Leave/enter Python execution (GIL)

HPyThreadState HPy_LeavePythonExecution(HPyContext *ctx)
void HPy_ReenterPythonExecution(HPyContext *ctx, HPyThreadState state)

Leaving Python execution: for releasing GIL and other use-cases.

In most situations, users should prefer using convenience macros: HPy_BEGIN_LEAVE_PYTHON(context)/HPy_END_LEAVE_PYTHON(context)

HPy extensions may leave Python execution when running Python independent code: long-running computations or blocking operations. When an extension has left the Python execution it must not call any HPy API other than HPy_ReenterPythonExecution. It can access pointers returned by HPy API, e.g., HPyUnicode_AsUTF8String, provided that they are valid at the point of calling HPy_LeavePythonExecution.

Python execution must be reentered on the same thread as where it was left. The leave/enter calls must not be nested. Debug mode will, in the future, enforce these constraints.

Python implementations may use this knowledge however they wish. The most obvious use case is to release the GIL, in which case the HPy_BEGIN_LEAVE_PYTHON/HPy_END_LEAVE_PYTHON becomes equivalent to Py_BEGIN_ALLOW_THREADS/Py_END_ALLOW_THREADS.