# Copyright 2017, David Wilson
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from __future__ import absolute_import
import mitogen.service


class ContextService(mitogen.service.DeduplicatingService):
    """
    Used by worker processes connecting back into the top-level process to
    fetch the single Context instance corresponding to the supplied connection
    configuration, creating a matching connection if it does not exist.

    For connection methods and their parameters, refer to:
        https://mitogen.readthedocs.io/en/latest/api.html#context-factories

    This concentrates all SSH connections in the top-level process, which may
    become a bottleneck. There are multiple ways to fix that: 
        * creating one .local() child context per CPU and sharding connections
          between them, using the master process to route messages, or
        * as above, but having each child create a unique UNIX listener and
          having workers connect in directly.

    :param dict dct:
        Parameters passed to `mitogen.master.Router.[method]()`.

        * The `method` key is popped from the dictionary and used to look up
          the Mitogen connection method.
        * The `discriminator` key is mixed into the key used to select an
          existing connection, but popped from the list of arguments passed to
          the connection method.

    :returns mitogen.master.Context:
        Corresponding Context instance.
    """
    handle = 500
    max_message_size = 1000
    required_args = {
        'method': str
    }

    def get_response(self, args):
        args.pop('discriminator', None)
        method = getattr(self.router, args.pop('method'))
        return method(**args)