8000 bpo-31804: Fix multiprocessing.Process with broken standard streams (… · python/cpython@e756f66 · GitHub
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pitroupitrou
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bpo-31804: Fix multiprocessing.Process with broken standard streams (#6079)
In some conditions the standard streams will be None or closed in the child process (for example if using "pythonw" instead of "python" on Windows). Avoid failing with a non-0 exit code in those conditions. Report and initial patch by poxthegreat.
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5 files changed

+47
-12
lines changed

5 files changed

+47
-12
lines changed

‎Lib/multiprocessing/popen_fork.py

Lines changed: 1 addition & 8 deletions
Original file line numberDiff line numberDiff line change
@@ -14,14 +14,7 @@ class Popen(object):
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method = 'fork'
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def __init__(self, process_obj):
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try:
18-
sys.stdout.flush()
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except (AttributeError, ValueError):
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pass
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try:
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sys.stderr.flush()
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except (AttributeError, ValueError):
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pass
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util._flush_std_streams()
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self.returncode = None
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self.finalizer = None
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self._launch(process_obj)

‎Lib/multiprocessing/process.py

Lines changed: 1 addition & 2 deletions
Original file line numberDiff line numberDiff line change
@@ -314,8 +314,7 @@ def _bootstrap(self):
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finally:
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threading._shutdown()
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util.info('process exiting with exitcode %d' % exitcode)
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sys.stdout.flush()
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sys.stderr.flush()
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util._flush_std_streams()
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return exitcode
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‎Lib/multiprocessing/util.py

Lines changed: 14 additions & 0 deletions
Original file line numberDiff line numberDiff line change
@@ -391,6 +391,20 @@ def _close_stdin():
391391
except (OSError, ValueError):
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pass
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#
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# Flush standard streams, if any
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#
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def _flush_std_streams():
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try:
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sys.stdout.flush()
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except (AttributeError, ValueError):
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pass
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try:
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sys.stderr.flush()
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except (AttributeError, ValueError):
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pass
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394408
#
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# Start a program with only specified fds kept open
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#

‎Lib/test/_test_multiprocessing.py

Lines changed: 29 additions & 2 deletions
Original file line numberDiff line numberDiff line change
@@ -584,10 +584,19 @@ def test_wait_for_threads(self):
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self.assertTrue(evt.is_set())
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586586
@classmethod
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def _test_error_on_stdio_flush(self, evt):
587+
def _test_error_on_stdio_flush(self, evt, break_std_streams={}):
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for stream_name, action in break_std_streams.items():
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if action == 'close':
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stream = io.StringIO()
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stream.close()
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else:
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assert action == 'remove'
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stream = None
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setattr(sys, stream_name, None)
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evt.set()
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590-
def test_error_on_stdio_flush(self):
598+
def test_error_on_stdio_flush_1(self):
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# Check that Process works with broken standard streams
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streams = [io.StringIO(), None]
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streams[0].close()
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for stream_name in ('stdout', 'stderr'):
@@ -601,6 +610,24 @@ def test_error_on_stdio_flush(self):
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proc.start()
602611
proc.join()
603612
self.assertTrue(evt.is_set())
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self.assertEqual(proc.exitcode, 0)
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finally:
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setattr(sys, stream_name, old_stream)
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617+
def test_error_on_stdio_flush_2(self):
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# Same as test_error_on_stdio_flush_1(), but standard streams are
619+
# broken by the child process
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for stream_name in ('stdout', 'stderr'):
621+
for action in ('close', 'remove'):
622+
old_stream = getattr(sys, stream_name)
623+
try:
624+
evt = self.Event()
625+
proc = self.Process(target=self._test_error_on_stdio_flush,
626+
args=(evt, {stream_name: action}))
627+
proc.start()
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proc.join()
629+
self.assertTrue(evt.is_set())
630+
self.assertEqual(proc.exitcode, 0)
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finally:
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setattr(sys, stream_name, old_stream)
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‎Misc/NEWS.d/next/Library/2018-03-11-19-03-52.bpo-31804.i8KUMp.rst

Lines changed: 2 additions & 0 deletions
Original file line numberDiff line numberDiff line change
@@ -0,0 +1,2 @@
1+
Avoid failing in multiprocessing.Process if the standard streams are closed
2+
or None at exit.

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