posixmodule uses PyOS_setsig to save & restore signal handlers

[encukou]

posixmodule ignores signals in os_openpty_impl and os_grantpt_impl by wrapping them in two PyOS_setsig calls:

   sig_saved = PyOS_setsig(SIGCHLD, SIG_DFL);
    ...
    PyOS_setsig(SIGCHLD, sig_saved);

This relies on the GIL being held, so it probably needs a dedicated lock in free-threading builds.

Linked PRs

• gh-114727: Update os_{openpty|grantpt}_impl to use per module lock. #117017

[corona10]

@colesbury @erlend-aasland
Hmm, Do we need something like per signal API lock for the interpreter-wide that acquires lock when we need to call PyOS_setsig at any moment?

For example, if any thread needs to call PyOS_setsig or PyOS_getsig, is it required to acquire the specific interpreter-wise lock?

Py_BEGIN_CRITICAL_SECTION(interp->signal);
PyOS_setsig
..

PyOS_getsig
...
Py_END_CRITCIAL_SECTION();

And then add assertion(_Py_CRITICAL_SECTION_ASSERT_OBJECT_LOCKED) inside of PyOS_setsig abnd PyOS_getsig

Or instead we can use lightweight locking API for the same purpose.

note: IIUC, PyOS_setsig is process-wide.