[C-API] Introduce TVMFFIHandleInitOnce

[tqchen]

In DSL settings, sometimes it is helpful to have ability to do thread-safe initialization of static handles.
This PR adds two functions to make it easy to do so without stdcpp run_once support

[gemini-code-assist]

Summary of Changes

Hello @tqchen, I'm Gemini Code Assist¹! I'm currently reviewing this pull request and will post my feedback shortly. In the meantime, here's a summary to help you and other reviewers quickly get up to speed!

This pull request introduces a robust mechanism for thread-safe, one-time initialization and deinitialization of static handles within the TVM FFI environment. This is particularly useful in DSL contexts where ensuring a resource is initialized and deinitialized exactly once, even across multiple threads, is critical, without relying on C++11 std::call_once features. The new functions, TVMFFIEnvHandleInitOnce and TVMFFIEnvHandleDeinitOnce, provide a portable and reliable solution for managing resource lifecycles in concurrent environments.

Highlights

• New API for Thread-Safe Handle Initialization: Introduced TVMFFIEnvHandleInitOnce to provide a thread-safe mechanism for initializing static handles exactly once, particularly useful in DSL settings where stdcpp run_once support might not be available.
• New API for Thread-Safe Handle Deinitialization: Added TVMFFIEnvHandleDeinitOnce to complement the initialization, ensuring thread-safe, once-only deinitialization of handles.
• Robust Implementation: The implementation leverages platform-specific atomic operations (e.g., InterlockedCompareExchangePointer for MSVC, __atomic_load_n for GCC/Clang) and std::mutex to guarantee thread safety and correct 'once' semantics.
• Comprehensive Testing: Extensive unit tests have been added to cover various scenarios, including successful initialization/deinitialization, idempotency, error handling, and multi-threaded race conditions, ensuring the reliability of the new functions.

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[gemini-code-assist]

Code Review

This pull request introduces thread-safe handle initialization and deinitialization functions, TVMFFIEnvHandleInitOnce and TVMFFIEnvHandleDeinitOnce. The intent is valuable, and the inclusion of comprehensive tests is a great step. However, there are critical flaws in the current implementation. TVMFFIEnvHandleInitOnce employs a single global mutex, which will serialize all initializations and create a significant performance bottleneck. TVMFFIEnvHandleDeinitOnce contains a race condition in its lock-free logic that could lead to severe issues like double-frees. I have provided suggestions to fix these critical problems. There is also a minor naming inconsistency that I've pointed out to improve code clarity.

[tqchen]

/gemini review

[gemini-code-assist]

Code Review

This pull request introduces two new thread-safe helper functions, TVMFFIHandleInitOnce and TVMFFIHandleDeinitOnce, to manage the lifecycle of static handles. The implementation correctly uses a double-checked locking pattern for initialization and an atomic exchange for deinitialization, ensuring thread safety. The changes are accompanied by comprehensive single-threaded and multi-threaded tests. My feedback focuses on improving the clarity of function pointer parameter names in the implementation to align with the public C API header, which will enhance code readability and maintainability.

[tqchen]

/gemini review

[gemini-code-assist]

Code Review

This pull request introduces two new thread-safe helper functions, TVMFFIHandleInitOnce and TVMFFIHandleDeinitOnce, for one-time initialization and deinitialization of static handles. The implementation uses a double-checked locking pattern for initialization and an atomic exchange for deinitialization. The changes also include comprehensive unit tests, covering single-threaded and multi-threaded scenarios.

My review focuses on the thread-safety implementation and test quality. I've identified a potential performance issue in TVMFFIHandleInitOnce due to the use of a single global mutex, which could cause contention. I've also suggested an improvement to the multi-threaded tests to make them more robust. Overall, the changes are well-structured and the new functionality is a useful addition.

[tqchen]

/gemini review

[gemini-code-assist]

Code Review

This pull request introduces TVMFFIHandleInitOnce and TVMFFIHandleDeinitOnce to provide thread-safe initialization and deinitialization of static handles, which is particularly useful for DSLs without native support for this. The implementation uses a double-checked locking pattern with a static mutex for initialization and atomic exchange for deinitialization. The changes are accompanied by a comprehensive set of single-threaded and multi-threaded tests.

The implementation is solid, but I have a couple of suggestions for improvement. The TVMFFIHandleInitOnce function uses a single global mutex, which could become a performance bottleneck if many different handles are initialized concurrently. In the tests, global static variables are used to share state with C-style callbacks, which could be problematic if tests are run in parallel. I've left specific comments with suggestions on how to address these points.