453 lines
16 KiB
Python
453 lines
16 KiB
Python
# Copyright (c) 2009 Denis Bilenko, denis.bilenko at gmail com
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# Copyright (c) 2010 Eventlet Contributors (see AUTHORS)
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# and licensed under the MIT license:
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#
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# Permission is hereby granted, free of charge, to any person obtaining a copy
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# of this software and associated documentation files (the "Software"), to deal
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# in the Software without restriction, including without limitation the rights
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# to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
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# copies of the Software, and to permit persons to whom the Software is
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# furnished to do so, subject to the following conditions:
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#
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# The above copyright notice and this permission notice shall be included in
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# all copies or substantial portions of the Software.
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#
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# THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
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# IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
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# FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
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# AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
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# LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
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# OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
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# THE SOFTWARE.
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"""Synchronized queues.
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The :mod:`eventlet.queue` module implements multi-producer, multi-consumer
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queues that work across greenlets, with the API similar to the classes found in
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the standard :mod:`Queue` and :class:`multiprocessing <multiprocessing.Queue>`
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modules.
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A major difference is that queues in this module operate as channels when
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initialized with *maxsize* of zero. In such case, both :meth:`Queue.empty`
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and :meth:`Queue.full` return ``True`` and :meth:`Queue.put` always blocks until
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a call to :meth:`Queue.get` retrieves the item.
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An interesting difference, made possible because of greenthreads, is
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that :meth:`Queue.qsize`, :meth:`Queue.empty`, and :meth:`Queue.full` *can* be
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used as indicators of whether the subsequent :meth:`Queue.get`
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or :meth:`Queue.put` will not block. The new methods :meth:`Queue.getting`
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and :meth:`Queue.putting` report on the number of greenthreads blocking
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in :meth:`put <Queue.put>` or :meth:`get <Queue.get>` respectively.
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"""
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import sys
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import heapq
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import collections
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import traceback
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from Queue import Full, Empty
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_NONE = object()
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from eventlet.hubs import get_hub
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from eventlet.greenthread import getcurrent
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from eventlet.event import Event
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from eventlet.timeout import Timeout
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__all__ = ['Queue', 'PriorityQueue', 'LifoQueue', 'LightQueue', 'Full', 'Empty']
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class Waiter(object):
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"""A low level synchronization class.
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Wrapper around greenlet's ``switch()`` and ``throw()`` calls that makes them safe:
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* switching will occur only if the waiting greenlet is executing :meth:`wait`
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method currently. Otherwise, :meth:`switch` and :meth:`throw` are no-ops.
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* any error raised in the greenlet is handled inside :meth:`switch` and :meth:`throw`
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The :meth:`switch` and :meth:`throw` methods must only be called from the :class:`Hub` greenlet.
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The :meth:`wait` method must be called from a greenlet other than :class:`Hub`.
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"""
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__slots__ = ['greenlet']
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def __init__(self):
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self.greenlet = None
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def __repr__(self):
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if self.waiting:
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waiting = ' waiting'
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else:
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waiting = ''
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return '<%s at %s%s greenlet=%r>' % (type(self).__name__, hex(id(self)), waiting, self.greenlet)
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def __str__(self):
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"""
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>>> print Waiter()
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<Waiter greenlet=None>
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"""
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if self.waiting:
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waiting = ' waiting'
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else:
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waiting = ''
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return '<%s%s greenlet=%s>' % (type(self).__name__, waiting, self.greenlet)
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def __nonzero__(self):
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return self.greenlet is not None
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@property
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def waiting(self):
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return self.greenlet is not None
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def switch(self, value=None):
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"""Wake up the greenlet that is calling wait() currently (if there is one).
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Can only be called from Hub's greenlet.
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"""
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assert getcurrent() is get_hub().greenlet, "Can only use Waiter.switch method from the mainloop"
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if self.greenlet is not None:
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try:
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self.greenlet.switch(value)
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except:
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traceback.print_exc()
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def throw(self, *throw_args):
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"""Make greenlet calling wait() wake up (if there is a wait()).
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Can only be called from Hub's greenlet.
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"""
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assert getcurrent() is get_hub().greenlet, "Can only use Waiter.switch method from the mainloop"
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if self.greenlet is not None:
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try:
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self.greenlet.throw(*throw_args)
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except:
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traceback.print_exc()
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# XXX should be renamed to get() ? and the whole class is called Receiver?
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def wait(self):
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"""Wait until switch() or throw() is called.
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"""
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assert self.greenlet is None, 'This Waiter is already used by %r' % (self.greenlet, )
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self.greenlet = getcurrent()
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try:
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return get_hub().switch()
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finally:
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self.greenlet = None
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class LightQueue(object):
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"""
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This is a variant of Queue that behaves mostly like the standard
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:class:`Queue`. It differs by not supporting the
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:meth:`task_done <Queue.task_done>` or :meth:`join <Queue.join>` methods,
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and is a little faster for not having that overhead.
