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