ApplicationNotResponding sun.misc.Unsafe in park

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! Doctor found issues in 2 categories.

Version

9.12.0

Steps to Reproduce

1. take app to background
2. bring it up to foreground after some time

I see this error in the sentry itself. It has already been presumably fixed in version 7, yet I am using version 9 and it's still happening. I have got 10 events in last 30 days, which is quite a lot, considering my small user base of 14 people.

Expected Result

Works

Actual Result

io.sentry.android.core.ApplicationNotResponding: Background ANR
    at jdk.internal.misc.Unsafe.park
    at java.util.concurrent.locks.LockSupport.park(LockSupport.java:221)
    at java.util.concurrent.locks.AbstractQueuedSynchronizer.acquire(AbstractQueuedSynchronizer.java:754)
    at java.util.concurrent.locks.AbstractQueuedSynchronizer.acquire(AbstractQueuedSynchronizer.java:990)
    at java.util.concurrent.locks.ReentrantLock$Sync.lock(ReentrantLock.java:153)
    at java.util.concurrent.locks.ReentrantLock.lock(ReentrantLock.java:322)
    at io.sentry.util.AutoClosableReentrantLock.acquire(r8-map-id-4bd4561c6bc95b6e9eaa50ad6a5155dc278353ee29bbb24ceb2796fa31b59f1e:1)
    at io.sentry.android.replay.ReplayIntegration.start(r8-map-id-4bd4561c6bc95b6e9eaa50ad6a5155dc278353ee29bbb24ceb2796fa31b59f1e:3)
    at io.sentry.android.core.LifecycleWatcher.startSession(r8-map-id-4bd4561c6bc95b6e9eaa50ad6a5155dc278353ee29bbb24ceb2796fa31b59f1e:59)
    at io.sentry.android.core.LifecycleWatcher.onForeground(r8-map-id-4bd4561c6bc95b6e9eaa50ad6a5155dc278353ee29bbb24ceb2796fa31b59f1e:1)
    at io.sentry.android.core.AppState$LifecycleObserver.onStart(r8-map-id-4bd4561c6bc95b6e9eaa50ad6a5155dc278353ee29bbb24ceb2796fa31b59f1e:25)
    at androidx.lifecycle.e.b(r8-map-id-4bd4561c6bc95b6e9eaa50ad6a5155dc278353ee29bbb24ceb2796fa31b59f1e:75)
    at androidx.lifecycle.s.a(r8-map-id-4bd4561c6bc95b6e9eaa50ad6a5155dc278353ee29bbb24ceb2796fa31b59f1e:25)
    at androidx.lifecycle.t.f(r8-map-id-4bd4561c6bc95b6e9eaa50ad6a5155dc278353ee29bbb24ceb2796fa31b59f1e:361)
    at androidx.lifecycle.t.e(r8-map-id-4bd4561c6bc95b6e9eaa50ad6a5155dc278353ee29bbb24ceb2796fa31b59f1e:91)
    at androidx.lifecycle.E$a.onActivityPostStarted(r8-map-id-4bd4561c6bc95b6e9eaa50ad6a5155dc278353ee29bbb24ceb2796fa31b59f1e:24)
    at android.app.Activity.dispatchActivityPostStarted(Activity.java:1714)
    at android.app.Activity.performStart(Activity.java:9474)
    at android.app.ActivityThread.handleStartActivity(ActivityThread.java:4728)
    at android.app.servertransaction.TransactionExecutor.performLifecycleSequence(TransactionExecutor.java:217)
    at android.app.servertransaction.TransactionExecutor.cycleToPath(TransactionExecutor.java:197)
    at android.app.servertransaction.TransactionExecutor.executeLifecycleItem(TransactionExecutor.java:169)
    at android.app.servertransaction.TransactionExecutor.executeTransactionItems(TransactionExecutor.java:104)
    at android.app.servertransaction.TransactionExecutor.execute(TransactionExecutor.java:83)
    at android.app.ActivityThread$H.handleMessage(ActivityThread.java:3085)
    at android.os.Handler.dispatchMessage(Handler.java:114)
    at android.os.Looper.loopOnce(Looper.java:267)
    at android.os.Looper.loop(Looper.java:360)
    at android.app.ActivityThread.main(ActivityThread.java:10054)
    at java.lang.reflect.Method.invoke
    at com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run(RuntimeInit.java:616)
    at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:1115)

