Get the value from the API. Make sure to use a lock in order not to
        fetch the value twice at the same time.

async def get_value(self):
        """
        Get the value from the API. Make sure to use a lock in order not to
        fetch the value twice at the same time.
        """

        cc = self.request.custom_content

        async with self.lock:
            if self.content_key not in cc:
                cc[self.content_key] = await self.call_api()

        return cc[self.content_key]