8000 [3.6] bpo-31308: If multiprocessing's forkserver dies, launch it agai… · python/cpython@019c99f · GitHub
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[3.6] bpo-31308: If multiprocessing's forkserver dies, launch it again when necessary (GH-3246) (#4252)
* bpo-31308: If multiprocessing's forkserver dies, launch it again when necessary. * Fix test on Windows * Add NEWS entry * Adopt a different approach: ignore SIGINT and SIGTERM, as in semaphore tracker. * Fix comment * Make sure the test doesn't muck with process state * Also test previously-started processes * Update 2017-08-30-17-59-36.bpo-31308.KbexyC.rst * Avoid masking SIGTERM in forkserver. It's not necessary and causes a race condition in test_many_processes.. (cherry picked from commit fc6b348)
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3 files changed

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lines changed

‎Lib/multiprocessing/forkserver.py

Lines changed: 16 additions & 5 deletions
Original file line numberDiff line numberDiff line change
@@ -33,6 +33,7 @@ class ForkServer(object):
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def __init__(self):
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self._forkserver_address = None
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self._forkserver_alive_fd = None
36+
self._forkserver_pid = None
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self._inherited_fds = None
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self._lock = threading.Lock()
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self._preload_modules = ['__main__']
@@ -89,8 +90,17 @@ def ensure_running(self):
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'''
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with self._lock:
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semaphore_tracker.ensure_running()
92-
if self._forkserver_alive_fd is not None:
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return
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if self._forkserver_pid is not None:
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# forkserver was launched before, is it still running?
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pid, status = os.waitpid(self._forkserver_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._forkserver_alive_fd)
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self._forkserver_address = None
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self._forkserver_alive_fd = None
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self._forkserver_pid = None
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cmd = ('from multiprocessing.forkserver import main; ' +
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'main(%d, %d, %r, **%r)')
@@ -127,6 +137,7 @@ def ensure_running(self):
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os.close(alive_r)
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self._forkserver_address = address
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self._forkserver_alive_fd = alive_w
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self._forkserver_pid = pid
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#
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#
@@ -149,11 +160,11 @@ def main(listener_fd, alive_r, preload, main_path=None, sys_path=None):
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util._close_stdin()
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# ignoring SIGCHLD means no need to reap zombie processes;
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# letting SIGINT through avoids KeyboardInterrupt tracebacks
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handlers = {
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# no need to reap zombie processes;
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signal.SIGCHLD: signal.SIG_IGN,
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signal.SIGINT: signal.SIG_DFL,
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# protect the process from ^C
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signal.SIGINT: signal.SIG_IGN,
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}
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old_handlers = {sig: signal.signal(sig, val)
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for (sig, val) in handlers.items()}

‎Lib/test/_test_multiprocessing.py

Lines changed: 48 additions & 0 deletions
Original file line numberDiff line numberDiff line change
@@ -446,6 +446,54 @@ def test_error_on_stdio_flush(self):
446446
finally:
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setattr(sys, stream_name, old_stream)
448448

449+
@classmethod
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def _sleep_and_set_event(self, evt, delay=0.0):
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time.sleep(delay)
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evt.set()
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def check_forkserver_death(self, signum):
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# bpo-31308: if the forkserver process has died, we should still
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# be able to create and run new Process instances (the forkserver
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# is implicitly restarted).
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if self.TYPE == 'threads':
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self.skipTest('test not appropriate for {}'.format(self.TYPE))
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sm = multiprocessing.get_start_method()
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if sm != 'forkserver':
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# The fork method by design inherits all fds from the parent,
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# trying to go against it is a lost battle
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self.skipTest('test not appropriate for {}'.format(sm))
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466+
from multiprocessing.forkserver import _forkserver
467+
_forkserver.ensure_running()
468+
469+
evt = self.Event()
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proc = self.Process(target=self._sleep_and_set_event, args=(evt, 1.0))
471+
proc.start()
4 8000 72+
473+
pid = _forkserver._forkserver_pid
474+
os.kill(pid, signum)
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time.sleep(1.0) # give it time to die
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477+
evt2 = self.Event()
478+
proc2 = self.Process(target=self._sleep_and_set_event, args=(evt2,))
479+
proc2.start()
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proc2.join()
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self.assertTrue(evt2.is_set())
482+
self.assertEqual(proc2.exitcode, 0)
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484+
proc.join()
485+
self.assertTrue(evt.is_set())
486+
self.assertIn(proc.exitcode, (0, 255))
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488+
def test_forkserver_sigint(self):
489+
# Catchable signal
490+
self.check_forkserver_death(signal.SIGINT)
491+
492+
def test_forkserver_sigkill(self):
493+
# Uncatchable signal
494+
if os.name != 'nt':
495+
self.check_forkserver_death(signal.SIGKILL)
496+
449497

450498
#
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#

‎Misc/NEWS.d/next/Library/2017-08-30-17-59-36.bpo-31308.KbexyC.rst

Lines changed: 2 additions & 0 deletions
Original file line numberDiff line numberDiff line change
@@ -0,0 +1,2 @@
1+
Make multiprocessing's forkserver process immune to Ctrl-C and other user interruptions.
2+
If it crashes, restart it when necessary.

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