257 lines
6.6 KiB
Python
257 lines
6.6 KiB
Python
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"""Synchronization metaclass.
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This metaclass makes it possible to declare synchronized methods.
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"""
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import thread
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# First we need to define a reentrant lock.
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# This is generally useful and should probably be in a standard Python
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# library module. For now, we in-line it.
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class Lock:
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"""Reentrant lock.
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This is a mutex-like object which can be acquired by the same
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thread more than once. It keeps a reference count of the number
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of times it has been acquired by the same thread. Each acquire()
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call must be matched by a release() call and only the last
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release() call actually releases the lock for acquisition by
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another thread.
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The implementation uses two locks internally:
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__mutex is a short term lock used to protect the instance variables
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__wait is the lock for which other threads wait
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A thread intending to acquire both locks should acquire __wait
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first.
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The implementation uses two other instance variables, protected by
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locking __mutex:
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__tid is the thread ID of the thread that currently has the lock
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__count is the number of times the current thread has acquired it
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When the lock is released, __tid is None and __count is zero.
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"""
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def __init__(self):
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"""Constructor. Initialize all instance variables."""
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self.__mutex = thread.allocate_lock()
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self.__wait = thread.allocate_lock()
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self.__tid = None
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self.__count = 0
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def acquire(self, flag=1):
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"""Acquire the lock.
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If the optional flag argument is false, returns immediately
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when it cannot acquire the __wait lock without blocking (it
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may still block for a little while in order to acquire the
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__mutex lock).
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The return value is only relevant when the flag argument is
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false; it is 1 if the lock is acquired, 0 if not.
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"""
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self.__mutex.acquire()
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try:
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if self.__tid == thread.get_ident():
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self.__count = self.__count + 1
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return 1
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finally:
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self.__mutex.release()
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locked = self.__wait.acquire(flag)
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if not flag and not locked:
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return 0
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try:
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self.__mutex.acquire()
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assert self.__tid == None
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assert self.__count == 0
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self.__tid = thread.get_ident()
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self.__count = 1
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return 1
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finally:
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self.__mutex.release()
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def release(self):
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"""Release the lock.
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If this thread doesn't currently have the lock, an assertion
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error is raised.
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Only allow another thread to acquire the lock when the count
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reaches zero after decrementing it.
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"""
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self.__mutex.acquire()
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try:
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assert self.__tid == thread.get_ident()
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assert self.__count > 0
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self.__count = self.__count - 1
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if self.__count == 0:
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self.__tid = None
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self.__wait.release()
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finally:
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self.__mutex.release()
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def _testLock():
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done = []
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def f2(lock, done=done):
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lock.acquire()
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print "f2 running in thread %d\n" % thread.get_ident(),
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lock.release()
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done.append(1)
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def f1(lock, f2=f2, done=done):
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lock.acquire()
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print "f1 running in thread %d\n" % thread.get_ident(),
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try:
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f2(lock)
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finally:
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lock.release()
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done.append(1)
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lock = Lock()
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lock.acquire()
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f1(lock) # Adds 2 to done
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lock.release()
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lock.acquire()
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thread.start_new_thread(f1, (lock,)) # Adds 2
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thread.start_new_thread(f1, (lock, f1)) # Adds 3
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thread.start_new_thread(f2, (lock,)) # Adds 1
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thread.start_new_thread(f2, (lock,)) # Adds 1
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lock.release()
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import time
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while len(done) < 9:
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print len(done)
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time.sleep(0.001)
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print len(done)
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# Now, the Locking metaclass is a piece of cake.
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# As an example feature, methods whose name begins with exactly one
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# underscore are not synchronized.
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from Meta import MetaClass, MetaHelper, MetaMethodWrapper
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class LockingMethodWrapper(MetaMethodWrapper):
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def __call__(self, *args, **kw):
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if self.__name__[:1] == '_' and self.__name__[1:] != '_':
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return apply(self.func, (self.inst,) + args, kw)
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self.inst.__lock__.acquire()
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try:
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return apply(self.func, (self.inst,) + args, kw)
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finally:
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self.inst.__lock__.release()
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class LockingHelper(MetaHelper):
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__methodwrapper__ = LockingMethodWrapper
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def __helperinit__(self, formalclass):
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MetaHelper.__helperinit__(self, formalclass)
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self.__lock__ = Lock()
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class LockingMetaClass(MetaClass):
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__helper__ = LockingHelper
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Locking = LockingMetaClass('Locking', (), {})
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def _test():
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# For kicks, take away the Locking base class and see it die
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class Buffer(Locking):
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def __init__(self, initialsize):
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assert initialsize > 0
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self.size = initialsize
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self.buffer = [None]*self.size
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self.first = self.last = 0
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def put(self, item):
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# Do we need to grow the buffer?
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if (self.last+1) % self.size != self.first:
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# Insert the new item
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self.buffer[self.last] = item
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self.last = (self.last+1) % self.size
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return
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# Double the buffer size
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# First normalize it so that first==0 and last==size-1
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print "buffer =", self.buffer
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print "first = %d, last = %d, size = %d" % (
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self.first, self.last, self.size)
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if self.first <= self.last:
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temp = self.buffer[self.first:self.last]
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else:
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temp = self.buffer[self.first:] + self.buffer[:self.last]
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print "temp =", temp
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self.buffer = temp + [None]*(self.size+1)
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self.first = 0
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self.last = self.size-1
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self.size = self.size*2
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print "Buffer size doubled to", self.size
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print "new buffer =", self.buffer
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print "first = %d, last = %d, size = %d" % (
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self.first, self.last, self.size)
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self.put(item) # Recursive call to test the locking
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def get(self):
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# Is the buffer empty?
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if self.first == self.last:
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raise EOFError # Avoid defining a new exception
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item = self.buffer[self.first]
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self.first = (self.first+1) % self.size
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return item
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def producer(buffer, wait, n=1000):
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import time
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i = 0
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while i < n:
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print "put", i
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buffer.put(i)
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i = i+1
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print "Producer: done producing", n, "items"
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wait.release()
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def consumer(buffer, wait, n=1000):
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import time
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i = 0
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tout = 0.001
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while i < n:
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try:
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x = buffer.get()
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if x != i:
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raise AssertionError, \
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"get() returned %s, expected %s" % (x, i)
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print "got", i
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i = i+1
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tout = 0.001
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except EOFError:
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time.sleep(tout)
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tout = tout*2
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print "Consumer: done consuming", n, "items"
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wait.release()
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pwait = thread.allocate_lock()
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pwait.acquire()
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cwait = thread.allocate_lock()
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cwait.acquire()
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buffer = Buffer(1)
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n = 1000
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thread.start_new_thread(consumer, (buffer, cwait, n))
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thread.start_new_thread(producer, (buffer, pwait, n))
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pwait.acquire()
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print "Producer done"
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cwait.acquire()
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print "All done"
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print "buffer size ==", len(buffer.buffer)
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if __name__ == '__main__':
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_testLock()
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_test()
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