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Merged
asvetlov merged 1 commit into from
May 20, 2018
Merged

bpo-26819: Prevent proactor double read on resume #6921

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8 changes: 7 additions & 1 deletion Lib/asyncio/proactor_events.py
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Original file line number Diff line number Diff line change
Expand Up @@ -161,6 +161,7 @@ def __init__(self, loop, sock, protocol, waiter=None,
extra=None, server=None):
super().__init__(loop, sock, protocol, waiter, extra, server)
self._paused = False
self._reschedule_on_resume = False

if protocols._is_buffered_protocol(protocol):
self._loop_reading = self._loop_reading__get_buffer
Expand All @@ -180,6 +181,7 @@ def pause_reading(self):
if self._read_fut is not None and not self._read_fut.done():
self._read_fut.cancel()
self._read_fut = None
self._reschedule_on_resume = True

if self._loop.get_debug():
logger.debug("%r pauses reading", self)
Expand All @@ -188,7 +190,9 @@ def resume_reading(self):
if self._closing or not self._paused:
return
self._paused = False
self._loop.call_soon(self._loop_reading, self._read_fut)
if self._reschedule_on_resume:
self._loop.call_soon(self._loop_reading, self._read_fut)
self._reschedule_on_resume = False
if self._loop.get_debug():
logger.debug("%r resumes reading", self)

Expand All @@ -208,6 +212,7 @@ def _loop_reading__on_eof(self):

def _loop_reading__data_received(self, fut=None):
if self._paused:
self._reschedule_on_resume = True
return

data = None
Expand Down Expand Up @@ -257,6 +262,7 @@ def _loop_reading__data_received(self, fut=None):

def _loop_reading__get_buffer(self, fut=None):
if self._paused:
self._reschedule_on_resume = True
return

nbytes = None
Expand Down
9 changes: 8 additions & 1 deletion Lib/test/test_asyncio/test_proactor_events.py
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Original file line number Diff line number Diff line change
Expand Up @@ -334,7 +334,7 @@ def test_write_eof_duplex_pipe(self):
def test_pause_resume_reading(self):
tr = self.socket_transport()
futures = []
for msg in [b'data1', b'data2', b'data3', b'data4', b'']:
for msg in [b'data1', b'data2', b'data3', b'data4', b'data5', b'']:
f = asyncio.Future(loop=self.loop)
f.set_result(msg)
futures.append(f)
Expand Down Expand Up @@ -364,6 +364,13 @@ def test_pause_resume_reading(self):
self.protocol.data_received.assert_called_with(b'data3')
self.loop._run_once()
self.protocol.data_received.assert_called_with(b'data4')

tr.pause_reading()
tr.resume_reading()
self.loop.call_exception_handler = mock.Mock()
self.loop._run_once()
self.loop.call_exception_handler.assert_not_called()
self.protocol.data_received.assert_called_with(b'data5')
tr.close()

self.assertFalse(tr.is_reading())
Expand Down
2 changes: 2 additions & 0 deletions Misc/NEWS.d/next/Library/2018-05-16-05-24-43.bpo-26819.taxbVT.rst
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Original file line number Diff line number Diff line change
@@ -0,0 +1,2 @@
Fix race condition with `ReadTransport.resume_reading` in Windows proactor
event loop.