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140 lines
4 KiB
Python
140 lines
4 KiB
Python
# A multi-producer, multi-consumer queue.
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# define this exception to be compatible with Python 1.5's class
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# exceptions, but also when -X option is used.
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try:
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class Empty(Exception):
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pass
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except TypeError:
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# string based exceptions
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Empty = 'Queue.Empty' # Exception raised by get_nowait()
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class Queue:
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def __init__(self, maxsize):
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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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"""Returns 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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"""Returns 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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"""Returns 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):
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"""Put an item into the queue.
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If the queue is full, block until a free slot is avaiable.
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"""
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self.fsema.acquire()
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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 get(self):
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"""Gets and returns an item from the queue.
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This method blocks if necessary until an item is available.
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"""
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self.esema.acquire()
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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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# Get an item from the queue if one is immediately available,
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# raise Empty if the queue is empty or temporarily unavailable
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def get_nowait(self):
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"""Gets and returns an item from the queue.
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Only gets an item if one is immediately available, Otherwise
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this raises the Empty exception if the queue is empty or
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temporarily unavailable.
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"""
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locked = self.esema.acquire(0)
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self.mutex.acquire()
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if self._empty():
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# The queue is empty -- we can't have esema
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self.mutex.release()
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raise Empty
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if not locked:
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locked = self.esema.acquire(0)
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if not locked:
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# Somebody else has esema
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# but we have mutex --
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# go out of their way
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self.mutex.release()
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raise Empty
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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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# XXX Need to define put_nowait() as well.
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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 wheter 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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