MC Lock Decorator

mc_lock.py

#====== Decorator to use memcached for locking =======

def mc_lock(namespace, on_lock_failed) :
    '''
    This uses memcached to provide a lock on a key before performing some operation.
    The first argument provided to the decorated function will be the key.
    It will be preceded by $namespace to ensure uniqueness
    on_lock_failed is a function that will be called if we fail to acquire the lock
    '''

    def my_decorator(func) :

        def wrapped(*args, **kwargs) :
            if not args:
                raise Exception("You must pass an un-named arg to use mc_lock on!")
            lock_mc_key = _utf8('%s.%s' % (namespace, args[0]))
            if mc.add(lock_mc_key, 1, time=300):
                try:
                    return func(*args, **kwargs)
                finally:
                    mc.delete(lock_mc_key)
            else:
                on_lock_failed()
        return wrapped

    return my_decorator


# ====================================================