fix: occasional deadlock configuring AVCaptureSession - WPB-23237

[samwyndham]

WPB-23237 [iOS] Replicated Once - Screen freeze and Crash observed on camera permission

Issue

Sometimes when the camera button is tapped and the preview loads we get a deadlock. I've managed to reproduce this a few times by showing and hiding the camera input repeatably but it can take time to happen. @findms originally found the issue after giving phone permissions.

Looking at the crash report in the jira ticket we see that we have called beginConfiguration on the AVCaptureSession from two threads (main + background) and that there is a deadlock before any call to commitConfiguration. Debugging I found that the main thread call happens internally when instantiating AVCaptureVideoPreviewLayer.

My fix is to first instantiate AVCaptureVideoPreviewLayer before doing our own background thread configuration of AVCaptureSession. I have observed this leads to the AVCaptureVideoPreviewLayer completing it's configuration of the session before we do it.

Testing

1. Navigate to a conversation
2. Repeatably tap the camera button so the camera input shows and hides
3. Continue for a few minutes
4. The UI should not freeze.

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Checklist

• Title contains a reference JIRA issue number like [WPB-XXX].
• Description is filled and free of optional paragraphs.
• Adds/updates automated tests.

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UI accessibility checklist

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• Make sure you use the API for UI elements that support large fonts.
• All colors are taken from WireDesign.ColorTheme or constructed using WireDesign.BaseColorPalette.
• New UI elements have Accessibility strings for VoiceOver.

[Copilot]

Pull request overview

This PR fixes an occasional deadlock issue (WPB-23237) that occurs when repeatedly showing and hiding the camera input by reordering the initialization sequence in CameraController. The deadlock was caused by concurrent configuration of the AVCaptureSession from multiple threads.

Changes:

• Moved the setupSession() call to occur after previewLayer initialization to prevent concurrent session configuration
• Added detailed inline documentation explaining the threading implications and rationale for the ordering

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[github-actions]

Test Results

1 867 tests   1 840 ✅  2m 4s ⏱️
  301 suites     27 💤
    1 files        0 ❌

Results for commit 6b6699b.

♻️ This comment has been updated with latest results.

Summary: workflow run #21716416093
Allure report (download zip): html-report-27579-fix_crash-starting-camera-preview-WPB-23237

[netbe]

LGTM;)