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Diffstat (limited to 'src/software/openlmi/software/util/singletonmixin.py')
| -rw-r--r-- | src/software/openlmi/software/util/singletonmixin.py | 562 |
1 files changed, 307 insertions, 255 deletions
diff --git a/src/software/openlmi/software/util/singletonmixin.py b/src/software/openlmi/software/util/singletonmixin.py index 8051695..7b26b8b 100644 --- a/src/software/openlmi/software/util/singletonmixin.py +++ b/src/software/openlmi/software/util/singletonmixin.py @@ -1,8 +1,9 @@ +#pylint: disable-all """ A Python Singleton mixin class that makes use of some of the ideas found at http://c2.com/cgi/wiki?PythonSingleton. Just inherit from it and you have a singleton. No code is required in -subclasses to create singleton behavior -- inheritance from +subclasses to create singleton behavior -- inheritance from Singleton is all that is needed. Singleton creation is threadsafe. @@ -11,8 +12,8 @@ USAGE: Just inherit from Singleton. If you need a constructor, include an __init__() method in your class as you usually would. However, -if your class is S, you instantiate the singleton using S.getInstance() -instead of S(). Repeated calls to S.getInstance() return the +if your class is S, you instantiate the singleton using S.get_instance() +instead of S(). Repeated calls to S.get_instance() return the originally-created instance. For example: @@ -21,8 +22,8 @@ class S(Singleton): def __init__(self, a, b=1): pass - -S1 = S.getInstance(1, b=3) + +S1 = S.get_instance(1, b=3) Most of the time, that's all you need to know. However, there are some @@ -30,46 +31,47 @@ other useful behaviors. Read on for a full description: 1) Getting the singleton: - S.getInstance() - -returns the instance of S. If none exists, it is created. + S.get_instance() + +returns the instance of S. If none exists, it is created. 2) The usual idiom to construct an instance by calling the class, i.e. S() - -is disabled for the sake of clarity. -For one thing, the S() syntax means instantiation, but getInstance() +is disabled for the sake of clarity. + +For one thing, the S() syntax means instantiation, but get_instance() usually does not cause instantiation. So the S() syntax would be misleading. -Because of that, if S() were allowed, a programmer who didn't +Because of that, if S() were allowed, a programmer who didn't happen to notice the inheritance from Singleton (or who wasn't fully aware of what a Singleton pattern -does) might think he was creating a new instance, +does) might think he was creating a new instance, which could lead to very unexpected behavior. So, overall, it is felt that it is better to make things clearer by requiring the call of a class method that is defined in -Singleton. An attempt to instantiate via S() will result +Singleton. An attempt to instantiate via S() will result in a SingletonException being raised. 3) Use __S.__init__() for instantiation processing, -since S.getInstance() runs S.__init__(), passing it the args it has received. +since S.get_instance() runs S.__init__(), passing it the args it has received. -If no data needs to be passed in at instantiation time, you don't need S.__init__(). +If no data needs to be passed in at instantiation time, +you don't need S.__init__(). 4) If S.__init__(.) requires parameters, include them ONLY in the -first call to S.getInstance(). If subsequent calls have arguments, +first call to S.get_instance(). If subsequent calls have arguments, a SingletonException is raised by default. If you find it more convenient for subsequent calls to be allowed to -have arguments, but for those argumentsto be ignored, just include +have arguments, but for those argumentsto be ignored, just include 'ignoreSubsequent = True' in your class definition, i.e.: class S(Singleton): - + ignoreSubsequent = True def __init__(self, a, b=1): @@ -77,345 +79,392 @@ have arguments, but for those argumentsto be