gh-116738: Make syslog module thread-safe

[yoney]

Make the setlogmask() function in the syslog module thread-safe. These changes are relevant for scenarios where the GIL is disabled or when using subinterpreters.

• The functions syslog(), openlog(), and closelog() in the syslog module are already handled for FT-Python using the @critical_section on the module. However, there might be an issue with syslog() for subinterpreters on macOS.

cpython/Modules/syslogmodule.c

Lines 242 to 245 in 03017a8

	#ifdef__APPLE__
	// gh-98178: On macOS, libc syslog() is not thread-safe
	syslog(priority, "%s", message);
	#else

I will check/test the macOS subinterpreter and create a separate PR if necessary.

• Linux man page (3): setlogmast()

cc: @mpage@colesbury

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

[mpage]

LGTM!

[aisk]

I'm wondering whether these functions are thread safe on other UNIX-like platforms, but I found that on some BSDs (OpenBSD¹ and NetBSD) and on AIX², some of these syslog related functions are not thread safe, and they provide alternative versions with the _r suffix.

I'm not sure whether we should add locks for these functions on these platforms, or change the implementations to the _r versions.

But these platforms are not marked as supported in PEP11³, so I think this is may not be a big issue for now.

Footnotes

1. https://man.freebsd.org/cgi/man.cgi?query=syslog&apropos=0&sektion=3&manpath=OpenBSD+7.7&arch=default&format=html↩

2. https://www.ibm.com/docs/en/aix/7.3.0?topic=s-syslog-openlog-closelog-setlogmask-subroutine↩

3. https://peps.python.org/pep-0011/↩

[mpage]

@aisk - I think the current implementation should be thread-safe on those platforms on both builds. The GIL provides thread safety on the default build; a critical section provides thread-safety on the free-threaded builds. There is one notable exception, syslog, which @yoney just pointed out to me releases the GIL/CS around the call to syslog:

cpython/Modules/syslogmodule.c

Lines 242 to 249 in 5f9e38f

	#ifdef__APPLE__
	// gh-98178: On macOS, libc syslog() is not thread-safe
	syslog(priority, "%s", message);
	#else
	Py_BEGIN_ALLOW_THREADS;
	syslog(priority, "%s", message);
	Py_END_ALLOW_THREADS;
	#endif

I think we can address that in a follow up, if needed.