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"""
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def __init__(self, maxsize=None):
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if maxsize < 0:
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self.maxsize = None
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else:
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self.maxsize = maxsize
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self.getters = set()
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self.putters = set()
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self._event_unlock = None
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self._init(maxsize)
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# QQQ make maxsize into a property with setter that schedules unlock if necessary
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def _init(self, maxsize):
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self.queue = collections.deque()
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def _get(self):
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return self.queue.popleft()
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def _put(self, item):
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self.queue.append(item)
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def __repr__(self):
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return '<%s at %s %s>' % (type(self).__name__, hex(id(self)), self._format())
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def __str__(self):
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return '<%s %s>' % (type(self).__name__, self._format())
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def _format(self):
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result = 'maxsize=%r' % (self.maxsize, )
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if getattr(self, 'queue', None):
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result += ' queue=%r' % self.queue
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if self.getters:
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result += ' getters[%s]' % len(self.getters)
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if self.putters:
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result += ' putters[%s]' % len(self.putters)
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if self._event_unlock is not None:
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result += ' unlocking'
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return result
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def qsize(self):
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"""Return the size of the queue."""
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return len(self.queue)
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def resize(self, size):
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"""Resizes the queue's maximum size.
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If the size is increased, and there are putters waiting, they may be woken up."""
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if size > self.maxsize:
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# Maybe wake some stuff up
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self._schedule_unlock()
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self.maxsize = size
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def putting(self):
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"""Returns the number of greenthreads that are blocked waiting to put
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items into the queue."""
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return len(self.putters)
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def getting(self):
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"""Returns the number of greenthreads that are blocked waiting on an
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empty queue."""
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return len(self.getters)
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def empty(self):
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"""Return ``True`` if the queue is empty, ``False`` otherwise."""
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return not self.qsize()
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def full(self):
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"""Return ``True`` if the queue is full, ``False`` otherwise.
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``Queue(None)`` is never full.
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"""
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return self.qsize() >= self.maxsize
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def put(self, item, block=True, timeout=None):
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"""Put an item into the queue.
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If optional arg *block* is true and *timeout* is ``None`` (the default),
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block if necessary until a free slot is available. If *timeout* is
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a positive number, it blocks at most *timeout* seconds and raises
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the :class:`Full` exception if no free slot was available within that time.
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Otherwise (*block* is false), put an item on the queue if a free slot
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is immediately available, else raise the :class:`Full` exception (*timeout*
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is ignored in that case).
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"""
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if self.maxsize is None or self.qsize() < self.maxsize:
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# there's a free slot, put an item right away
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self._put(item)
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if self.getters:
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self._schedule_unlock()
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elif not block and get_hub().greenlet is getcurrent():
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# we're in the mainloop, so we cannot wait; we can switch() to other greenlets though
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# find a getter and deliver an item to it
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while self.getters:
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getter = self.getters.pop()
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if getter:
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self._put(item)
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item = self._get()
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getter.switch(item)
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return
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raise Full
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elif block:
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waiter = ItemWaiter(item)
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self.putters.add(waiter)
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timeout = Timeout(timeout, Full)
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try:
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if self.getters:
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self._schedule_unlock()
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result = waiter.wait()
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assert result is waiter, "Invalid switch into Queue.put: %r" % (result, )
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if waiter.item is not _NONE:
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self._put(item)
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finally:
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timeout.cancel()
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self.putters.discard(waiter)
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else:
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raise Full
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def put_nowait(self, item):
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"""Put an item into the queue without blocking.
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Only enqueue the item if a free slot is immediately available.
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Otherwise raise the :class:`Full` exception.
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"""
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self.put(item, False)
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def get(self, block=True, timeout=None):
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"""Remove and return an item from the queue.
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If optional args *block* is true and *timeout* is ``None`` (the default),
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block if necessary until an item is available. If *timeout* is a positive number,
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it blocks at most *timeout* seconds and raises the :class:`Empty` exception
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if no item was available within that time. Otherwise (*block* is false), return
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an item if one is immediately available, else raise the :class:`Empty` exception
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(*timeout* is ignored in that case).
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"""
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if self.qsize():
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if self.putters:
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self._schedule_unlock()
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return self._get()
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elif not block and get_hub().greenlet is getcurrent():
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# special case to make get_nowait() runnable in the mainloop greenlet
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# there are no items in the queue; try to fix the situation by unlocking putters
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while self.putters:
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putter = self.putters.pop()
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if putter:
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putter.switch(putter)
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if self.qsize():
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return self._get()
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raise Empty
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elif block:
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waiter = Waiter()
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timeout = Timeout(timeout, Empty)
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try:
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self.getters.add(waiter)
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if self.putters:
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self._schedule_unlock()
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return waiter.wait()
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finally:
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self.getters.discard(waiter)
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timeout.cancel()
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else:
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raise Empty
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def get_nowait(self):
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"""Remove and return an item from the queue without blocking.