ignored, just include 5) For testing, it is sometimes convenient for all existing singleton instances to be forgotten, so that new instantiations can occur. For that -reason, a forgetAllSingletons() function is included. Just call +reason, a _forget_all_singletons() function is included. Just call + + _forget_all_singletons() - forgetAllSingletons() - and it is as if no earlier instantiations have occurred. -6) As an implementation detail, classes that inherit +6) As an implementation detail, classes that inherit from Singleton may not have their own __new__ -methods. To make sure this requirement is followed, +methods. To make sure this requirement is followed, an exception is raised if a Singleton subclass includ es __new__. This happens at subclass instantiation time (by means of the MetaSingleton metaclass. -By Gary Robinson, grobinson@flyfi.com. No rights reserved -- +By Gary Robinson, grobinson@flyfi.com. No rights reserved -- placed in the public domain -- which is only reasonable considering how much it owes to other people's code and ideas which are in the -public domain. The idea of using a metaclass came from -a comment on Gary's blog (see -http://www.garyrobinson.net/2004/03/python_singleto.html#comments). +public domain. The idea of using a metaclass came from +a comment on Gary's blog (see +http://www.garyrobinson.net/2004/03/python_singleto.html#comments). Other improvements came from comments and email from other people who saw it online. (See the blog post and comments for further credits.) Not guaranteed to be fit for any particular purpose. Use at your -own risk. +own risk. """ import threading class SingletonException(Exception): + """ + Base exception related to singleton handling. + """ pass -_stSingletons = set() -_lockForSingletons = threading.RLock() -_lockForSingletonCreation = threading.RLock() # Ensure only one instance of each Singleton - # class is created. This is not bound to the - # individual Singleton class since we need to - # ensure that there is only one mutex for each - # Singleton class, which would require having - # a lock when setting up the Singleton class, - # which is what this is anyway. So, when any - # Singleton is created, we lock this lock and - # then we don't need to lock it again for that - # class. - -def _createSingletonInstance(cls, lstArgs, dctKwArgs): - _lockForSingletonCreation.acquire() +_ST_SINGLETONS = set() +_LOCK_FOR_SINGLETONS = threading.RLock() +# Ensure only one instance of each Singleton class is created. This is not +# bound to the _LOCK_FOR_SINGLETON_CREATION = threading.RLock() individual +# Singleton class since we need to ensure that there is only one mutex for each +# Singleton class, which would require having a lock when setting up the +# Singleton class, which is what this is anyway. So, when any Singleton is +# created, we lock this lock and then we don't need to lock it again for that +# class. +_LOCK_FOR_SINGLETON_CREATION = threading.RLock() + +def _create_singleton_instance(cls, lst_args, dct_kw_args): + """ + Creates singleton instance and stores its class in set. + """ + _LOCK_FOR_SINGLETON_CREATION.acquire() try: - if cls._isInstantiated(): # some other thread got here first - return - + if cls._is_instantiated(): # some other thread got here first + return + instance = cls.__new__(cls) try: - instance.__init__(*lstArgs, **dctKwArgs) - except TypeError, e: - if e.message.find('__init__() takes') != -1: - raise SingletonException, 'If the singleton requires __init__ args, supply them on first call to getInstance().' + instance.