NPE in ExtractorMediaSource, reproduced by quickly prepare and release the MediaSource

[eneim]

In short, here is my stacktrace:

Fatal Exception: java.lang.NullPointerException: Attempt to invoke interface method 'void com.google.android.exoplayer2.source.MediaSource$Listener.onSourceInfoRefreshed(com.google.android.exoplayer2.Timeline, java.lang.Object)' on a null object reference
       at com.google.android.exoplayer2.source.ExtractorMediaSource.onSourceInfoRefreshed(ExtractorMediaSource.java:179)
       at com.google.android.exoplayer2.source.ExtractorMediaPeriod.maybeFinishPrepare(ExtractorMediaPeriod.java:408)
       at com.google.android.exoplayer2.source.ExtractorMediaPeriod.access$000(ExtractorMediaPeriod.java:49)
       at com.google.android.exoplayer2.source.ExtractorMediaPeriod$1.run(ExtractorMediaPeriod.java:120)
       at android.os.Handler.handleCallback(Handler.java:751)
       at android.os.Handler.dispatchMessage(Handler.java:95)
       at android.os.Looper.loop(Looper.java:154)
       at android.os.HandlerThread.run(HandlerThread.java:61)
       at com.google.android.exoplayer2.util.PriorityHandlerThread.run(PriorityHandlerThread.java:40)

It happens when I have a list or video (RecyclerView), and scroll quickly through them (when a ViewHolder is attached to Window, it will prepare the Video with "playWhenReady = false").

Source code is from my library, so have no idea if it is OK to show it here. But let me know.

[ojw28]

If it's possible to provide an easy way to reproduce this as source (e.g. a patch for the demo app, or a link to some other open source demo app that reproduces the issue) that would be great.

The only way I can see this happening is if the ExtractorMediaSource has been released whilst one of its child ExtractorMediaPeriods has not, and I can't see an obvious way that can happen.

[mopsalarm]

I have the same issue in my app. Sadly, i dont know how to reproduce it, as it only happens on my users systems, never on mine. I am calling prepareSource() and stop() maybe multiple times on an exo player instance inside of a ViewPager.

[ojw28]

Which versions of ExoPlayer are you seeing this with? Unless you've shipped your app extremely recently I'd expect you to be seeing a different stack trace (even if only by the line numbers).

[mopsalarm]

2.0.0 and 2.0.2. I skipped the 2.0.1 release. I am putting daily/every-second-day builds out there.
The NPE occurres in Line 179 in ExtractorMediaSource.

[ojw28]

Could you point me to your app in Play Store? I'd be interested in trying to reproduce. Thanks!

[mopsalarm]

Sadly, it is not in the play store - but you can find the repository here: https://github.com/mopsalarm/Pr0/tree/1.111.4
In the current master version, i use a exo player version with an if (sourceListener != null) added.

The ExoPlayer is wrapped here https://github.com/mopsalarm/Pr0/blob/1.111.4/app/src/main/java/com/pr0gramm/app/ui/views/viewer/video/ExoVideoPlayer.java
The start() and stop() Methods might be called multiple times during the Lifetime of this class.

[ojw28]

@mopsalarm - I checked out master and switched the dependency back to vanilla ExoPlayer. Should that be sufficient to get the app into a state where it might reproduce the issue (albeit that reproducing might be difficult). Do you know in which fragment the issue occurs, and what browsing steps I'd need to take to get to that fragment in the app? If not, that might be something you could usefully log in future releases, if you fancy helping to chase this down.

[ojw28]

Actually, it reproduces relatively easily (e.g. within 5 minutes or so) if you unleash the monkey on your app, like:

adb shell monkey -p com.pr0gramm.app -v 500

(repeat until crash occurs).

[eneim]

@ojw28 I notice that in ExtractorMediaSource, It passes itself to a new ExtractorMediaPeriod in createPeriod but it has never been released in releasePeriod (see ExtractorMediaPeriod#release()), which I guess the cause for this issue. It can be seen that if a call to ExoPlayer#stop() is called before the source is prepared, it will throw an NPE.

[mopsalarm]

nice 👍