mirror of https://github.com/python/cpython
bpo-31310: multiprocessing's semaphore tracker should be launched again if crashed (#3247)
* bpo-31310: multiprocessing's semaphore tracker should be launched again if crashed * Avoid mucking with process state in test. Add a warning if the semaphore process died, as semaphores may then be leaked. * Add NEWS entry
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@ -29,6 +29,7 @@ class SemaphoreTracker(object):
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def __init__(self):
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self._lock = threading.Lock()
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self._fd = None
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self._pid = None
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def getfd(self):
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self.ensure_running()
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@ -40,8 +41,20 @@ class SemaphoreTracker(object):
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This can be run from any process. Usually a child process will use
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the semaphore created by its parent.'''
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with self._lock:
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if self._fd is not None:
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return
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if self._pid is not None:
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# semaphore tracker was launched before, is it still running?
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pid, status = os.waitpid(self._pid, os.WNOHANG)
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if not pid:
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# => still alive
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return
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# => dead, launch it again
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os.close(self._fd)
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self._fd = None
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self._pid = None
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warnings.warn('semaphore_tracker: process died unexpectedly, '
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'relaunching. Some semaphores might leak.')
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fds_to_pass = []
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try:
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fds_to_pass.append(sys.stderr.fileno())
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@ -55,12 +68,13 @@ class SemaphoreTracker(object):
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exe = spawn.get_executable()
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args = [exe] + util._args_from_interpreter_flags()
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args += ['-c', cmd % r]
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util.spawnv_passfds(exe, args, fds_to_pass)
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pid = util.spawnv_passfds(exe, args, fds_to_pass)
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except:
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os.close(w)
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raise
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else:
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self._fd = w
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self._pid = pid
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finally:
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os.close(r)
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@ -4,6 +4,7 @@
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import unittest
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import queue as pyqueue
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import contextlib
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import time
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import io
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import itertools
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@ -4344,14 +4345,14 @@ class TestStartMethod(unittest.TestCase):
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self.fail("failed spawning forkserver or grandchild")
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#
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# Check that killing process does not leak named semaphores
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#
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@unittest.skipIf(sys.platform == "win32",
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"test semantics don't make sense on Windows")
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class TestSemaphoreTracker(unittest.TestCase):
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def test_semaphore_tracker(self):
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#
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# Check that killing process does not leak named semaphores
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#
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import subprocess
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cmd = '''if 1:
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import multiprocessing as mp, time, os
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@ -4385,6 +4386,40 @@ class TestSemaphoreTracker(unittest.TestCase):
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self.assertRegex(err, expected)
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self.assertRegex(err, r'semaphore_tracker: %r: \[Errno' % name1)
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def check_semaphore_tracker_death(self, signum, should_die):
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# bpo-31310: if the semaphore tracker process has died, it should
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# be restarted implicitly.
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from multiprocessing.semaphore_tracker import _semaphore_tracker
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_semaphore_tracker.ensure_running()
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pid = _semaphore_tracker._pid
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os.kill(pid, signum)
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time.sleep(1.0) # give it time to die
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ctx = multiprocessing.get_context("spawn")
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with contextlib.ExitStack() as stack:
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if should_die:
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stack.enter_context(self.assertWarnsRegex(
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UserWarning,
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"semaphore_tracker: process died"))
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sem = ctx.Semaphore()
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sem.acquire()
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sem.release()
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wr = weakref.ref(sem)
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# ensure `sem` gets collected, which triggers communication with
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# the semaphore tracker
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del sem
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gc.collect()
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self.assertIsNone(wr())
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def test_semaphore_tracker_sigint(self):
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# Catchable signal (ignored by semaphore tracker)
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self.check_semaphore_tracker_death(signal.SIGINT, False)
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def test_semaphore_tracker_sigkill(self):
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# Uncatchable signal.
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self.check_semaphore_tracker_death(signal.SIGKILL, True)
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class TestSimpleQueue(unittest.TestCase):
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@classmethod
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@ -0,0 +1 @@
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multiprocessing's semaphore tracker should be launched again if crashed.
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