__init__(*lst_args, **dct_kw_args) + except TypeError, exc: + if '__init__() takes' in exc.message: + raise SingletonException, ( + 'If the singleton requires __init__ args,' + ' supply them on first call to get_instance().') else: raise - cls.cInstance = instance - _addSingleton(cls) + cls.c_instance = instance + _add_singleton(cls) finally: - _lockForSingletonCreation.release() + _LOCK_FOR_SINGLETON_CREATION.release() -def _addSingleton(cls): - _lockForSingletons.acquire() +def _add_singleton(cls): + """ + Adds class to singleton set. + """ + _LOCK_FOR_SINGLETONS.acquire() try: - assert cls not in _stSingletons - _stSingletons.add(cls) + assert cls not in _ST_SINGLETONS + _ST_SINGLETONS.add(cls) finally: - _lockForSingletons.release() + _LOCK_FOR_SINGLETONS.release() -def _removeSingleton(cls): - _lockForSingletons.acquire() +def _remove_singleton(cls): + """ + Removes class from singleton set. + """ + _LOCK_FOR_SINGLETONS.acquire() try: - if cls in _stSingletons: - _stSingletons.remove(cls) + if cls in _ST_SINGLETONS: + _ST_SINGLETONS.remove(cls) finally: - _lockForSingletons.release() - -def forgetAllSingletons(): - '''This is useful in tests, since it is hard to know which singletons need to be cleared to make a test work.''' - _lockForSingletons.acquire() + _LOCK_FOR_SINGLETONS.release() + +def _forget_all_singletons(): + ''' + This is useful in tests, since it is hard to know which singletons need + to be cleared to make a test work. + ''' + _LOCK_FOR_SINGLETONS.acquire() try: - for cls in _stSingletons.copy(): - cls._forgetClassInstanceReferenceForTesting() + for cls in _ST_SINGLETONS.copy(): + cls._forget_class_instance_reference_for_testing() # Might have created some Singletons in the process of tearing down. # Try one more time - there should be a limit to this. - iNumSingletons = len(_stSingletons) - if len(_stSingletons) > 0: - for cls in _stSingletons.copy(): - cls._forgetClassInstanceReferenceForTesting() - iNumSingletons -= 1 - assert iNumSingletons == len(_stSingletons), 'Added a singleton while destroying ' + str(cls) - assert len(_stSingletons) == 0, _stSingletons + i_num_singletons = len(_ST_SINGLETONS) + if len(_ST_SINGLETONS) > 0: + for cls in _ST_SINGLETONS.copy(): + cls._forget_class_instance_reference_for_testing() + i_num_singletons -= 1 + assert i_num_singletons == len(_ST_SINGLETONS), \ + 'Added a singleton while destroying ' + str(cls) + assert len(_ST_SINGLETONS) == 0, _ST_SINGLETONS finally: - _lockForSingletons.release() + _LOCK_FOR_SINGLETONS.release() class MetaSingleton(type): - def __new__(metaclass, strName, tupBases, dct): + """ + Metaclass for Singleton base class. + """ + def __new__(mcs, str_name, tup_bases, dct): if dct.has_key('__new__'): raise SingletonException, 'Can not override __new__ in a Singleton' - return super(MetaSingleton, metaclass).__new__(metaclass, strName, tupBases, dct) - - def __call__(cls, *lstArgs, **dictArgs): - raise SingletonException, 'Singletons may only be instantiated through getInstance()' - + return super(MetaSingleton, mcs).__new__( + mcs, str_name, tup_bases, dct) + + def __call__(cls, *lst_args, **dictArgs): + raise SingletonException, \ + 'Singletons may only be instantiated through get_instance()' + class Singleton(object): + """ + Base class for all singletons. + """ __metaclass__ = MetaSingleton - - def getInstance(cls, *lstArgs, **dctKwArgs): + + def get_instance(cls, *lst_args, **dct_kw_args): """ Call this to instantiate an instance or retrieve the existing instance. If the singleton requires args to be instantiated, include them the first - time you call getInstance. + time you call get_instance. """ - if cls._isInstantiated(): - if (lstArgs or dctKwArgs) and not hasattr(cls, 'ignoreSubsequent'): - raise SingletonException, 'Singleton already instantiated, but getInstance() called with args.' + if cls._is_instantiated(): + if ( (lst_args or dct_kw_args) + and not hasattr(cls, 'ignoreSubsequent')): + raise SingletonException, ( + 'Singleton already instantiated, but get_instance()' + ' called with args.') else: - _createSingletonInstance(cls, lstArgs, dctKwArgs) - - return cls.cInstance - getInstance = classmethod(getInstance) - - def _isInstantiated(cls): - # Don't use hasattr(cls, 'cInstance'), because that screws things up if there is a singleton that - # extends another singleton. hasattr looks in the base class if it doesn't find in subclass. - return 'cInstance' in cls.