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Issue #25233: Rewrite the guts of Queue to be more understandable and correct.

This commit is contained in:
Guido van Rossum 2015-09-28 07:42:34 -07:00
parent 16a1f28194
commit 99f96c5451
3 changed files with 91 additions and 118 deletions
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152
Lib/asyncio/queues.py
View File

@ -47,7 +47,7 @@ class Queue:
# Futures.
self._getters = collections.deque()
# Futures
# Futures.
self._putters = collections.deque()
self._unfinished_tasks = 0
self._finished = locks.Event(loop=self._loop)
@ -67,10 +67,13 @@ class Queue:
# End of the overridable methods.
def __put_internal(self, item):
self._put(item)
self._unfinished_tasks += 1
self._finished.clear()
def _wakeup_next(self, waiters):
# Wake up the next waiter (if any) that isn't cancelled.
while waiters:
waiter = waiters.popleft()
if not waiter.done():
waiter.set_result(None)
break
def __repr__(self):
return '<{} at {:#x} {}>'.format(
@ -91,16 +94,6 @@ class Queue:
result += ' tasks={}'.format(self._unfinished_tasks)
return result
def _consume_done_getters(self):
# Delete waiters at the head of the get() queue who've timed out.
while self._getters and self._getters[0].done():
self._getters.popleft()
def _consume_done_putters(self):
# Delete waiters at the head of the put() queue who've timed out.
while self._putters and self._putters[0].done():
self._putters.popleft()
def qsize(self):
"""Number of items in the queue."""
return len(self._queue)
@ -134,47 +127,31 @@ class Queue:
This method is a coroutine.
"""
self._consume_done_getters()
if self._getters:
assert not self._queue, (
'queue non-empty, why are getters waiting?')
getter = self._getters.popleft()
self.__put_internal(item)
# getter cannot be cancelled, we just removed done getters
getter.set_result(self._get())
elif self._maxsize > 0 and self._maxsize <= self.qsize():
waiter = futures.Future(loop=self._loop)
self._putters.append(waiter)
yield from waiter
self._put(item)
else:
self.__put_internal(item)
while self.full():
putter = futures.Future(loop=self._loop)
self._putters.append(putter)
try:
yield from putter
except:
putter.cancel() # Just in case putter is not done yet.
if not self.full() and not putter.cancelled():
# We were woken up by get_nowait(), but can't take
# the call. Wake up the next in line.
self._wakeup_next(self._putters)
raise
return self.put_nowait(item)
def put_nowait(self, item):
"""Put an item into the queue without blocking.
If no free slot is immediately available, raise QueueFull.
"""
self._consume_done_getters()
if self._getters:
assert not self._queue, (
'queue non-empty, why are getters waiting?')
getter = self._getters.popleft()
self.__put_internal(item)
# getter cannot be cancelled, we just removed done getters
getter.set_result(self._get())
elif self._maxsize > 0 and self._maxsize <= self.qsize():
if self.full():
raise QueueFull
else:
self.__put_internal(item)
self._put(item)
self._unfinished_tasks += 1
self._finished.clear()
self._wakeup_next(self._getters)
@coroutine
def get(self):
@ -184,77 +161,30 @@ class Queue:
This method is a coroutine.
"""
self._consume_done_putters()
if self._putters:
assert self.full(), 'queue not full, why are putters waiting?'
putter = self._putters.popleft()
# When a getter runs and frees up a slot so this putter can
# run, we need to defer the put for a tick to ensure that
# getters and putters alternate perfectly. See
# ChannelTest.test_wait.
self._loop.call_soon(putter._set_result_unless_cancelled, None)
return self._get()
elif self.qsize():
return self._get()
else:
waiter = futures.Future(loop=self._loop)
self._getters.append(waiter)
while self.empty():
getter = futures.Future(loop=self._loop)
self._getters.append(getter)
try:
return (yield from waiter)
except futures.CancelledError:
# if we get CancelledError, it means someone cancelled this
# get() coroutine. But there is a chance that the waiter
# already is ready and contains an item that has just been
# removed from the queue. In this case, we need to put the item
# back into the front of the queue. This get() must either
# succeed without fault or, if it gets cancelled, it must be as
# if it never happened.
if waiter.done():
self._put_it_back(waiter.result())
yield from getter
except:
getter.cancel() # Just in case getter is not done yet.
if not self.empty() and not getter.cancelled():
# We were woken up by put_nowait(), but can't take
# the call. Wake up the next in line.
self._wakeup_next(self._getters)
raise
def _put_it_back(self, item):
"""
This is called when we have a waiter to get() an item and this waiter
gets cancelled. In this case, we put the item back: wake up another
waiter or put it in the _queue.
"""
self._consume_done_getters()
if self._getters:
assert not self._queue, (
'queue non-empty, why are getters waiting?')
getter = self._getters.popleft()
self.__put_internal(item)
# getter cannot be cancelled, we just removed done getters
getter.set_result(item)
else:
self._queue.appendleft(item)
return self.get_nowait()
def get_nowait(self):
"""Remove and return an item from the queue.
Return an item if one is immediately available, else raise QueueEmpty.
"""
self._consume_done_putters()
if self._putters:
assert self.full(), 'queue not full, why are putters waiting?'
putter = self._putters.popleft()
# Wake putter on next tick.
# getter cannot be cancelled, we just removed done putters
putter.set_result(None)
return self._get()
elif self.qsize():
return self._get()
else:
if self.empty():
raise QueueEmpty
item = self._get()
self._wakeup_next(self._putters)
return item
def task_done(self):
"""Indicate that a formerly enqueued task is complete.

