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import multiprocessing |
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from multiprocessing.queues import Queue as MPQueue |
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from six.moves import queue as BaseQueue |
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Empty = BaseQueue.Empty |
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Full = BaseQueue.Full |
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# The SharedCounter and Queue classes come from: |
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# https://github.com/vterron/lemon/commit/9ca6b4b |
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class SharedCounter(object): |
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""" A synchronized shared counter. |
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The locking done by multiprocessing.Value ensures that only a single |
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process or thread may read or write the in-memory ctypes object. However, |
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in order to do n += 1, Python performs a read followed by a write, so a |
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second process may read the old value before the new one is written by the |
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first process. The solution is to use a multiprocessing.Lock to guarantee |
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the atomicity of the modifications to Value. |
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This class comes almost entirely from Eli Bendersky's blog: |
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http://eli.thegreenplace.net/2012/01/04/shared-counter-with-pythons-multiprocessing/ |
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""" |
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def __init__(self, n=0): |
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self.count = multiprocessing.Value('i', n) |
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def increment(self, n=1): |
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""" Increment the counter by n (default = 1) """ |
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with self.count.get_lock(): |
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self.count.value += n |
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@property |
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def value(self): |
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""" Return the value of the counter """ |
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return self.count.value |
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class Queue(BaseQueue.Queue, object): |
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""" A portable implementation of multiprocessing.Queue. |
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Because of multithreading / multiprocessing semantics, Queue.qsize() may |
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raise the NotImplementedError exception on Unix platforms like Mac OS X |
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where sem_getvalue() is not implemented. This subclass addresses this |
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problem by using a synchronized shared counter (initialized to zero) and |
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increasing / decreasing its value every time the put() and get() methods |
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are called, respectively. This not only prevents NotImplementedError from |
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being raised, but also allows us to implement a reliable version of both |
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qsize() and empty(). |
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""" |
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def __init__(self, *args, **kwargs): |
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super(Queue, self).__init__(*args, **kwargs) |
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self.size = SharedCounter(0) |
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def _put(self, *args, **kwargs): |
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self.size.increment(1) |
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super(Queue, self).put(*args, **kwargs) |
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def _get(self, *args, **kwargs): |
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v = super(Queue, self).get(*args, **kwargs) |
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self.size.increment(-1) |
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return v |
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def _qsize(self): |
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""" Reliable implementation of multiprocessing.Queue.qsize() """ |
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return self.size.value |
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class MultiProcessingQueue(MPQueue, object): |
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def __init__(self, *args, **kwargs): |
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super(MultiProcessingQueue, self).__init__(*args, **kwargs) |
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self.size = SharedCounter(0) |
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def _put(self, *args, **kwargs): |
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self.size.increment(1) |
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super(MultiProcessingQueue, self).put(*args, **kwargs) |
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def _get(self, *args, **kwargs): |
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v = super(MultiProcessingQueue, self).get(*args, **kwargs) |
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self.size.increment(-1) |
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return v |
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def _qsize(self): |
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""" Reliable implementation of multiprocessing.Queue.qsize() """ |
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return self.size.value |
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def get_multiprocessing_queue(maxsize=0): |
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if hasattr(multiprocessing, 'get_context'): # python 3.4 |
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return MultiProcessingQueue(maxsize, |
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ctx=multiprocessing.get_context()) |
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else: |
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return MultiProcessingQueue(maxsize=maxsize) |
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binux /
pyspider
