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 test.support as support
_thread = support.import_module('_thread')

LONGSLEEP = 2
SHORTSLEEP = 0.5
NUM_THREADS = 4

class ForkWait(unittest.TestCase):

    def setUp(self):
        self.alive = {}
        self.stop = 0

    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):
        for i in range(10):
            # waitpid() shouldn't hang, but some of the buildbots seem to hang
            # in the forking tests.  This is an attempt to fix the problem.
            spid, status = os.waitpid(cpid, os.WNOHANG)
            if spid == cpid:
                break
            time.sleep(2 * SHORTSLEEP)

        self.assertEqual(spid, cpid)
        self.assertEqual(status, 0, "cause = %d, exit = %d" % (status&0xff, status>>8))

    @support.reap_threads
    def test_wait(self):
        for i in range(NUM_THREADS):
            _thread.start_new(self.f, (i,))

        # busy-loop to wait for threads
        deadline = time.monotonic() + 10.0
        while len(self.alive) < NUM_THREADS:
            time.sleep(0.1)
            if deadline < time.monotonic():
                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
            try:
                self.wait_impl(cpid)
            finally:
                # Tell threads to die
                self.stop = 1