com.google.protobuf.AbstractProtobufList.ensureIsMutable (AbstractProtobufList.java:161)

### [REQUIRED] Step 2: Describe your environment

- Android Studio version: **Android Studio Quail 2 | 2026.1.2**
- Firebase Component: **Firebase performance**
- Component version: **Firebase BOM: 34.14.0**

### [REQUIRED] Step 3: Describe the problem

#### Steps to reproduce:

Stack trace from firebase Crashlytics:

- Crash: UnsupportedOperationException at AbstractProtobufList.ensureIsMutable via NetworkRequestMetricBuilder.build() → NetworkRequestMetric$Builder.addAllPerfSessions
- Trigger: InstrHttpsURLConnection.disconnect() called from a ConnectivityManager.NetworkCallback.onLost on ConnectivityThread (Braze SDK disconnecting its in-flight request on network loss), racing the request thread's own build() — i.e., NetworkRequestMetricBuilder is not thread-safe and build() runs twice
- Repro context: app in background, device loses connectivity mid-request; observed on Android 13–16, Crashlytics SDK 20.0.6

```
Fatal Exception: java.lang.UnsupportedOperationException:
at com.google.protobuf.AbstractProtobufList.ensureIsMutable(AbstractProtobufList.java:161)
at com.google.protobuf.ProtobufArrayList.add(ProtobufArrayList.java:52)
at com.google.protobuf.AbstractMessageLite$Builder.addAllCheckingNulls(AbstractMessageLite.java:361)
at com.google.protobuf.AbstractMessageLite$Builder.addAll(AbstractMessageLite.java:414)
at com.google.protobuf.AbstractMessageLite.addAll(AbstractMessageLite.java:123)
at com.google.firebase.perf.v1.NetworkRequestMetric.addAllPerfSessions(NetworkRequestMetric.java:1232)
at com.google.firebase.perf.v1.NetworkRequestMetric.access$2900(NetworkRequestMetric.java:17)
at com.google.firebase.perf.v1.NetworkRequestMetric$Builder.addAllPerfSessions(NetworkRequestMetric.java:2355)
at com.google.firebase.perf.metrics.NetworkRequestMetricBuilder.build(NetworkRequestMetricBuilder.java:318)
at com.google.firebase.perf.network.InstrURLConnectionBase.disconnect(InstrURLConnectionBase.java:80)
at com.google.firebase.perf.network.InstrHttpsURLConnection.disconnect(InstrHttpsURLConnection.java:63)
at bo.app.i7.a(SourceFile:3)
at bo.app.i7.c(SourceFile:3)
at bo.app.f7.g(SourceFile:2)
at bo.app.y6.a(SourceFile:130)
at bo.app.y6.a(SourceFile:35)
at bo.app.m8.b(SourceFile:62)
at bo.app.c5.a(SourceFile:29)
at bo.app.y4.onLost(SourceFile:8)
at android.net.ConnectivityManager$CallbackHandler.handleMessage(ConnectivityManager.java:4688)
at android.os.Handler.dispatchMessage(Handler.java:132)
at android.os.Looper.dispatchMessage(Looper.java:358)
at android.os.Looper.loopOnce(Looper.java:288)
at android.os.Looper.loop(Looper.java:392)
at android.os.HandlerThread.run(HandlerThread.java:139)

Firebase Background Thread #1:
at dalvik.system.VMStack.getThreadStackTrace(VMStack.java)
at java.lang.Thread.getStackTrace(Thread.java:2852)
at java.lang.Thread.getAllStackTraces(Thread.java:2919)
at com.google.firebase.crashlytics.internal.common.CrashlyticsReportDataCapture.populateThreadsList(CrashlyticsReportDataCapture.java:343)
at com.google.firebase.crashlytics.internal.common.CrashlyticsReportDataCapture.populateExecutionData(CrashlyticsReportDataCapture.java:314)
at com.google.firebase.crashlytics.internal.common.CrashlyticsReportDataCapture.populateEventApplicationData(CrashlyticsReportDataCapture.java:261)
at com.google.firebase.crashlytics.internal.common.CrashlyticsReportDataCapture.captureEventData(CrashlyticsReportDataCapture.java:112)
at com.google.firebase.crashlytics.internal.common.SessionReportingCoordinator.persistEvent(SessionReportingCoordinator.java:337)
at com.google.firebase.crashlytics.internal.common.SessionReportingCoordinator.persistFatalEvent(SessionReportingCoordinator.java:130)
