247 lines
8.6 KiB
Python
247 lines
8.6 KiB
Python
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'''A multi-producer, multi-consumer queue.'''
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try:
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import threading
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except ImportError:
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import dummy_threading as threading
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from collections import deque
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from heapq import heappush, heappop
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from time import monotonic as time
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__all__ = ['Empty', 'Full', 'Queue', 'PriorityQueue', 'LifoQueue']
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class Empty(Exception):
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'Exception raised by Queue.get(block=0)/get_nowait().'
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pass
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class Full(Exception):
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'Exception raised by Queue.put(block=0)/put_nowait().'
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pass
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class Queue:
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'''Create a queue object with a given maximum size.
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If maxsize is <= 0, the queue size is infinite.
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'''
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def __init__(self, maxsize=0):
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self.maxsize = maxsize
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self._init(maxsize)
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# mutex must be held whenever the queue is mutating. All methods
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# that acquire mutex must release it before returning. mutex
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# is shared between the three conditions, so acquiring and
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# releasing the conditions also acquires and releases mutex.
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self.mutex = threading.Lock()
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# Notify not_empty whenever an item is added to the queue; a
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# thread waiting to get is notified then.
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self.not_empty = threading.Condition(self.mutex)
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# Notify not_full whenever an item is removed from the queue;
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# a thread waiting to put is notified then.
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self.not_full = threading.Condition(self.mutex)
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# Notify all_tasks_done whenever the number of unfinished tasks
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# drops to zero; thread waiting to join() is notified to resume
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self.all_tasks_done = threading.Condition(self.mutex)
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self.unfinished_tasks = 0
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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 consumer threads. 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
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have been processed (meaning that a task_done() call was received
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for every item that had been put() into the queue).
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Raises a ValueError if called more times than there were items
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placed in the queue.
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'''
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with self.all_tasks_done:
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unfinished = self.unfinished_tasks - 1
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if unfinished <= 0:
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if unfinished < 0:
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raise ValueError('task_done() called too many times')
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self.all_tasks_done.notify_all()
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self.unfinished_tasks = unfinished
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def join(self):
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'''Blocks 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 thread calls task_done()
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to indicate 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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with self.all_tasks_done:
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while self.unfinished_tasks:
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self.all_tasks_done.wait()
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def qsize(self):
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'''Return the approximate size of the queue (not reliable!).'''
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with self.mutex:
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return self._qsize()
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def empty(self):
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'''Return True if the queue is empty, False otherwise (not reliable!).
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This method is likely to be removed at some point. Use qsize() == 0
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as a direct substitute, but be aware that either approach risks a race
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condition where a queue can grow before the result of empty() or
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qsize() can be used.
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To create code that needs to wait for all queued tasks to be
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completed, the preferred technique is to use the join() method.
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'''
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with self.mutex:
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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 (not reliable!).
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This method is likely to be removed at some point. Use qsize() >= n
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as a direct substitute, but be aware that either approach risks a race
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condition where a queue can shrink before the result of full() or
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qsize() can be used.
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'''
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with self.mutex:
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return 0 < self.maxsize <= self._qsize()
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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 args '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 non-negative number, it blocks at most 'timeout' seconds and raises
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the 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 Full exception ('timeout'
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is ignored in that case).
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'''
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with self.not_full:
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if self.maxsize > 0:
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if not block:
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if self._qsize() >= self.maxsize:
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raise Full
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elif timeout is None:
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while self._qsize() >= self.maxsize:
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self.not_full.wait()
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elif timeout < 0:
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raise ValueError("'timeout' must be a non-negative number")
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else:
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endtime = time() + timeout
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while self._qsize() >= self.maxsize:
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remaining = endtime - time()
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if remaining <= 0.0:
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raise Full
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self.not_full.wait(remaining)
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self._put(item)
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self.unfinished_tasks += 1
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self.not_empty.notify()
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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
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a non-negative number, it blocks at most 'timeout' seconds and raises
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the Empty exception if no item was available within that time.
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Otherwise ('block' is false), return an item if one is immediately
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available, else raise the Empty exception ('timeout' is ignored
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in that case).
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'''
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with self.not_empty:
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if not block:
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if not self._qsize():
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raise Empty
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elif timeout is None:
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while not self._qsize():
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self.not_empty.wait()
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elif timeout < 0:
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raise ValueError("'timeout' must be a non-negative number")
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else:
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endtime = time() + timeout
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while not self._qsize():
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remaining = endtime - time()
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if remaining <= 0.0:
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raise Empty
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self.not_empty.wait(remaining)
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item = self._get()
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self.not_full.notify()
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return 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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Only enqueue the item if a free slot is immediately available.
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Otherwise raise the Full exception.
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'''
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return self.put(item, block=False)
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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 Empty exception.
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'''
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return self.get(block=False)
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# Override these methods to implement other queue organizations
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# (e.g. stack or priority queue).
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# These will only be called with appropriate locks held
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# Initialize the queue representation
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def _init(self, maxsize):
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self.queue = deque()
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def _qsize(self):
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return len(self.queue)
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# Put a new item in the queue
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def _put(self, item):
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self.queue.append(item)
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# Get an item from the queue
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def _get(self):
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return self.queue.popleft()
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class PriorityQueue(Queue):
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'''Variant of Queue that retrieves open 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 _qsize(self):
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return len(self.queue)
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def _put(self, item):
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heappush(self.queue, item)
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def _get(self):
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return heappop(self.queue)
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class LifoQueue(Queue):
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'''Variant 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 _qsize(self):
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return len(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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