cpython/Lib/dos-8x3/queue.py

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# A multi-producer, multi-consumer queue.
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# define this exception to be compatible with Python 1.5's class
# exceptions, but also when -X option is used.
try:
class Empty(Exception):
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pass
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class Full(Exception):
pass
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except TypeError:
# string based exceptions
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# exception raised by get(block=0)/get_nowait()
Empty = 'Queue.Empty'
# exception raised by put(block=0)/put_nowait()
Full = 'Queue.Full'
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.
"""
import thread
self._init(maxsize)
self.mutex = thread.allocate_lock()
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
necessary until a free slot is available. Otherwise (block
is 0), put an item on the queue if a free slot is immediately
available, else raise the Full exception.
"""
if block:
self.fsema.acquire()
elif not self.fsema.acquire(0):
raise Full
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self.mutex.acquire()
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was_empty = self._empty()
self._put(item)
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()
self.mutex.release()
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def put_nowait(self, item):
"""Put an item into the queue without blocking.
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Only enqueue the item if a free slot is immediately available.
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):
"""Remove and return an item from the queue.
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If optional arg 'block' is 1 (the default), block if
necessary until an item is available. Otherwise (block is 0),
return an item if one is immediately available, else raise the
Empty exception.
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"""
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if block:
self.esema.acquire()
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()
item = self._get()
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()
self.mutex.release()
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return item
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def get_nowait(self):
"""Remove and return an item from the queue without blocking.
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Only get an item if one is immediately available. Otherwise
raise the Empty exception.
"""
return self.get(0)
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# Override these methods to implement other queue organizations
# (e.g. stack or priority queue).
# These will only be called with appropriate locks held
# Initialize the queue representation
def _init(self, maxsize):
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self.maxsize = maxsize
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
def _empty(self):
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return not self.queue
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# Check whether the queue is full
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
def _put(self, item):
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self.queue.append(item)
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# Get an item from the queue
def _get(self):
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item = self.queue[0]
del self.queue[0]
return item