cache.py 文件源码

def safe_apply(self, key, function, default_value=None):
            """
            Safely apply a function to the value of a key in storage and set
            the return value of the function to it.

            Return the result of applying the function.
            """
            key = self.key_filter_in(key)
            exists = True
            try:
                val_file = recfile.open(key, mode='r+b', path=self.folder)
            except IOError:
                exists = False
                val_file = recfile.open(key, mode='wb', path=self.folder)
            self.wait_portalock(val_file)
            if exists:
                timestamp, value = pickle.load(val_file)
            else:
                value = default_value
            new_value = function(value)
            val_file.seek(0)
            pickle.dump((time.time(), new_value), val_file, pickle.HIGHEST_PROTOCOL)
            val_file.truncate()
            val_file.close()
            return new_value