__dict__ - _isInstantiated = classmethod(_isInstantiated) + _create_singleton_instance(cls, lst_args, dct_kw_args) + + return cls.c_instance #pylint: disable=E1101 + get_instance = classmethod(get_instance) + + def _is_instantiated(cls): + """ + Don't use hasattr(cls, 'c_instance'), because that screws things + up if there is a singleton that extends another singleton. + hasattr looks in the base class if it doesn't find in subclass. + """ + return 'c_instance' in cls.__dict__ + _is_instantiated = classmethod(_is_instantiated) # This can be handy for public use also - isInstantiated = _isInstantiated + isInstantiated = _is_instantiated - def _forgetClassInstanceReferenceForTesting(cls): + def _forget_class_instance_reference_for_testing(cls): """ - This is designed for convenience in testing -- sometimes you + This is designed for convenience in testing -- sometimes you want to get rid of a singleton during test code to see what - happens when you call getInstance() under a new situation. - + happens when you call get_instance() under a new situation. + To really delete the object, all external references to it also need to be deleted. """ try: - if hasattr(cls.cInstance, '_prepareToForgetSingleton'): + if hasattr(cls.c_instance, '_prepare_to_forget_singleton'): # tell instance to release anything it might be holding onto. - cls.cInstance._prepareToForgetSingleton() - del cls.cInstance - _removeSingleton(cls) + cls.c_instance._prepare_to_forget_singleton() + del cls.c_instance + _remove_singleton(cls) except AttributeError: - # run up the chain of base classes until we find the one that has the instance - # and then delete it there - for baseClass in cls.__bases__: - if issubclass(baseClass, Singleton): - baseClass._forgetClassInstanceReferenceForTesting() - _forgetClassInstanceReferenceForTesting = classmethod(_forgetClassInstanceReferenceForTesting) - - -if __name__ == '__main__': + # run up the chain of base classes until we find the one that has + # the instance and then delete it there + for base_class in cls.__bases__: + if issubclass(base_class, Singleton): + base_class._forget_class_instance_reference_for_testing() + _forget_class_instance_reference_for_testing = classmethod( + _forget_class_instance_reference_for_testing) + + +if __name__ == '__main__': import unittest import time - - class singletonmixin_Public_TestCase(unittest.TestCase): - def testReturnsSameObject(self): + + class SingletonMixinPublicTestCase(unittest.TestCase): + """ + TestCase for singleton class. + """ + def testReturnsSameObject(self): #pylint: disable=C0103 """ - Demonstrates normal use -- just call getInstance and it returns a singleton instance + Demonstrates normal use -- just call get_instance and it returns a singleton instance """ - - class A(Singleton): + + class Foo(Singleton): + """Singleton child class.""" def __init__(self): - super(A, self).__init__() - - a1 = A.getInstance() - a2 = A.getInstance() + super(Foo, self).__init__() + + a1 = Foo.get_instance() + a2 = Foo.get_instance() self.assertEquals(id(a1), id(a2)) - - def testInstantiateWithMultiArgConstructor(self): + + def testInstantiateWithMultiArgConstructor(self):#pylint: disable=C0103 """ If the singleton needs args to construct, include them in the first call to get instances. """ - - class B(Singleton): - + + class Bar(Singleton): + """Singleton child class.""" + def __init__(self, arg1, arg2): - super(B, self).__init__() + super(Bar, self).__init__() self.arg1 = arg1 self.arg2 = arg2 - - b1 = B.getInstance('arg1 value', 'arg2 value') - b2 = B.getInstance() + + b1 = Bar.get_instance('arg1 value', 'arg2 value') + b2 = Bar.get_instance() self.assertEquals(b1.arg1, 'arg1 value') self.assertEquals(b1.arg2, 'arg2 value') self.assertEquals(id(b1), id(b2)) - + def testInstantiateWithKeywordArg(self): - - class B(Singleton): - + """ + Test instantiation with keyword arguments. + """ + + class Baz(Singleton): + """Singleton child class.""" def __init__(self, arg1=5): - super(B, self).