at com.google.firebase.crashlytics.internal.common.CrashlyticsController$2.call(CrashlyticsController.java:219)
at com.google.firebase.crashlytics.internal.common.CrashlyticsController$2.call(CrashlyticsController.java:205)
at com.google.firebase.crashlytics.internal.concurrency.CrashlyticsWorker.lambda$submitTask$2(CrashlyticsWorker.java:118)
at com.google.android.gms.tasks.zze.run(zze.java:1)
at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1100)
at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:624)
at com.google.firebase.concurrent.CustomThreadFactory.lambda$newThread$0(CustomThreadFactory.java:47)
at java.lang.Thread.run(Thread.java:1572)

kotlinx.coroutines.DefaultExecutor:
at jdk.internal.misc.Unsafe.park(Unsafe.java)
at java.util.concurrent.locks.LockSupport.parkNanos(LockSupport.java:276)
at kotlinx.coroutines.DefaultExecutor.run(DefaultExecutor.kt:118)
at java.lang.Thread.run(Thread.java:1572)

ProcessStablePhenotypeFlag:
at jdk.internal.misc.Unsafe.park(Unsafe.java)
at java.util.concurrent.locks.LockSupport.park(LockSupport.java:376)
at java.util.concurrent.locks.AbstractQueuedSynchronizer$ConditionNode.block(AbstractQueuedSynchronizer.java:520)
at java.util.concurrent.ForkJoinPool.unmanagedBlock(ForkJoinPool.java:3797)
at java.util.concurrent.ForkJoinPool.managedBlock(ForkJoinPool.java:3738)
at java.util.concurrent.locks.AbstractQueuedSynchronizer$ConditionObject.await(AbstractQueuedSynchronizer.java:1752)
at java.util.concurrent.ScheduledThreadPoolExecutor$DelayedWorkQueue.take(ScheduledThreadPoolExecutor.java:1170)
at java.util.concurrent.ScheduledThreadPoolExecutor$DelayedWorkQueue.take(ScheduledThreadPoolExecutor.java:899)
at java.util.concurrent.ThreadPoolExecutor.getTask(ThreadPoolExecutor.java:1026)
at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1086)
at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:624)
at java.lang.Thread.run(Thread.java:1572)

ConscryptStatsLogWriter:
at jdk.internal.misc.Unsafe.park(Unsafe.java)
at java.util.concurrent.locks.LockSupport.park(LockSupport.java:376)
at java.util.concurrent.locks.AbstractQueuedSynchronizer$ConditionNode.block(AbstractQueuedSynchronizer.java:520)
at java.util.concurrent.ForkJoinPool.unmanagedBlock(ForkJoinPool.java:3797)
at java.util.concurrent.ForkJoinPool.managedBlock(ForkJoinPool.java:3738)
at java.util.concurrent.locks.AbstractQueuedSynchronizer$ConditionObject.await(AbstractQueuedSynchronizer.java:1752)
at java.util.concurrent.LinkedBlockingQueue.take(LinkedBlockingQueue.java:435)
at java.util.concurrent.ThreadPoolExecutor.getTask(ThreadPoolExecutor.java:1026)
at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1086)
at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:624)
at java.lang.Thread.run(Thread.java:1572)

DefaultDispatcher-worker-17:
at jdk.internal.misc.Unsafe.park(Unsafe.java)
at java.util.concurrent.locks.LockSupport.parkNanos(LockSupport.java:417)
at kotlinx.coroutines.scheduling.CoroutineScheduler$Worker.park(CoroutineScheduler.kt:833)
at kotlinx.coroutines.scheduling.CoroutineScheduler$Worker.tryPark(CoroutineScheduler.kt:781)
at kotlinx.coroutines.scheduling.CoroutineScheduler$Worker.runWorker(CoroutineScheduler.kt:751)
at kotlinx.coroutines.scheduling.CoroutineScheduler$Worker.run(CoroutineScheduler.kt:704)

Firebase-Messaging-Init:
at jdk.internal.misc.Unsafe.park(Unsafe.java)
at java.util.concurrent.locks.LockSupport.park(LockSupport.java:376)
at java.util.concurrent.locks.AbstractQueuedSynchronizer$ConditionNode.block(AbstractQueuedSynchronizer.java:520)
at java.util.concurrent.ForkJoinPool.unmanagedBlock(ForkJoinPool.java:3797)
at java.util.concurrent.ForkJoinPool.managedBlock(ForkJoinPool.java:3738)
