gh-131913: multiprocessing: add interrupt for POSIX

[pulkin]

• Issue: Add multiprocessing.Process.interrupt #131913

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📚 Documentation preview 📚: https://cpython-previews--132453.org.readthedocs.build/en/132453/library/multiprocessing.html#multiprocessing.Process.interrupt

[picnixz]

Can you add a test where we register a signal.signal handler?

[picnixz]

Does it use TerminateProcess()?

[picnixz]

This needs a better wording. In addition, a whatsnew/3.14.rst entry must be created as well.

[picnixz]

Suggested change

	def test_interrupt(self):
	if os.name != 'nt':
	exitcode = self._kill_process(multiprocessing.Process.interrupt)
	self.assertEqual(exitcode, 1)
	@unittest.skipIf(os.name == 'nt', "POSIX only")
	def test_interrupt(self):
	exitcode = self._kill_process(multiprocessing.Process.interrupt)
	self.assertEqual(exitcode, 1)

Can we exit with a SIGINT value instead? or will it always be 1?

[pulkin]

I believe we can exit with SIGINT if we unset the signal handler in the child process

from signal import *
signal(SIGINT, SIG_DFL)

I expect this will make it behave similarly to SIGTERM or SIGKILL.

[picnixz]

We should still use self.assertEqual(exitcode, signal.SIGINT) by default (at least for the test suite).

[pulkin]

I think it is a good idea for the test suite to actually check against exit code 1 which is the default behavior.

interrupt() triggers a default_int_handler in the child process which raises KeyboardInterrupt which, in turn, will probably be processed in this chunk setting exit code to 1

https://github.com/python/cpython/blob/main/Lib/multiprocessing/process.py#L323-L327

Achieving this behavior is a major motivation for the change.

[picnixz]

Oh so there is an explicit value being used here. Can you actually add a comment about this as well? so that we know that Python is explicitly setting the exit code to 1. TiA.

[pulkin]

I added a unit test with SIGINT handler unset, a comment in the above test about exit code 1 and some hints in the docs about how it works with exceptions and exit codes.