__init__() + super(Baz, self).__init__() self.arg1 = arg1 - - b1 = B.getInstance('arg1 value') - b2 = B.getInstance() + + b1 = Baz.get_instance('arg1 value') + b2 = Baz.get_instance() self.assertEquals(b1.arg1, 'arg1 value') self.assertEquals(id(b1), id(b2)) - + def testTryToInstantiateWithoutNeededArgs(self): - - class B(Singleton): - + """ + This tests, improper instantiation. + """ + + class Foo(Singleton): + """Singleton child class.""" def __init__(self, arg1, arg2): - super(B, self).__init__() + super(Foo, self).__init__() self.arg1 = arg1 self.arg2 = arg2 - - self.assertRaises(SingletonException, B.getInstance) - + + self.assertRaises(SingletonException, Foo.get_instance) + def testPassTypeErrorIfAllArgsThere(self): """ - Make sure the test for capturing missing args doesn't interfere with a normal TypeError. + Make sure the test for capturing missing args doesn't interfere + with a normal TypeError. """ - class B(Singleton): - + class Bar(Singleton): + """Singleton child class.""" def __init__(self, arg1, arg2): - super(B, self).__init__() + super(Bar, self).__init__() self.arg1 = arg1 self.arg2 = arg2 raise TypeError, 'some type error' - - self.assertRaises(TypeError, B.getInstance, 1, 2) - + + self.assertRaises(TypeError, Bar.get_instance, 1, 2) + def testTryToInstantiateWithoutGetInstance(self): """ Demonstrates that singletons can ONLY be instantiated through - getInstance, as long as they call Singleton.__init__ during construction. - - If this check is not required, you don't need to call Singleton.__init__(). + get_instance, as long as they call Singleton.__init__ during + construction. + + If this check is not required, you don't need to call + Singleton.__init__(). """ - - class A(Singleton): + + class A(Singleton): def __init__(self): super(A, self).__init__() - + self.assertRaises(SingletonException, A) - + def testDontAllowNew(self): - + def instantiatedAnIllegalClass(): - class A(Singleton): + class A(Singleton): def __init__(self): super(A, self).__init__() - - def __new__(metaclass, strName, tupBases, dct): - return super(MetaSingleton, metaclass).__new__(metaclass, strName, tupBases, dct) - + + def __new__(metaclass, str_name, tup_bases, dct): + return super(MetaSingleton, metaclass).__new__( + metaclass, str_name, tup_bases, dct) + self.assertRaises(SingletonException, instantiatedAnIllegalClass) - - + + def testDontAllowArgsAfterConstruction(self): - class B(Singleton): - + class B(Singleton): + def __init__(self, arg1, arg2): super(B, self).__init__() self.arg1 = arg1 self.arg2 = arg2 - - B.getInstance('arg1 value', 'arg2 value') + + B.get_instance('arg1 value', 'arg2 value') self.assertRaises(SingletonException, B, 'arg1 value', 'arg2 value') - + def test_forgetClassInstanceReferenceForTesting(self): - class A(Singleton): + class A(Singleton): def __init__(self): super(A, self).__init__() - class B(A): + class B(A): def __init__(self): super(B, self).__init__() - - # check that changing the class after forgetting the instance produces - # an instance of the new class - a = A.getInstance() + + # check that changing the class after forgetting the instance + # produces an instance of the new class + a = A.get_instance() assert a.__class__.__name__ == 'A' - A._forgetClassInstanceReferenceForTesting() - b = B.getInstance() + A._forget_class_instance_reference_for_testing() + b = B.get_instance() assert b.__class__.__name__ == 'B' - - # check that invoking the 'forget' on a subclass still deletes the instance - B._forgetClassInstanceReferenceForTesting() - a = A.getInstance() - B._forgetClassInstanceReferenceForTesting() - b = B.getInstance() + + # check that invoking the 'forget' on a subclass still deletes + # the instance + B._forget_class_instance_reference_for_testing() + a = A.get_instance() + B._forget_class_instance_reference_for_testing() + b = B.get_instance() assert b.