# Copyright 2015 The Tornado Authors
#
# Licensed under the Apache License, Version 2.0 (the "License"); you may
# not use this file except in compliance with the License. You may obtain
# a copy of the License at
#
# http://www.apache.org/licenses/LICENSE-2.0
#
# Unless required by applicable law or agreed to in writing, software
# distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
# WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the
# License for the specific language governing permissions and limitations
# under the License.
"""Asynchronous queues for coroutines. These classes are very similar
to those provided in the standard library's `asyncio package
<https://docs.python.org/3/library/asyncio-queue.html>`_.
.. warning::
Unlike the standard library's `queue` module, the classes defined here
are *not* thread-safe. To use these queues from another thread,
use `.IOLoop.add_callback` to transfer control to the `.IOLoop` thread
before calling any queue methods.
"""
from __future__ import absolute_import, division, print_function
import collections
import heapq
from tornado import gen, ioloop
from tornado.concurrent import Future, future_set_result_unless_cancelled
from tornado.locks import Event
__all__ = ['Queue', 'PriorityQueue', 'LifoQueue', 'QueueFull', 'QueueEmpty']
class QueueEmpty(Exception):
"""Raised by `.Queue.get_nowait` when the queue has no items."""
pass
class QueueFull(Exception):
"""Raised by `.Queue.put_nowait` when a queue is at its maximum size."""
pass
def _set_timeout(future, timeout):
if timeout:
def on_timeout():
if not future.done():
future.set_exception(gen.TimeoutError())
io_loop = ioloop.IOLoop.current()
timeout_handle = io_loop.add_timeout(timeout, on_timeout)
future.add_done_callback(
lambda _: io_loop.remove_timeout(timeout_handle))
class _QueueIterator(object):
def __init__(self, q):
self.q = q
def __anext__(self):
return self.q.get()
class Queue(object):
"""Coordinate producer and consumer coroutines.
If maxsize is 0 (the default) the queue size is unbounded.
.. testcode::
from tornado import gen
from tornado.ioloop import IOLoop
from tornado.queues import Queue
q = Queue(maxsize=2)
async def consumer():
async for item in q:
try:
print('Doing work on %s' % item)
await gen.sleep(0.01)
finally:
q.task_done()
async def producer():
for item in range(5):
await q.put(item)
print('Put %s' % item)
async def main():
# Start consumer without waiting (since it never finishes).
IOLoop.current().spawn_callback(consumer)
await producer() # Wait for producer to put all tasks.
await q.join() # Wait for consumer to finish all tasks.
print('Done')
IOLoop.current().run_sync(main)
.. testoutput::
Put 0
Put 1
Doing work on 0
Put 2
Doing work on 1
Put 3
Doing work on 2
Put 4
Doing work on 3
Doing work on 4
Done
In versions of Python without native coroutines (before 3.5),
``consumer()`` could be written as::
@gen.coroutine
def consumer():
while True:
item = yield q.get()
try:
print('Doing work on %s' % item)
yield gen.sleep(0.01)
finally:
q.task_done()
.. versionchanged:: 4.3
Added ``async for`` support in Python 3.5.
"""
def __init__(self, maxsize=0):
if maxsize is None:
raise TypeError("maxsize can't be None")
if maxsize < 0:
raise ValueError("maxsize can't be negative")
self._maxsize = maxsize
self._init()
self._getters = collections.deque([]) # Futures.
self._putters = collections.deque([]) # Pairs of (item, Future).
self._unfinished_tasks = 0
self._finished = Event()
self._finished.set()
@property
def maxsize(self):
"""Number of items allowed in the queue."""
return self._maxsize
def qsize(self):
"""Number of items in the queue."""
return len(self._queue)
def empty(self):
return not self._queue
def full(self):
if self.maxsize == 0:
return False
else:
return self.qsize() >= self.maxsize
def put(self, item, timeout=None):
"""Put an item into the queue, perhaps waiting until there is room.
Returns a Future, which raises `tornado.util.TimeoutError` after a
timeout.
``timeout`` may be a number denoting a time (on the same
scale as `tornado.ioloop.IOLoop.time`, normally `time.time`), or a
`datetime.timedelta` object for a deadline relative to the
current time.
"""
future = Future()
try:
self.put_nowait(item)
except QueueFull:
self._putters.append((item, future))
_set_timeout(future, timeout)
else:
future.set_result(None)
return future
def put_nowait(self, item):
"""Put an item into the queue without blocking.
