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b/src/mediaserver/cdplugins/uprcl/rwlock.py |
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# Python Cookbook by David Ascher, Alex Martelli. Credit: Sami Hangaslammi
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import threading
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class ReadWriteLock:
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""" A lock object that allows many simultaneous "read locks", but
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only one "write lock." """
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def __init__(self):
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self._read_ready = threading.Condition(threading.Lock( ))
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self._readers = 0
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def acquire_read(self):
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""" Acquire a read lock. Blocks only if a thread has
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acquired the write lock. """
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self._read_ready.acquire( )
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try:
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self._readers += 1
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finally:
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self._read_ready.release( )
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def release_read(self):
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""" Release a read lock. """
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self._read_ready.acquire( )
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try:
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self._readers -= 1
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if not self._readers:
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self._read_ready.notifyAll( )
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finally:
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self._read_ready.release( )
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def acquire_write(self):
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""" Acquire a write lock. Blocks until there are no
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acquired read or write locks. """
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self._read_ready.acquire( )
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while self._readers > 0:
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self._read_ready.wait( )
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def release_write(self):
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""" Release a write lock. """
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self._read_ready.release( )
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