55
Lib/test/test_asyncio/test_queues.py
View File

@ -271,6 +271,29 @@ class QueueGetTests(_QueueTestBase):
self.assertEqual(self.loop.run_until_complete(q.get()), 'a')
self.assertEqual(self.loop.run_until_complete(q.get()), 'b')
def test_why_are_getters_waiting(self):
# From issue #268.
@asyncio.coroutine
def consumer(queue, num_expected):
for _ in range(num_expected):
yield from queue.get()
@asyncio.coroutine
def producer(queue, num_items):
for i in range(num_items):
yield from queue.put(i)
queue_size = 1
producer_num_items = 5
q = asyncio.Queue(queue_size, loop=self.loop)
self.loop.run_until_complete(
asyncio.gather(producer(q, producer_num_items),
consumer(q, producer_num_items),
loop=self.loop),
)
class QueuePutTests(_QueueTestBase):
@ -377,13 +400,8 @@ class QueuePutTests(_QueueTestBase):
loop.run_until_complete(reader3)
# reader2 will receive `2`, because it was added to the
# queue of pending readers *before* put_nowaits were called.
self.assertEqual(reader2.result(), 2)
# reader3 will receive `1`, because reader1 was cancelled
# before is had a chance to execute, and `2` was already
# pushed to reader2 by second `put_nowait`.
self.assertEqual(reader3.result(), 1)
# It is undefined in which order concurrent readers receive results.
self.assertEqual({reader2.result(), reader3.result()}, {1, 2})
def test_put_cancel_drop(self):
@ -479,6 +497,29 @@ class QueuePutTests(_QueueTestBase):
self.loop.run_until_complete(q.put('a'))
self.assertEqual(self.loop.run_until_complete(t), 'a')
def test_why_are_putters_waiting(self):
# From issue #265.
queue = asyncio.Queue(2, loop=self.loop)
@asyncio.coroutine
def putter(item):
yield from queue.put(item)
@asyncio.coroutine
def getter():
yield
num = queue.qsize()
for _ in range(num):
item = queue.get_nowait()
t0 = putter(0)
t1 = putter(1)
t2 = putter(2)
t3 = putter(3)
self.loop.run_until_complete(
asyncio.gather(getter(), t0, t1, t2, t3, loop=self.loop))
class LifoQueueTests(_QueueTestBase):

2
Misc/NEWS
View File

@ -81,6 +81,8 @@ Core and Builtins
Library
-------
- Issue #25233: Rewrite the guts of Queue to be more understandable and correct.
- Issue #23600: Default implementation of tzinfo.fromutc() was returning
wrong results in some cases.