__class__.__name__ == 'B' - + def test_forgetAllSingletons(self): # Should work if there are no singletons - forgetAllSingletons() - + _forget_all_singletons() + class A(Singleton): ciInitCount = 0 def __init__(self): super(A, self).__init__() A.ciInitCount += 1 - - A.getInstance() + + A.get_instance() self.assertEqual(A.ciInitCount, 1) - - A.getInstance() + + A.get_instance() self.assertEqual(A.ciInitCount, 1) - - forgetAllSingletons() - A.getInstance() + + _forget_all_singletons() + A.get_instance() self.assertEqual(A.ciInitCount, 2) - + def test_threadedCreation(self): - # Check that only one Singleton is created even if multiple - # threads try at the same time. If fails, would see assert in _addSingleton + # Check that only one Singleton is created even if multiple threads + # try at the same time. If fails, would see assert in _add_singleton class Test_Singleton(Singleton): def __init__(self): super(Test_Singleton, self).__init__() - + class Test_SingletonThread(threading.Thread): def __init__(self, fTargetTime): super(Test_SingletonThread, self).__init__() self._fTargetTime = fTargetTime self._eException = None - + def run(self): try: fSleepTime = self._fTargetTime - time.time() if fSleepTime > 0: time.sleep(fSleepTime) - Test_Singleton.getInstance() - except Exception, e: - self._eException = e - + Test_Singleton.get_instance() + except Exception, exc: + self._eException = exc + fTargetTime = time.time() + 0.1 lstThreads = [] for _ in xrange(100): @@ -429,80 +478,83 @@ if __name__ == '__main__': eException = t._eException if eException: raise eException - + def testNoInit(self): """ Demonstrates use with a class not defining __init__ """ - - class A(Singleton): + + class A(Singleton): pass - + #INTENTIONALLY UNDEFINED: #def __init__(self): # super(A, self).__init__() - - A.getInstance() #Make sure no exception is raised - + + A.get_instance() #Make sure no exception is raised + def testMultipleGetInstancesWithArgs(self): - + class A(Singleton): - + ignoreSubsequent = True - + def __init__(self, a, b=1): pass - - a1 = A.getInstance(1) - a2 = A.getInstance(2) # ignores the second call because of ignoreSubsequent - + + a1 = A.get_instance(1) + # ignores the second call because of ignoreSubsequent + a2 = A.get_instance(2) + class B(Singleton): - + def __init__(self, a, b=1): pass - - b1 = B.getInstance(1) - self.assertRaises(SingletonException, B.getInstance, 2) # No ignoreSubsequent included - + + b1 = B.get_instance(1) + # No ignoreSubsequent included + self.assertRaises(SingletonException, B.get_instance, 2) + class C(Singleton): - + def __init__(self, a=1): pass - - c1 = C.getInstance(a=1) - self.assertRaises(SingletonException, C.getInstance, a=2) # No ignoreSubsequent included - + + c1 = C.get_instance(a=1) + # No ignoreSubsequent included + self.assertRaises(SingletonException, C.get_instance, a=2) + def testInheritance(self): - """ + """ It's sometimes said that you can't subclass a singleton (see, for instance, http://steve.yegge.googlepages.com/singleton-considered-stupid point e). This test shows that at least rudimentary subclassing works fine for us. """ - + class A(Singleton): - - def setX(self, x): + + def set_x(self, x): self.x = x - + def setZ(self, z): raise NotImplementedError - + class B(A): - - def setX(self, x): + + def set_x(self, x): self.x = -x - - def setY(self, y): + + def set_y(self, y): self.y = y - - a = A.getInstance() - a.setX(5) - b = B.getInstance() - b.setX(5) - b.setY(50) + + a = A.get_instance() + a.set_x(5) + b = B.get_instance() + b.set_x(5) + b.set_y(50) self.assertEqual((a.x, b.x, b.y), (5, -5, 50)) - self.assertRaises(AttributeError, eval, 'a.setY', {}, locals()) + self.assertRaises(AttributeError, eval, 'a.set_y', {}, locals()) self.assertRaises(NotImplementedError, b.setZ, 500) unittest.main() - + |