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Only get an item if one is immediately available. Otherwise
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raise the :class:`Empty` exception.
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"""
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return self.get(False)
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def _unlock(self):
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try:
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while True:
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if self.qsize() and self.getters:
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getter = self.getters.pop()
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if getter:
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try:
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item = self._get()
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except:
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getter.throw(*sys.exc_info())
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else:
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getter.switch(item)
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elif self.putters and self.getters:
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putter = self.putters.pop()
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if putter:
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getter = self.getters.pop()
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if getter:
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item = putter.item
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putter.item = _NONE # this makes greenlet calling put() not to call _put() again
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self._put(item)
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item = self._get()
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getter.switch(item)
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putter.switch(putter)
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else:
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self.putters.add(putter)
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elif self.putters and (self.getters or self.qsize() < self.maxsize):
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putter = self.putters.pop()
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putter.switch(putter)
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else:
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break
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finally:
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self._event_unlock = None # QQQ maybe it's possible to obtain this info from libevent?
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# i.e. whether this event is pending _OR_ currently executing
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# testcase: 2 greenlets: while True: q.put(q.get()) - nothing else has a change to execute
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# to avoid this, schedule unlock with timer(0, ...) once in a while
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def _schedule_unlock(self):
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if self._event_unlock is None:
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self._event_unlock = get_hub().schedule_call_global(0, self._unlock)
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class ItemWaiter(Waiter):
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__slots__ = ['item']
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def __init__(self, item):
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Waiter.__init__(self)
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self.item = item
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class Queue(LightQueue):
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'''Create a queue object with a given maximum size.
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If *maxsize* is less than zero or ``None``, the queue size is infinite.
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``Queue(0)`` is a channel, that is, its :meth:`put` method always blocks
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until the item is delivered. (This is unlike the standard :class:`Queue`,
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where 0 means infinite size).
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In all other respects, this Queue class resembled the standard library,
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:class:`Queue`.
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'''
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def __init__(self, maxsize=None):
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LightQueue.__init__(self, maxsize)
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self.unfinished_tasks = 0
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self._cond = Event()
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def _format(self):
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result = LightQueue._format(self)
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if self.unfinished_tasks:
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result += ' tasks=%s _cond=%s' % (self.unfinished_tasks, self._cond)
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return result
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def _put(self, item):
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LightQueue._put(self, item)
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self._put_bookkeeping()
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def _put_bookkeeping(self):
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self.unfinished_tasks += 1
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if self._cond.ready():
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self._cond.reset()
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def task_done(self):
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'''Indicate that a formerly enqueued task is complete. Used by queue consumer threads.
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For each :meth:`get <Queue.get>` used to fetch a task, a subsequent call to :meth:`task_done` tells the queue
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that the processing on the task is complete.
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If a :meth:`join` is currently blocking, it will resume when all items have been processed
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(meaning that a :meth:`task_done` call was received for every item that had been
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:meth:`put <Queue.put>` into the queue).
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Raises a :exc:`ValueError` if called more times than there were items placed in the queue.
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'''
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if self.unfinished_tasks <= 0:
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raise ValueError('task_done() called too many times')
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self.unfinished_tasks -= 1
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if self.unfinished_tasks == 0:
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self._cond.send(None)
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def join(self):
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'''Block until all items in the queue have been gotten and processed.
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The count of unfinished tasks goes up whenever an item is added to the queue.
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The count goes down whenever a consumer thread calls :meth:`task_done` to indicate
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that the item was retrieved and all work on it is complete. When the count of
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unfinished tasks drops to zero, :meth:`join` unblocks.
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'''
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self._cond.wait()
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class PriorityQueue(Queue):
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'''A subclass of :class:`Queue` that retrieves entries in priority order (lowest first).
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Entries are typically tuples of the form: ``(priority number, data)``.
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'''
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def _init(self, maxsize):
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self.queue = []
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def _put(self, item, heappush=heapq.heappush):
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heappush(self.queue, item)
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self._put_bookkeeping()
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def _get(self, heappop=heapq.heappop):
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return heappop(self.queue)
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class LifoQueue(Queue):
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'''A subclass of :class:`Queue` that retrieves most recently added entries first.'''
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def _init(self, maxsize):
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self.queue = []
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def _put(self, item):
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self.queue.append(item)
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self._put_bookkeeping()
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def _get(self):
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return self.queue.pop()
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