at java.util.concurrent.locks.AbstractQueuedSynchronizer$ConditionObject.await(AbstractQueuedSynchronizer.java:1752)
at java.util.concurrent.ScheduledThreadPoolExecutor$DelayedWorkQueue.take(ScheduledThreadPoolExecutor.java:1170)
at java.util.concurrent.ScheduledThreadPoolExecutor$DelayedWorkQueue.take(ScheduledThreadPoolExecutor.java:899)
at java.util.concurrent.ThreadPoolExecutor.getTask(ThreadPoolExecutor.java:1026)
at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1086)
at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:624)
at com.google.android.gms.common.util.concurrent.zza.run(zza.java:2)
at java.lang.Thread.run(Thread.java:1572)

pool-18-thread-1:
at jdk.internal.misc.Unsafe.park(Unsafe.java)
at java.util.concurrent.locks.LockSupport.park(LockSupport.java:376)
at java.util.concurrent.locks.AbstractQueuedSynchronizer$ConditionNode.block(AbstractQueuedSynchronizer.java:520)
at java.util.concurrent.ForkJoinPool.unmanagedBlock(ForkJoinPool.java:3797)
at java.util.concurrent.ForkJoinPool.managedBlock(ForkJoinPool.java:3738)
at java.util.concurrent.locks.AbstractQueuedSynchronizer$ConditionObject.await(AbstractQueuedSynchronizer.java:1752)
at java.util.concurrent.LinkedBlockingQueue.take(LinkedBlockingQueue.java:435)
at java.util.concurrent.ThreadPoolExecutor.getTask(ThreadPoolExecutor.java:1026)
at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1086)
at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:624)
at java.lang.Thread.run(Thread.java:1572)

queue-1-2:
at jdk.internal.misc.Unsafe.park(Unsafe.java)
at java.util.concurrent.locks.LockSupport.park(LockSupport.java:376)
at java.util.concurrent.locks.AbstractQueuedSynchronizer$ConditionNode.block(AbstractQueuedSynchronizer.java:520)
at java.util.concurrent.ForkJoinPool.unmanagedBlock(ForkJoinPool.java:3797)
at java.util.concurrent.ForkJoinPool.managedBlock(ForkJoinPool.java:3738)
at java.util.concurrent.locks.AbstractQueuedSynchronizer$ConditionObject.await(AbstractQueuedSynchronizer.java:1752)
at java.util.concurrent.LinkedBlockingQueue.take(LinkedBlockingQueue.java:435)
at java.util.concurrent.ThreadPoolExecutor.getTask(ThreadPoolExecutor.java:1026)
at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1086)
at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:624)
at java.lang.Thread.run(Thread.java:1572)

pool-29-thread-1:
at jdk.internal.misc.Unsafe.park(Unsafe.java)
at java.util.concurrent.locks.LockSupport.park(LockSupport.java:376)
at java.util.concurrent.locks.AbstractQueuedSynchronizer$ConditionNode.block(AbstractQueuedSynchronizer.java:520)
at java.util.concurrent.ForkJoinPool.unmanagedBlock(ForkJoinPool.java:3797)
at java.util.concurrent.ForkJoinPool.managedBlock(ForkJoinPool.java:3738)
at java.util.concurrent.locks.AbstractQueuedSynchronizer$ConditionObject.await(AbstractQueuedSynchronizer.java:1752)
at java.util.concurrent.ScheduledThreadPoolExecutor$DelayedWorkQueue.take(ScheduledThreadPoolExecutor.java:1170)
at java.util.concurrent.ScheduledThreadPoolExecutor$DelayedWorkQueue.take(ScheduledThreadPoolExecutor.java:899)
at java.util.concurrent.ThreadPoolExecutor.getTask(ThreadPoolExecutor.java:1026)
at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1086)
at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:624)
at java.lang.Thread.run(Thread.java:1572)

RxComputationThreadPool-2:
at jdk.internal.misc.Unsafe.park(Unsafe.java)
at java.util.concurrent.locks.LockSupport.park(LockSupport.java:376)
at java.util.concurrent.locks.AbstractQueuedSynchronizer$ConditionNode.block(AbstractQueuedSynchronizer.java:520)
at java.util.concurrent.ForkJoinPool.unmanagedBlock(ForkJoinPool.java:3797)
at java.util.concurrent.ForkJoinPool.managedBlock(ForkJoinPool.java:3738)
at java.util.concurrent.locks.AbstractQueuedSynchronizer$ConditionObject.await(AbstractQueuedSynchronizer.java:1752)
