Argument Clinic: Add support for PEP 703's critical sections (Py_BEGIN_CRITICAL_SECTION())

[colesbury]

Feature or enhancement

PEP 703 in large part relies on replacing the GIL with fine grained per-object locks. The primary way to acquire and release these locks is through the critical section API (#111569). It would be helpful if argument clinic could auto generate the API calls in the binding code when specified.

For example, the bufferedio.c will require per-object locking around most calls for thread-safety in --disable-gil builds.

As an example, the _io._Buffered.close function is written as:

cpython/Modules/_io/bufferedio.c

Lines 523 to 529 in 6f09f69

	/*[clinic input]
	_io._Buffered.close
	[clinic start generated code]*/
	static PyObject *
	_io__Buffered_close_impl(buffered *self)
	/*[clinic end generated code: output=7280b7b42033be0c input=d20b83d1ddd7d805]*/

We might add a @critical_section directive to designate that argument clinic should generate Py_BEGIN_CRITICAL_SECTION() and Py_END_CRITICAL_SECTION() in the binding code before calling _io__Buffered_close_impl.

/*[clinic input]
@critical_section
_io._Buffered.close
[clinic start generated code]*/

static PyObject *
_io__Buffered_close_impl(buffered *self)
/*[clinic end generated code: output=7280b7b42033be0c input=d20b83d1ddd7d805]*/

The generated binding code in bufferedio.c.h would then look like:

static PyObject *
_io__Buffered_close(buffered *self, PyObject *Py_UNUSED(ignored))
{
    PyObject *return_value = NULL;

    Py_BEGIN_CRITICAL_SECTION(self);
    return_value = _io__Buffered_close_impl(self);
    Py_END_CRITICAL_SECTION();

    return return_value;
}

Note that Py_BEGIN/END_CRITICAL_SECTION() are no-ops in the default build.

Linked PRs

• gh-111903: Add @critical_section directive to Argument Clinic. #111904
• gh-111903: Update AC to support "pycore_critical_section.h" header #112251

[corona10]

cc @erlend-aasland

[colesbury]

I've updated the issue to use AC's existing "directive" feature and syntax.