def __init__(self, todo_tasklet, limit):
self._todo_tasklet = todo_tasklet<EOL>self._limit = limit<EOL>self._queues = {}<EOL>self._running = []  <EOL>self._cache = {}<EOL>
Init.

        Args:
          todo_tasklet: the tasklet that actually fires RPC and waits on a MultiRPC.
            It should take a list of (future, arg) pairs and an "options" as
            arguments. "options" are rpc options.
          limit: max number of items to batch for each distinct value of "options".