messagebuffer.py

import logging
from tornado.concurrent import Future

class MessageBuffer(object):
    def __init__(self):
        self.waiters = set()
        self.cache = []
        self.cache_size = 80

    def wait_for_messages(self, cursor=None):
        # Construct a Future to return to our caller.  This allows
        # wait_for_messages to be yielded from a coroutine even though
        # it is not a coroutine itself.  We will set the result of the
        # Future when results are available.
        result_future = Future()
        if cursor:
            new_count = 0
            for msg in reversed(self.cache):
                if msg["id"] == cursor:
                    break
                new_count += 1
            if new_count:
                result_future.set_result(self.cache[-new_count:])
                return result_future
        self.waiters.add(result_future)
        return result_future

    def cancel_wait(self, future):
        self.waiters.remove(future)
        # Set an empty result to unblock any coroutines waiting.
        future.set_result([])

    def new_messages(self, messages):
        logging.info("Sending new message to %r listeners", len(self.waiters))
        for future in self.waiters:
            future.set_result(messages)
        self.waiters = set()
        self.cache.extend(messages)
        if len(self.cache) > self.cache_size:
            self.cache = self.cache[-self.cache_size:]