If no free slot is immediately available, raise `QueueFull`.
"""
self._consume_expired()
if self._getters:
assert self.empty(), "queue non-empty, why are getters waiting?"
getter = self._getters.popleft()
self.__put_internal(item)
future_set_result_unless_cancelled(getter, self._get())
elif self.full():
raise QueueFull
else:
self.__put_internal(item)
def get(self, timeout=None):
"""Remove and return an item from the queue.
Returns a Future which resolves once an item is available, or raises
`tornado.util.TimeoutError` after a timeout.
``timeout`` may be a number denoting a time (on the same
scale as `tornado.ioloop.IOLoop.time`, normally `time.time`), or a
`datetime.timedelta` object for a deadline relative to the
current time.
"""
future = Future()
try:
future.set_result(self.get_nowait())
except QueueEmpty:
self._getters.append(future)
_set_timeout(future, timeout)
return future
def get_nowait(self):
"""Remove and return an item from the queue without blocking.
Return an item if one is immediately available, else raise
`QueueEmpty`.
"""
self._consume_expired()
if self._putters:
assert self.full(), "queue not full, why are putters waiting?"
item, putter = self._putters.popleft()
self.__put_internal(item)
future_set_result_unless_cancelled(putter, None)
return self._get()
elif self.qsize():
return self._get()
else:
raise QueueEmpty
def task_done(self):
"""Indicate that a formerly enqueued task is complete.
Used by queue consumers. For each `.get` used to fetch a task, a
subsequent call to `.task_done` tells the queue that the processing
on the task is complete.
If a `.join` is blocking, it resumes when all items have been
processed; that is, when every `.put` is matched by a `.task_done`.
Raises `ValueError` if called more times than `.put`.
"""
if self._unfinished_tasks <= 0:
raise ValueError('task_done() called too many times')
self._unfinished_tasks -= 1
if self._unfinished_tasks == 0:
self._finished.set()
def join(self, timeout=None):
"""Block until all items in the queue are processed.
Returns a Future, which raises `tornado.util.TimeoutError` after a
timeout.
"""
return self._finished.wait(timeout)
def __aiter__(self):
return _QueueIterator(self)
# These three are overridable in subclasses.
def _init(self):
self._queue = collections.deque()
def _get(self):
return self._queue.popleft()
def _put(self, item):
self._queue.append(item)
# End of the overridable methods.
def __put_internal(self, item):
self._unfinished_tasks += 1
self._finished.clear()
self._put(item)
def _consume_expired(self):
# Remove timed-out waiters.
while self._putters and self._putters[0][1].done():
self._putters.popleft()
while self._getters and self._getters[0].done():
self._getters.popleft()
def __repr__(self):
return '<%s at %s %s>' % (
type(self).__name__, hex(id(self)), self._format())
def __str__(self):
return '<%s %s>' % (type(self).__name__, self._format())
def _format(self):
result = 'maxsize=%r' % (self.maxsize, )
if getattr(self, '_queue', None):
result += ' queue=%r' % self._queue
if self._getters:
result += ' getters[%s]' % len(self._getters)
if self._putters:
result += ' putters[%s]' % len(self._putters)
if self._unfinished_tasks:
result += ' tasks=%s' % self._unfinished_tasks
return result
class PriorityQueue(Queue):
"""A `.Queue` that retrieves entries in priority order, lowest first.
Entries are typically tuples like ``(priority number, data)``.
.. testcode::
from tornado.queues import PriorityQueue
q = PriorityQueue()
q.put((1, 'medium-priority item'))
q.put((0, 'high-priority item'))
q.put((10, 'low-priority item'))
print(q.get_nowait())
print(q.get_nowait())
print(q.get_nowait())
.. testoutput::
(0, 'high-priority item')
(1, 'medium-priority item')
(10, 'low-priority item')
"""
def _init(self):
self._queue = []
def _put(self, item):
heapq.heappush(self._queue, item)
def _get(self):
return heapq.heappop(self._queue)
class LifoQueue(Queue):
"""A `.Queue` that retrieves the most recently put items first.
.. testcode::
from tornado.queues import LifoQueue
q = LifoQueue()
q.put(3)
q.put(2)
q.put(1)
print(q.get_nowait())
print(q.get_nowait())
print(q.get_nowait())
.. testoutput::
1
2
3
"""
def _init(self):
self._queue = []
def _put(self, item):
self._queue.append(item)
def _get(self):
return self._queue.pop()