[Crashlytics] Fix deadlock in user logging on reentrant queue access. (#16163)

[JesusRojass]

Discussion

This PR resolves the deadlock in the Crashlytics serial logging queue. When a thread already executing on _firclsLoggingQueue makes a call to log or write keys and values, the synchronous dispatch blocks the thread and deadlocks the serial queue.

By introducing a queue-specific key with dispatch_queue_set_specific, we can check the executing context using dispatch_get_specific. If the current thread is already running on the logging queue, the block executes directly to preserve order without deadlocking.

Fixes #16163

Testing

The change has been reviewed locally and formatted with scripts/style.sh. The Crashlytics unit test suite will be run in Xcode prior to merge.

API Changes

This change is strictly internal. There are no public API modifications.

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[JesusRojass]

/gemini review

[gemini-code-assist]

Code Review

This pull request introduces a utility function FIRCLSExecuteOnLoggingQueue to prevent potential deadlocks by checking if the current execution is already on the logging queue before performing a synchronous dispatch. The reviewer suggested adding defensive null checks for the block and the queue within this new function to improve robustness and prevent crashes in critical paths.

[JesusRojass]

/gemini review

[gemini-code-assist]

Code Review

This pull request introduces a helper function, FIRCLSExecuteOnLoggingQueue, to manage thread-safe execution on the logging queue, replacing direct dispatch_sync calls to prevent potential deadlocks. The implementation correctly sets queue-specific data to track the logging queue. A review comment suggests adding a null check for _firclsLoggingQueue before setting queue-specific data to enhance robustness.

[JesusRojass]

/gemini review

[gemini-code-assist]

Code Review

This pull request introduces a new helper function, FIRCLSExecuteOnLoggingQueue, designed to prevent deadlocks by checking for reentrancy on the logging queue before performing a synchronous dispatch. The changes include setting queue-specific data during initialization and updating logging calls to use this new utility. A review comment identifies a potential issue where blocks are silently dropped if the logging queue fails to initialize, suggesting a fallback mechanism or explicit handling for that scenario.

[JesusRojass]

/gemini review

[gemini-code-assist]

Code Review

This pull request introduces the FIRCLSExecuteOnLoggingQueue utility to safely execute blocks on the logging queue, preventing potential deadlocks by checking if the current execution context is already on that queue. The changes include initializing the logging queue with a specific key and updating FIRCLSUserLogging.m to utilize this new helper function. Review feedback suggests reordering the logic within FIRCLSExecuteOnLoggingQueue to check for the queue's existence before its specific context to improve readability and clarify the intent of the safety fallback.

[JesusRojass]

/gemini review

[gemini-code-assist]

Code Review

This pull request introduces a mechanism to prevent deadlocks on the Crashlytics logging queue by implementing a reentrancy check. It adds a helper function, FIRCLSExecuteOnLoggingQueue, which uses dispatch_get_specific to determine if a block can be executed immediately or requires a synchronous dispatch. Feedback suggests adding diagnostic logging when the logging queue is null to prevent masking potential initialization issues.