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133 lines
3.8 KiB
Python
133 lines
3.8 KiB
Python
"""A multi-producer, multi-consumer 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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import thread
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self._init(maxsize)
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self.mutex = thread.allocate_lock()
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self.esema = thread.allocate_lock()
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self.esema.acquire()
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self.fsema = thread.allocate_lock()
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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 1 if the queue is empty, 0 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 1 if the queue is full, 0 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=1):
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"""Put an item into the queue.
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If optional arg 'block' is 1 (the default), block if
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necessary until a free slot is available. Otherwise (block
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is 0), put an item on the queue if a free slot is immediately
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available, else raise the Full exception.
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"""
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if block:
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self.fsema.acquire()
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elif not self.fsema.acquire(0):
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raise Full
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self.mutex.acquire()
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was_empty = self._empty()
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self._put(item)
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if was_empty:
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self.esema.release()
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if not self._full():
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self.fsema.release()
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self.mutex.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, 0)
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def get(self, block=1):
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"""Remove and return an item from the queue.
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If optional arg 'block' is 1 (the default), block if
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necessary until an item is available. Otherwise (block is 0),
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return an item if one is immediately available, else raise the
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Empty exception.
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"""
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if block:
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self.esema.acquire()
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elif not self.esema.acquire(0):
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raise Empty
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self.mutex.acquire()
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was_full = self._full()
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item = self._get()
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if was_full:
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self.fsema.release()
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if not self._empty():
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self.esema.release()
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self.mutex.release()
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return item
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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(0)
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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 = []
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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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item = self.queue[0]
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del self.queue[0]
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return item
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