async.py 文件源码

def call_singleton(self, function, identifier, *args, **kwargs):
        """
        Executes *function* if no other function with the given *identifier*
        is already running.  If a function is currently running with the given
        *identifier* the passed *function* will be called when the first
        function is complete.

        In other words, functions called via this method will be executed in
        sequence with each function being called after the first is complete.

        The function will be passed any given *args* and *kwargs* just like
        :meth:`AsyncRunner.call`.

        If 'callback' is passed as a keyword argument (*kwargs*) it will be
        called with the result when complete.
        """
        callback = kwargs.pop('callback', None)
        if identifier in ONE_CALLS:
            ONE_CALLS[identifier]['queue'].append(
                (function, args, kwargs, callback))
        else:
            from collections import deque
            future = self.executor.submit(safe_call, function, *args, **kwargs)
            ONE_CALLS[identifier] = {
                'future': future,
                'queue': deque()
            }
            if callback:
                done_callback(
                    ONE_CALLS[identifier]['future'],
                    lambda f: callback(f.result()))
            completed = partial(_call_complete, self, identifier)
            done_callback(ONE_CALLS[identifier]['future'], completed)
        #print 'ONE_CALLS',ONE_CALLS
        #print 'identifier',identifier
        return ONE_CALLS[identifier]['future']