at java.util.concurrent.ScheduledThreadPoolExecutor$DelayedWorkQueue.take(ScheduledThreadPoolExecutor.java:1170)
at java.util.concurrent.ScheduledThreadPoolExecutor$DelayedWorkQueue.take(ScheduledThreadPoolExecutor.java:899)
at java.util.concurrent.ThreadPoolExecutor.getTask(ThreadPoolExecutor.java:1026)
at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1086)
at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:624)
at java.lang.Thread.run(Thread.java:1572)
at okio.AsyncTimeout$Watchdog.run(AsyncTimeout.kt:5)

ConscryptStatsLogWriter:
at jdk.internal.misc.Unsafe.park(Unsafe.java)
at java.util.concurrent.locks.LockSupport.park(LockSupport.java:376)
at java.util.concurrent.locks.AbstractQueuedSynchronizer$ConditionNode.block(AbstractQueuedSynchronizer.java:520)
at java.util.concurrent.ForkJoinPool.unmanagedBlock(ForkJoinPool.java:3797)
at java.util.concurrent.ForkJoinPool.managedBlock(ForkJoinPool.java:3738)
at java.util.concurrent.locks.AbstractQueuedSynchronizer$ConditionObject.await(AbstractQueuedSynchronizer.java:1752)
at java.util.concurrent.LinkedBlockingQueue.take(LinkedBlockingQueue.java:435)
at java.util.concurrent.ThreadPoolExecutor.getTask(ThreadPoolExecutor.java:1026)
at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1086)
at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:624)
at java.lang.Thread.run(Thread.java:1572)

Firebase Scheduler Thread #0:
at jdk.internal.misc.Unsafe.park(Unsafe.java)
at java.util.concurrent.locks.LockSupport.park(LockSupport.java:376)
at java.util.concurrent.locks.AbstractQueuedSynchronizer$ConditionNode.block(AbstractQueuedSynchronizer.java:520)
at java.util.concurrent.ForkJoinPool.unmanagedBlock(ForkJoinPool.java:3797)
at java.util.concurrent.ForkJoinPool.managedBlock(ForkJoinPool.java:3738)
at java.util.concurrent.locks.AbstractQueuedSynchronizer$ConditionObject.await(AbstractQueuedSynchronizer.java:1752)
at java.util.concurrent.ScheduledThreadPoolExecutor$DelayedWorkQueue.take(ScheduledThreadPoolExecutor.java:1170)
at java.util.concurrent.ScheduledThreadPoolExecutor$DelayedWorkQueue.take(ScheduledThreadPoolExecutor.java:899)
at java.util.concurrent.ThreadPoolExecutor.getTask(ThreadPoolExecutor.java:1026)
at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1086)
at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:624)
at com.google.firebase.concurrent.CustomThreadFactory.lambda$newThread$0(CustomThreadFactory.java:47)
at java.lang.Thread.run(Thread.java:1572)

DefaultDispatcher-worker-11:
at jdk.internal.misc.Unsafe.park(Unsafe.java)
at java.util.concurrent.locks.LockSupport.parkNanos(LockSupport.java:417)
at kotlinx.coroutines.scheduling.CoroutineScheduler$Worker.park(CoroutineScheduler.kt:833)
at kotlinx.coroutines.scheduling.CoroutineScheduler$Worker.tryPark(CoroutineScheduler.kt:781)
at kotlinx.coroutines.scheduling.CoroutineScheduler$Worker.runWorker(CoroutineScheduler.kt:751)
at kotlinx.coroutines.scheduling.CoroutineScheduler$Worker.run(CoroutineScheduler.kt:704)

pool-31-thread-1:
at jdk.internal.misc.Unsafe.park(Unsafe.java)
at java.util.concurrent.locks.LockSupport.park(LockSupport.java:376)
at java.util.concurrent.locks.AbstractQueuedSynchronizer$ConditionNode.block(AbstractQueuedSynchronizer.java:520)
at java.util.concurrent.ForkJoinPool.unmanagedBlock(ForkJoinPool.java:3797)
at java.util.concurrent.ForkJoinPool.managedBlock(ForkJoinPool.java:3738)
at java.util.concurrent.locks.AbstractQueuedSynchronizer$ConditionObject.await(AbstractQueuedSynchronizer.java:1752)
at java.util.concurrent.LinkedBlockingQueue.take(LinkedBlockingQueue.java:435)
at java.util.concurrent.ThreadPoolExecutor.getTask(ThreadPoolExecutor.java:1026)
