextWrapper.getFilesDir(ContextWrapper.java:201)
            D      at com.squareup.leakcanary.AndroidHeapDumper.<init>(AndroidHeapDumper.java:29)
            D      at com.squareup.leakcanary.LeakCanary.androidWatcher(LeakCanary.java:68)
            D      at com.squareup.leakcanary.LeakCanary.install(LeakCanary.java:58)
            D      at com.squareup.leakcanary.LeakCanary.install(LeakCanary.java:43)
            D      at com.robinhood.android.App.onCreate(App.java:56)
            D      at android.app.Instrumentation.callApplicationOnCreate(Instrumentation.java:1011)
            D      at android.app.ActivityThread.handleBindApplication(ActivityThread.java:4518)
            D      at android.app.ActivityThread.access$1500(ActivityThread.java:144)
            D      at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1339)
            D      at android.os.Handler.dispatchMessage(Handler.java:102)
            D      at android.os.Looper.loop(Looper.java:135)
            D      at android.app.ActivityThread.main(ActivityThread.java:5221)
            D      at java.lang.reflect.Method.invoke(Native Method)
            D      at java.lang.reflect.Method.invoke(Method.java:372)
            D      at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:899)
            D      at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:694)
AndroidRuntime  D  Shutting down VM

Calling LeakCanary.install() on a background thread fixes the issue, just thought it may be worth addressing in the lib (or in the readme) since others may also have StrictMode fully enabled for debug builds.

[pyricau]

That's really interesting. I thought of Context.getFilesDir() as a no-op, didn't think it's do some actual file reading.

We can work around that, delay the call to Context.getFilesDir() by keeping a ref to the application context and doing it at heap dump time (which happens in a background thread)

[pyricau]

There's more to it than just that, we'll need to update http://github.com/square/haha as well.

[pyricau]

As we found in #61, LeakCanaryInternals#setEnabled should be in background.

[Jacksgong]

Well done!