Deadlock with android_content_provider

[puff]

Documented behaviour

Loading artwork through an Android ContentProvider with the android_content_provider package.

Actual behaviour

Sometimes playing a new media item with an artUri using android_content_provider can freeze the app. It seems like a race condition causing a deadlock.

It hangs on this code:

audio_service/audio_service/android/src/main/java/com/ryanheise/audioservice/AudioService.java

Lines 639 to 642 in ed856d6

	synchronized (this) {
	if (artBitmap != null)
	builder.setLargeIcon(artBitmap);
	}

What I believe is happening:

• User plays item 1.
• audio_service calls setMediaItem for item 1.
  • This blocks the background thread and AudioService class in java because it's synchronized.
  • This completes normally.
• User plays item 2.
• audio_service calls setMediaItem for item 2.
  • This again blocks the background thread and AudioService.
• During this, audio_service receives a callback from the OS for building the notification (buildNotification) for item 1.
  • This blocks the main thread for audio_service as it has to wait for the setMediaItem call to complete.
• setMediaItem never completes because the android_content_provider hangs while waiting for a response from our content provider.
  • I think that audio_service is blocking the flutter thread while waiting for a response from setMediaItem, causing a deadlock where android_content_provider can't send back a response to the java method.

Here's an export of the threads in the hanged state: threads_report.txt

Removing synchronized from the code above fixes the issue, but I'm not sure of the consequences of doing this.
Because of this, I think the issue lies within audio_service, but please let me know what you think so I can try and get this fixed!

Minimal reproduction project

https://github.com/puff/audio_service/tree/deadlock_content_provider

Reproduction steps

1. Click play
2. Spam next button - you may have to click fast to trigger the bug

Output of flutter doctor

[√] Flutter (Channel stable, 3.16.4, on Microsoft Windows [Version 10.0.19045.3803], locale en-US)
[√] Windows Version (Installed version of Windows is version 10 or higher)
[!] Android toolchain - develop for Android devices (Android SDK version 34.0.0)
    X cmdline-tools component is missing
      Run `path/to/sdkmanager --install "cmdline-tools;latest"`
      See https://developer.android.com/studio/command-line for more details.
    X Android license status unknown.
      Run `flutter doctor --android-licenses` to accept the SDK licenses.
      See https://flutter.dev/docs/get-started/install/windows#android-setup for more details.
[X] Chrome - develop for the web (Cannot find Chrome executable at .\Google\Chrome\Application\chrome.exe)
    ! Cannot find Chrome. Try setting CHROME_EXECUTABLE to a Chrome executable.
[√] Visual Studio - develop Windows apps (Visual Studio Community 2022 17.8.3)
[!] Android Studio (not installed)
[√] IntelliJ IDEA Ultimate Edition (version 2023.3)
[√] Connected device (3 available)
[√] Network resources

! Doctor found issues in 3 categories.

Devices exhibiting the bug

Pixel 8 - Android 14

[Chaphasilor]

Hey @ryanheise, would you mind taking a look? If the solution really is as simple as removing the synchronized, that would allow us to finish up Android Auto support for the next release :)
I can also reproduce this bug (Zenfone 10, tested with Head Unit and actual car).

If you need any additional info, please let us know!

[puff]

Hi, I just wanted to note that we were able to work around the issue by implementing our content provider in Kotlin/Java instead of Flutter. However, I want to leave this issue open because eventually it may become essential to access data from our Flutter app in our content provider, and this issue prevents that.