at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1086)
at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:624)
at java.lang.Thread.run(Thread.java:1572)

WM.task-4:
at jdk.internal.misc.Unsafe.park(Unsafe.java)
at java.util.concurrent.locks.LockSupport.park(LockSupport.java:376)
at java.util.concurrent.locks.AbstractQueuedSynchronizer$ConditionNode.block(AbstractQueuedSynchronizer.java:520)
at java.util.concurrent.ForkJoinPool.unmanagedBlock(ForkJoinPool.java:3797)
at java.util.concurrent.ForkJoinPool.managedBlock(ForkJoinPool.java:3738)
at java.util.concurrent.locks.AbstractQueuedSynchronizer$ConditionObject.await(AbstractQueuedSynchronizer.java:1752)
at java.util.concurrent.LinkedBlockingQueue.take(LinkedBlockingQueue.java:435)
at java.util.concurrent.ThreadPoolExecutor.getTask(ThreadPoolExecutor.java:1026)
at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1086)
at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:624)
at java.lang.Thread.run(Thread.java:1572)

FrameMetricsAggregator:
at android.os.MessageQueue.nativePollOnce(MessageQueue.java)
at android.os.MessageQueue.nextLegacy(MessageQueue.java:985)
at android.os.MessageQueue.next(MessageQueue.java:1094)
at android.os.Looper.loopOnce(Looper.java:222)
at android.os.Looper.loop(Looper.java:392)
at android.os.HandlerThread.run(HandlerThread.java:139)

Timer-0:
at java.lang.Object.wait(Object.java)
at java.lang.Object.wait(Object.java:405)
at java.lang.Object.wait(Object.java:543)
at java.util.TimerThread.mainLoop(Timer.java:562)
at java.util.TimerThread.run(Timer.java:540)

RxCachedThreadScheduler-54:
at jdk.internal.misc.Unsafe.park(Unsafe.java)
at java.util.concurrent.locks.LockSupport.park(LockSupport.java:376)
at java.util.concurrent.locks.AbstractQueuedSynchronizer$ConditionNode.block(AbstractQueuedSynchronizer.java:520)
at java.util.concurrent.ForkJoinPool.unmanagedBlock(ForkJoinPool.java:3797)
at java.util.concurrent.ForkJoinPool.managedBlock(ForkJoinPool.java:3738)
at java.util.concurrent.locks.AbstractQueuedSynchronizer$ConditionObject.await(AbstractQueuedSynchronizer.java:1752)
at java.util.concurrent.ScheduledThreadPoolExecutor$DelayedWorkQueue.take(ScheduledThreadPoolExecutor.java:1170)
at java.util.concurrent.ScheduledThreadPoolExecutor$DelayedWorkQueue.take(ScheduledThreadPoolExecutor.java:899)
at java.util.concurrent.ThreadPoolExecutor.getTask(ThreadPoolExecutor.java:1026)
at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1086)
at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:624)
at java.lang.Thread.run(Thread.java:1572)

Firebase Background Thread #2:
at jdk.internal.misc.Unsafe.park(Unsafe.java)
at java.util.concurrent.locks.LockSupport.park(LockSupport.java:376)
at java.util.concurrent.locks.AbstractQueuedSynchronizer$ConditionNode.block(AbstractQueuedSynchronizer.java:520)
at java.util.concurrent.ForkJoinPool.unmanagedBlock(ForkJoinPool.java:3797)
at java.util.concurrent.ForkJoinPool.managedBlock(ForkJoinPool.java:3738)
at java.util.concurrent.locks.AbstractQueuedSynchronizer$ConditionObject.await(AbstractQueuedSynchronizer.java:1752)
at java.util.concurrent.LinkedBlockingQueue.take(LinkedBlockingQueue.java:435)
at java.util.concurrent.ThreadPoolExecutor.getTask(ThreadPoolExecutor.java:1026)
at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1086)
at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:624)
at com.google.firebase.concurrent.CustomThreadFactory.lambda$newThread$0(CustomThreadFactory.java:47)
at java.lang.Thread.run(Thread.java:1572)

RxComputationThreadPool-5:
at jdk.internal.misc.Unsafe.park(Unsafe.java)
at java.util.concurrent.locks.LockSupport.park(LockSupport.java:376)
at java.util.concurrent.locks.AbstractQueuedSynchronizer$ConditionNode.block(AbstractQueuedSynchronizer.java:520)
