170 lines
5.9 KiB
Python
170 lines
5.9 KiB
Python
"""A multi-producer, multi-consumer queue."""
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from time import time as _time
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from collections import deque
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__all__ = ['Empty', 'Full', 'Queue']
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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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def __init__(self, maxsize=0):
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"""Initialize 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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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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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 two 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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def qsize(self):
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"""Return the approximate size of the queue (not reliable!)."""
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self.mutex.acquire()
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n = self._qsize()
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self.mutex.release()
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return n
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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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self.mutex.acquire()
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n = self._empty()
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self.mutex.release()
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return n
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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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self.mutex.acquire()
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n = self._full()
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self.mutex.release()
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return n
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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 positive 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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self.not_full.acquire()
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try:
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if not block:
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if self._full():
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raise Full
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elif timeout is None:
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while self._full():
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self.not_full.wait()
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else:
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if timeout < 0:
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raise ValueError("'timeout' must be a positive number")
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endtime = _time() + timeout
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while self._full():
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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.not_empty.notify()
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finally:
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self.not_full.release()
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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, 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
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a positive 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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self.not_empty.acquire()
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try:
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if not block:
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if self._empty():
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raise Empty
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elif timeout is None:
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while self._empty():
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self.not_empty.wait()
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else:
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if timeout < 0:
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raise ValueError("'timeout' must be a positive number")
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endtime = _time() + timeout
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while self._empty():
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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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finally:
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self.not_empty.release()
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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(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.maxsize = 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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# Check whether the queue is empty
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def _empty(self):
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return not self.queue
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# Check whether the queue is full
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def _full(self):
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return self.maxsize > 0 and len(self.queue) == self.maxsize
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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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