ConcurrentModificationException in MetaDataStore.keysDataToJson for Crashlytics

Environment

• Android Studio version: Arctic Fox | 2020.3.1 Beta 5
• Firebase Component: Crashlytics
• Component version: 18.1.0

Problem

Normal usage of Crashlytics v18.1.0 leads to error in logcat:

E/FirebaseCrashlytics: Error serializing key/value metadata.
    java.util.ConcurrentModificationException
        at java.util.HashMap$HashIterator.nextNode(HashMap.java:1441)
        at java.util.HashMap$EntryIterator.next(HashMap.java:1475)
        at java.util.HashMap$EntryIterator.next(HashMap.java:1473)
        at java.util.Collections$UnmodifiableMap$UnmodifiableEntrySet$1.next(Collections.java:1708)
        at java.util.Collections$UnmodifiableMap$UnmodifiableEntrySet$1.next(Collections.java:1701)
        at org.json.JSONObject.<init>(JSONObject.java:138)
        at com.google.firebase.crashlytics.internal.common.MetaDataStore.keysDataToJson(MetaDataStore.java:157)
        at com.google.firebase.crashlytics.internal.common.MetaDataStore.writeKeyData(MetaDataStore.java:91)
        at com.google.firebase.crashlytics.internal.common.CrashlyticsController$8.call(CrashlyticsController.java:484)
        at com.google.firebase.crashlytics.internal.common.CrashlyticsController$8.call(CrashlyticsController.java:480)
        at com.google.firebase.crashlytics.internal.common.CrashlyticsBackgroundWorker$3.then(CrashlyticsBackgroundWorker.java:105)
        at com.google.android.gms.tasks.zzc.run(com.google.android.gms:play-services-tasks@@17.2.1:3)
        at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1167)
        at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:641)
        at com.google.firebase.crashlytics.internal.common.ExecutorUtils$1$1.onRun(ExecutorUtils.java:64)
        at com.google.firebase.crashlytics.internal.common.BackgroundPriorityRunnable.run(BackgroundPriorityRunnable.java:27)
        at java.lang.Thread.run(Thread.java:920)

Steps to reproduce:

Issue happens on application start. FirebaseCrashlytics#setUserId and FirebaseCrashlytics#log methods used from application code.

[mrichards]

Hi folks, I’m able to reproduce the bug internally and we’ll have a fix in an upcoming release. Note this does NOT cause the app to crash, but it could result in inconsistent / unexpected data when using Crashlytics’ custom key/data feature. (If you are seeing app crashes due to this, please report them here!)

While it appears that there’s a long-time bug that could result in a ConcurrentModificationException under certain circumstance (both for Unity and non-Unity apps), there was a change in the Firebase Unity 7.2.0 release that makes it considerably more likely to occur for Unity apps, especially near app launch.

(@ivangonzalez88 your repro example won’t compile against the latest release of the SDK because of recent, soon-to-be-shipped source changes. But the general principal to reproduce the bug is the same.)

[mrichards]

Hi folks, this issue is fixed as of v18.2.1!