at java.util.concurrent.ForkJoinPool.unmanagedBlock(ForkJoinPool.java:3797)
at java.util.concurrent.ForkJoinPool.managedBlock(ForkJoinPool.java:3738)
at java.util.concurrent.locks.AbstractQueuedSynchronizer$ConditionObject.await(AbstractQueuedSynchronizer.java:1752)
at java.util.concurrent.ScheduledThreadPoolExecutor$DelayedWorkQueue.take(ScheduledThreadPoolExecutor.java:1170)
at java.util.concurrent.ScheduledThreadPoolExecutor$DelayedWorkQueue.take(ScheduledThreadPoolExecutor.java:899)
at java.util.concurrent.ThreadPoolExecutor.getTask(ThreadPoolExecutor.java:1026)
at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1086)
at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:624)
at java.lang.Thread.run(Thread.java:1572)
at okio.AsyncTimeout$Watchdog.run(AsyncTimeout.kt:5)

RxComputationThreadPool-7:
at jdk.internal.misc.Unsafe.park(Unsafe.java)
at java.util.concurrent.locks.LockSupport.park(LockSupport.java:376)
at java.util.concurrent.locks.AbstractQueuedSynchronizer$ConditionNode.block(AbstractQueuedSynchronizer.java:520)
at java.util.concurrent.ForkJoinPool.unmanagedBlock(ForkJoinPool.java:3797)
at java.util.concurrent.ForkJoinPool.managedBlock(ForkJoinPool.java:3738)
at java.util.concurrent.locks.AbstractQueuedSynchronizer$ConditionObject.await(AbstractQueuedSynchronizer.java:1752)
at java.util.concurrent.ScheduledThreadPoolExecutor$DelayedWorkQueue.take(ScheduledThreadPoolExecutor.java:1170)
at java.util.concurrent.ScheduledThreadPoolExecutor$DelayedWorkQueue.take(ScheduledThreadPoolExecutor.java:899)
at java.util.concurrent.ThreadPoolExecutor.getTask(ThreadPoolExecutor.java:1026)
at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1086)
at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:624)
at java.lang.Thread.run(Thread.java:1572)
at okio.AsyncTimeout$Watchdog.run(AsyncTimeout.kt:5)

DefaultDispatcher-worker-7:
at jdk.internal.misc.Unsafe.park(Unsafe.java)
at java.util.concurrent.locks.LockSupport.parkNanos(LockSupport.java:417)
at kotlinx.coroutines.scheduling.CoroutineScheduler$Worker.park(CoroutineScheduler.kt:833)
at kotlinx.coroutines.scheduling.CoroutineScheduler$Worker.tryPark(CoroutineScheduler.kt:781)
at kotlinx.coroutines.scheduling.CoroutineScheduler$Worker.runWorker(CoroutineScheduler.kt:751)
at kotlinx.coroutines.scheduling.CoroutineScheduler$Worker.run(CoroutineScheduler.kt:704)

Firebase Blocking Thread #195:
at jdk.internal.misc.Unsafe.park(Unsafe.java)
at java.util.concurrent.locks.LockSupport.parkNanos(LockSupport.java:417)
at java.util.concurrent.LinkedTransferQueue$DualNode.await(LinkedTransferQueue.java:452)
at java.util.concurrent.SynchronousQueue$Transferer.xferLifo(SynchronousQueue.java:194)
at java.util.concurrent.SynchronousQueue.xfer(SynchronousQueue.java:235)
at java.util.concurrent.SynchronousQueue.poll(SynchronousQueue.java:338)
at java.util.concurrent.ThreadPoolExecutor.getTask(ThreadPoolExecutor.java:1025)
at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1086)
at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:624)
at com.google.firebase.concurrent.CustomThreadFactory.lambda$newThread$0(CustomThreadFactory.java:47)
at java.lang.Thread.run(Thread.java:1572)

```

Seems to be the same issue reported on https://github.com/firebase/firebase-android-sdk/issues/6625

Start with NetworkRequestMetricBuilder.build() and follow the stack-trace path through InstrURLConnectionBase.disconnect() and InstrHttpsURLConnection.disconnect(). Investigate the concurrent build calls described in the reproduction, then verify that losing connectivity during an in-flight request no longer produces UnsupportedOperationException at AbstractProtobufList.ensureIsMutable.

Written by the indexing model from the issue text.