Thread: main
    at jdk.internal.misc.Unsafe.park
    at java.util.concurrent.locks.LockSupport.park(LockSupport.java:221)
    at java.util.concurrent.locks.AbstractQueuedSynchronizer.acquire(AbstractQueuedSynchronizer.java:754)
    at java.util.concurrent.locks.AbstractQueuedSynchronizer.acquire(AbstractQueuedSynchronizer.java:990)
    at java.util.concurrent.locks.ReentrantLock$Sync.lock(ReentrantLock.java:153)
    at java.util.concurrent.locks.ReentrantLock.lock(ReentrantLock.java:322)
    at io.sentry.util.AutoClosableReentrantLock.acquire(r8-map-id-4bd4561c6bc95b6e9eaa50ad6a5155dc278353ee29bbb24ceb2796fa31b59f1e:1)
    at io.sentry.android.replay.ReplayIntegration.start(r8-map-id-4bd4561c6bc95b6e9eaa50ad6a5155dc278353ee29bbb24ceb2796fa31b59f1e:3)
    at io.sentry.android.core.LifecycleWatcher.startSession(r8-map-id-4bd4561c6bc95b6e9eaa50ad6a5155dc278353ee29bbb24ceb2796fa31b59f1e:59)
    at io.sentry.android.core.LifecycleWatcher.onForeground(r8-map-id-4bd4561c6bc95b6e9eaa50ad6a5155dc278353ee29bbb24ceb2796fa31b59f1e:1)
    at io.sentry.android.core.AppState$LifecycleObserver.onStart(r8-map-id-4bd4561c6bc95b6e9eaa50ad6a5155dc278353ee29bbb24ceb2796fa31b59f1e:25)
    at androidx.lifecycle.e.b(r8-map-id-4bd4561c6bc95b6e9eaa50ad6a5155dc278353ee29bbb24ceb2796fa31b59f1e:75)
    at androidx.lifecycle.s.a(r8-map-id-4bd4561c6bc95b6e9eaa50ad6a5155dc278353ee29bbb24ceb2796fa31b59f1e:25)
    at androidx.lifecycle.t.f(r8-map-id-4bd4561c6bc95b6e9eaa50ad6a5155dc278353ee29bbb24ceb2796fa31b59f1e:361)
    at androidx.lifecycle.t.e(r8-map-id-4bd4561c6bc95b6e9eaa50ad6a5155dc278353ee29bbb24ceb2796fa31b59f1e:91)
    at androidx.lifecycle.E$a.onActivityPostStarted(r8-map-id-4bd4561c6bc95b6e9eaa50ad6a5155dc278353ee29bbb24ceb2796fa31b59f1e:24)
    at android.app.Activity.dispatchActivityPostStarted(Activity.java:1714)
    at android.app.Activity.performStart(Activity.java:9474)
    at android.app.ActivityThread.handleStartActivity(ActivityThread.java:4728)
    at android.app.servertransaction.TransactionExecutor.performLifecycleSequence(TransactionExecutor.java:217)
    at android.app.servertransaction.TransactionExecutor.cycleToPath(TransactionExecutor.java:197)
    at android.app.servertransaction.TransactionExecutor.executeLifecycleItem(TransactionExecutor.java:169)
    at android.app.servertransaction.TransactionExecutor.executeTransactionItems(TransactionExecutor.java:104)
    at android.app.servertransaction.TransactionExecutor.execute(TransactionExecutor.java:83)
    at android.app.ActivityThread$H.handleMessage(ActivityThread.java:3085)
    at android.os.Handler.dispatchMessage(Handler.java:114)
    at android.os.Looper.loopOnce(Looper.java:267)
    at android.os.Looper.loop(Looper.java:360)
    at android.app.ActivityThread.main(ActivityThread.java:10054)
    at java.lang.reflect.Method.invoke
    at com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run(RuntimeInit.java:616)
    at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:1115)

Are you willing to submit a PR?

No

[linear-code]

DART-323

[denrase]

Thank you for the report, will look into this.

[denrase]

Judging by the stack trace, this is most likely an issue in sentry-java, maybe @romtsn can give us more context if this is a knwon issue? 👀

[romtsn]

@denrase nope, not really a known issue. I guess it could happen when a replay is being finalized (via Replay/SentrySDK.close()) at the same time on a background thread or something (and hence holding the replay lifecycle lock and preventing replay from being started). Is it something the flutter sdk potentially does by default?

[buenaflor]

@romtsn we are processing the screenshot and calling onScreenshotRecorded from a separate thread: https://github.com/getsentry/sentry-dart/blob/main/packages/flutter/lib/src/native/java/android_replay_recorder.dart#L141

I think this might be happening:

1. App in foreground — replay runs, Dart isolate captures screenshots
2. App goes to background — native ReplayIntegration calls recorder.stop(). The native side assumes the recorder stopped, but the Dart scheduler is still running and the Dart worker isolate is still alive because the actual stop has to travel through multiple async hops: native → main handler post → JNI callback → Flutter engine → Dart isolate stop.
3. Dart scheduler captures another screenshot → sends to worker isolate → worker calls onScreenshotRecorded() via JNI → acquires lock
4. App comes to foreground — ReplayIntegration.start() called on main thread → tries to acquire the same lock → blocked → ANR

maybe what can help is:

// SentryFlutterReplayRecorder.kt

private val isRunning = AtomicBoolean(false)

fun isRecording(): Boolean = isRunning.get()

override fun start() {
    isRunning.set(true)
    Handler(Looper.getMainLooper()).post { ... }
}

override fun stop() {
    isRunning.set(false)  // ← immediate, no Handler.post
    Handler(Looper.getMainLooper()).post { callbacks.replayStopped() }
}

// In Flutter:
if (_nativeReplay.isRecording()) {
    _nativeReplay.onScreenshotRecorded(_bitmap!);
}

It's not a perfect fix but I think it should serve for the large majority of use cases

[romtsn]

@buenaflor sounds plausible! I think there's also a case on the Android side where we potentially run something heavy on the main thread in stop() -- probably should look into it more and fix it too

[buenaflor]

okay nvm, I thought onScreenshotRecorded holds the lock

so the root cause might be something else, perhaps the cause is mainly the heavy work in stop() as you said