Crash in StorageObservableTask / StorageDownloadTask.enqueueImplementation — recurring since at least SDK 10.11.0 (see #11875), still present in 12.16.0

[Lazynius1]

Description

We're seeing crashes deep inside FirebaseStorage's task/observer lifecycle:

#9  StorageObservableTask.removeAllObservers() (StorageObservableTask.swift:113)
#10 StorageDownloadTask.enqueueImplementation(resumeWith:) (StorageDownloadTask.swift:179)
#11 closure #1 in StorageDownloadTask.enqueue() (StorageDownloadTask.swift:42)

This looks like the same crash family reported in #11875 ("Crash in StorageObservableTask"), which was closed due to inactivity/no-recent-activity rather than being fixed. That report was on SDK 10.11.0 (Xcode 14.3) with a crash in StorageObservableTask.fire(handlers:snapshot:) called from StorageDownloadTask.enqueueImplementation. We're now seeing a crash in the same file/class (removeAllObservers(), also called from enqueueImplementation) on SDK 12.16.0 — so this appears to be a long-standing, unresolved issue in the observer/task lifecycle of StorageObservableTask, not something fixed between those versions.

Our usage of Storage is the standard documented pattern (task.observe(.progress), .observe(.success), .observe(.failure)) — we don't call removeAllObservers() ourselves. The crash happens inside the SDK's own task enqueue/observer teardown path, which suggests a threading race: removeAllObservers() mutating the observer collection while a task is concurrently enqueuing/firing handlers.

It's happened without any obvious trigger on our end — once with no user interaction in progress, and once while the user was simply adjusting an unrelated UI control (a drawing tool size slider) with no Storage activity intentionally initiated at that moment, suggesting a background download/upload task's async callback raced with a teardown.

Reproducing the issue

No consistent repro steps yet — it appears intermittently during normal app usage while Storage downloads/uploads are happening in the background (chat media, story assets), not tied to a specific user action. Will update if we find a reliable repro.

Firebase SDK Version

12.16.0

Xcode Version

27 beta 3

Installation Method

Swift Package Manager

Firebase Product(s)

Storage

Targeted Platforms

iOS

Relevant Log Output

#9  0x0000000109d2fa68 in StorageObservableTask.removeAllObservers() at FirebaseStorage/Sources/StorageObservableTask.swift:113
#10 0x0000000109d1e7ec in StorageDownloadTask.enqueueImplementation(resumeWith:) at FirebaseStorage/Sources/StorageDownloadTask.swift:179
#11 0x0000000109d1a35c in closure #1 in StorageDownloadTask.enqueue() at FirebaseStorage/Sources/StorageDownloadTask.swift:42

Will enable -FIRDebugEnabled and update with fuller logs if it recurs.

If using Swift Package Manager, the project's Package.resolved

No response

If using CocoaPods, the project's Podfile.lock

No response

[paulb777]

Thanks for the report. The upcoming 12.17.0, due out the week of July 28th, has includes several thread safety fixes, that may fix this issue. See #16359 for more details.

[Lazynius1]

Thanks for the quick response, @paulb777! Looked at #16359 and it looks very promising — the changes to StorageObservableTask (synchronized handlerDictionaries access via stateLock, atomic observe(_:handler:)) line up directly with where our crash was happening (removeAllObservers() called from StorageDownloadTask.enqueueImplementation).

We'll upgrade to 12.17.0 once it's out and report back here whether it resolves it. Appreciate the pointer!

[paulb777]

12.17.0 released this week.

[google-oss-bot]

Hey @Lazynius1. We need more information to resolve this issue but there hasn't been an update in 5 weekdays. I'm marking the issue as stale and if there are no new updates in the next 5 days I will close it automatically.

If you have more information that will help us get to the bottom of this, just add a comment!