cpython/Lib/test/fork_wait.py

"""This test case provides support for checking forking and wait behavior.

To test different wait behavior, override the wait_impl method.

We want fork1() semantics -- only the forking thread survives in the
child after a fork().

On some systems (e.g. Solaris without posix threads) we find that all
active threads survive in the child after a fork(); this is an error.
"""

import os, sys, time, unittest
import threading
from test import support
from test.support import threading_helper


LONGSLEEP = 2
SHORTSLEEP = 0.5
NUM_THREADS = 4

class ForkWait(unittest.TestCase):

    def setUp(self):
        self._threading_key = threading_helper.threading_setup()
        self.alive = {}
        self.stop = 0
        self.threads = []

    def tearDown(self):
        # Stop threads
        self.stop = 1
        for thread in self.threads:
            thread.join()
        thread = None
        self.threads.clear()
        threading_helper.threading_cleanup(*self._threading_key)

    def f(self, id):
        while not self.stop:
            self.alive[id] = os.getpid()
            try:
                time.sleep(SHORTSLEEP)
            except OSError:
                pass

    def wait_impl(self, cpid, *, exitcode):
        support.wait_process(cpid, exitcode=exitcode)

    def test_wait(self):
        for i in range(NUM_THREADS):
            thread = threading.Thread(target=self.f, args=(i,))
            thread.start()
            self.threads.append(thread)

        # busy-loop to wait for threads
        for _ in support.sleeping_retry(support.SHORT_TIMEOUT):
            if len(self.alive) >= NUM_THREADS:
                break

        a = sorted(self.alive.keys())
        self.assertEqual(a, list(range(NUM_THREADS)))

        prefork_lives = self.alive.copy()

        if sys.platform in ['unixware7']:
            cpid = os.fork1()
        else:
            cpid = os.fork()

        if cpid == 0:
            # Child
            time.sleep(LONGSLEEP)
            n = 0
            for key in self.alive:
                if self.alive[key] != prefork_lives[key]:
                    n += 1
            os._exit(n)
        else:
            # Parent
            self.wait_impl(cpid, exitcode=0)