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324 lines
10 KiB
Python
324 lines
10 KiB
Python
"""Queues"""
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__all__ = ['Queue', 'PriorityQueue', 'LifoQueue', 'QueueFull', 'QueueEmpty']
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import collections
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import heapq
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from . import compat
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from . import events
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from . import futures
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from . import locks
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from .coroutines import coroutine
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class QueueEmpty(Exception):
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"""Exception raised when Queue.get_nowait() is called on a Queue object
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which is empty.
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"""
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pass
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class QueueFull(Exception):
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"""Exception raised when the Queue.put_nowait() method is called on a Queue
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object which is full.
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"""
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pass
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class Queue:
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"""A queue, useful for coordinating producer and consumer coroutines.
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If maxsize is less than or equal to zero, the queue size is infinite. If it
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is an integer greater than 0, then "yield from put()" will block when the
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queue reaches maxsize, until an item is removed by get().
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Unlike the standard library Queue, you can reliably know this Queue's size
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with qsize(), since your single-threaded asyncio application won't be
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interrupted between calling qsize() and doing an operation on the Queue.
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"""
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def __init__(self, maxsize=0, *, loop=None):
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if loop is None:
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self._loop = events.get_event_loop()
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else:
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self._loop = loop
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self._maxsize = maxsize
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# Futures.
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self._getters = collections.deque()
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# Futures
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self._putters = collections.deque()
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self._unfinished_tasks = 0
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self._finished = locks.Event(loop=self._loop)
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self._finished.set()
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self._init(maxsize)
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# These three are overridable in subclasses.
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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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# End of the overridable methods.
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def __put_internal(self, item):
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self._put(item)
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self._unfinished_tasks += 1
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self._finished.clear()
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def __repr__(self):
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return '<{} at {:#x} {}>'.format(
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type(self).__name__, id(self), self._format())
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def __str__(self):
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return '<{} {}>'.format(type(self).__name__, self._format())
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def _format(self):
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result = 'maxsize={!r}'.format(self._maxsize)
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if getattr(self, '_queue', None):
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result += ' _queue={!r}'.format(list(self._queue))
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if self._getters:
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result += ' _getters[{}]'.format(len(self._getters))
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if self._putters:
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result += ' _putters[{}]'.format(len(self._putters))
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if self._unfinished_tasks:
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result += ' tasks={}'.format(self._unfinished_tasks)
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return result
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def _consume_done_getters(self):
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# Delete waiters at the head of the get() queue who've timed out.
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while self._getters and self._getters[0].done():
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self._getters.popleft()
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def _consume_done_putters(self):
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# Delete waiters at the head of the put() queue who've timed out.
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while self._putters and self._putters[0].done():
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self._putters.popleft()
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def qsize(self):
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"""Number of items in the queue."""
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return len(self._queue)
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@property
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def maxsize(self):
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"""Number of items allowed in the queue."""
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return self._maxsize
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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._queue
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def full(self):
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"""Return True if there are maxsize items in the queue.
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Note: if the Queue was initialized with maxsize=0 (the default),
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then full() is never True.
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"""
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if self._maxsize <= 0:
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return False
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else:
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return self.qsize() >= self._maxsize
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@coroutine
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def put(self, item):
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"""Put an item into the queue.
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Put an item into the queue. If the queue is full, wait until a free
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slot is available before adding item.
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This method is a coroutine.
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"""
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self._consume_done_getters()
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if self._getters:
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assert not self._queue, (
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'queue non-empty, why are getters waiting?')
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getter = self._getters.popleft()
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self.__put_internal(item)
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# getter cannot be cancelled, we just removed done getters
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getter.set_result(self._get())
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elif self._maxsize > 0 and self._maxsize <= self.qsize():
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waiter = futures.Future(loop=self._loop)
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self._putters.append(waiter)
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yield from waiter
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self._put(item)
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else:
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self.__put_internal(item)
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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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If no free slot is immediately available, raise QueueFull.
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"""
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self._consume_done_getters()
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if self._getters:
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assert not self._queue, (
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'queue non-empty, why are getters waiting?')
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getter = self._getters.popleft()
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self.__put_internal(item)
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# getter cannot be cancelled, we just removed done getters
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getter.set_result(self._get())
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elif self._maxsize > 0 and self._maxsize <= self.qsize():
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raise QueueFull
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else:
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self.__put_internal(item)
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@coroutine
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def get(self):
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"""Remove and return an item from the queue.
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If queue is empty, wait until an item is available.
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This method is a coroutine.
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"""
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self._consume_done_putters()
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if self._putters:
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assert self.full(), 'queue not full, why are putters waiting?'
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putter = self._putters.popleft()
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# When a getter runs and frees up a slot so this putter can
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# run, we need to defer the put for a tick to ensure that
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# getters and putters alternate perfectly. See
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# ChannelTest.test_wait.
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self._loop.call_soon(putter._set_result_unless_cancelled, None)
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return self._get()
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elif self.qsize():
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return self._get()
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else:
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waiter = futures.Future(loop=self._loop)
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self._getters.append(waiter)
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try:
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return (yield from waiter)
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except futures.CancelledError:
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# if we get CancelledError, it means someone cancelled this
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# get() coroutine. But there is a chance that the waiter
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# already is ready and contains an item that has just been
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# removed from the queue. In this case, we need to put the item
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# back into the front of the queue. This get() must either
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# succeed without fault or, if it gets cancelled, it must be as
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# if it never happened.
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if waiter.done():
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self._put_it_back(waiter.result())
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raise
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def _put_it_back(self, item):
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"""
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This is called when we have a waiter to get() an item and this waiter
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gets cancelled. In this case, we put the item back: wake up another
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waiter or put it in the _queue.
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"""
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self._consume_done_getters()
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if self._getters:
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assert not self._queue, (
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'queue non-empty, why are getters waiting?')
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getter = self._getters.popleft()
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self.__put_internal(item)
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# getter cannot be cancelled, we just removed done getters
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getter.set_result(item)
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else:
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self._queue.appendleft(item)
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def get_nowait(self):
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"""Remove and return an item from the queue.
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Return an item if one is immediately available, else raise QueueEmpty.
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"""
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self._consume_done_putters()
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if self._putters:
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assert self.full(), 'queue not full, why are putters waiting?'
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putter = self._putters.popleft()
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# Wake putter on next tick.
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# getter cannot be cancelled, we just removed done putters
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putter.set_result(None)
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return self._get()
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elif self.qsize():
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return self._get()
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else:
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raise QueueEmpty
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def task_done(self):
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"""Indicate that a formerly enqueued task is complete.
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Used by queue consumers. For each get() used to fetch a task,
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a subsequent call to task_done() tells the queue that the processing
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on the task is complete.
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If a join() is currently blocking, it will resume when all items have
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been processed (meaning that a task_done() call was received for every
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item that had been put() into the queue).
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Raises ValueError if called more times than there were items placed in
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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._finished.set()
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@coroutine
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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
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queue. The count goes down whenever a consumer calls task_done() to
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indicate that the item was retrieved and all work on it is complete.
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When the count of unfinished tasks drops to zero, join() unblocks.
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"""
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if self._unfinished_tasks > 0:
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yield from self._finished.wait()
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class PriorityQueue(Queue):
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"""A subclass of Queue; 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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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 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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def _get(self):
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return self._queue.pop()
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if not compat.PY35:
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JoinableQueue = Queue
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"""Deprecated alias for Queue."""
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__all__.append('JoinableQueue')
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