gh-116738: Add critical section to dbm/gdbm context manager

[yoney]

Add Py_{BEGIN,END}_CRITICAL_SECTION() to the context managers in the dbm and gdbm modules for the free threading build. Other methods are already covered.

This could be a problem in a rare corner case if a thread outlives the context manager's scope. I created a local test, and TSAN identifies the issue.

    def test_context_manager(self):
        def worker(db):
            db.close()

        with os_helper.temp_dir() as tmpdirname:
            with gdbm.open(f"{tmpdirname}/gdbm_filename", "c") as db:
                t1 = threading.Thread(target=worker, args=(db,))
                t1.start()

        t1.join()

WARNING: ThreadSanitizer: data race (pid=1672837)
  Read of size 8 at 0x7f9fdb330e48 by thread T1:
    #0 _gdbm_gdbm_close_impl /home/alper/workspace/tsan/./Modules/_gdbmmodule.c:413:15 (_gdbm.cpython-315td-x86_64-linux-gnu.so+0x2ce1) (BuildId: 42fff9900c3973fef01c9a778b42049ab0110b9f)
    #1 _gdbm_gdbm_close /home/alper/workspace/tsan/./Modules/clinic/_gdbmmodule.c.h:100:20 (_gdbm.cpython-315td-x86_64-linux-gnu.so+0x2ce1)
    #2 method_vectorcall_NOARGS /home/alper/workspace/tsan/Objects/descrobject.c:448:24 (python+0x5c662b) (BuildId: 89128bd333556519224b9af239856b3fcb80f8ab)
...

  Previous write of size 8 at 0x7f9fdb330e48 by main thread:
    #0 _gdbm_gdbm_close_impl /home/alper/workspace/tsan/./Modules/_gdbmmodule.c:416:18 (_gdbm.cpython-315td-x86_64-linux-gnu.so+0x4944) (BuildId: 42fff9900c3973fef01c9a778b42049ab0110b9f)
    #1 gdbm__exit__ /home/alper/workspace/tsan/./Modules/_gdbmmodule.c:693:12 (_gdbm.cpython-315td-x86_64-linux-gnu.so+0x4944)
    #2 method_vectorcall_VARARGS /home/alper/workspace/tsan/Objects/descrobject.c:325:24 (python+0x5c5ef9) (BuildId: 89128bd333556519224b9af239856b3fcb80f8ab)
...

SUMMARY: ThreadSanitizer: data race /home/alper/workspace/tsan/./Modules/_gdbmmodule.c:413:15 in _gdbm_gdbm_close_impl
==================    

cc: @mpage @colesbury

• Issue: Audit all built-in modules for thread safety #116738

[serhiy-storchaka]

LGTM. 👍

[colesbury]

LGTM as well.

FYI, you can also use Argument Clinic for __enter__ and __exit__ functions now if you prefer Argument Clinic boilerplate to Py_BEGIN_CRITICAL_SECTION boilerplate.

[miss-islington-app]

Thanks @yoney for the PR, and @colesbury for merging it 🌮🎉.. I'm working now to backport this PR to: 3.14.
🐍🍒⛏🤖

[bedevere-app]

GH-140459 is a backport of this pull request to the 3.14 branch.