Messages were queued by the messages sent timestamp in the message header as
well as based on the channel the message was received on because there is no
guarantee on the order of the received messages. This matters because a request
is dropped from a client's request table when an idle message is received, but
this idle message is not guaranteed to be the last message received for a
request, for example a reply message may come after the idle message has been
received.
Now if a request has received an idle message already, instead of
dropping it immediately, drop it only when the last received message time for
the request is longer than a few seconds.
Handler methods are only run on a successful request. If an error occurs during
execution an error message is emitted on the IOPub channel, this is where
errors are handled. Or they can be captured in the reply messages through
callbacks.
`jupyter-inhibit-handlers` can now be a list of message types. If a message is
received and has one of these message types, then the client handler
corresponding to that message type is prevented from running.
Setup the necessary hooks before starting the kernel so that we can ensure that
the startup message is caught.
A short delay is also added whenever we start a channel. This was necessary for
the client to catch the startup message of a python kernel.
- Distinguish between an asynchronous channel and a synchronous one
- `jupyter-async-channel` :: Messages are sent and received through an ioloop
subprocess that the channel has access to. The
subprocess uses the `jupyter-sync-channel` for
sending and receiving messages.
- `jupyter-sync-channel` :: Messages are sent and received through a
`zmq-socket` in the current Emacs session.
- Define `jupyter-send` and `jupyter-recv` methods for channels.
- Update `jupyter-kernel-client` and ioloop interfaces to take into account
changes with channels.
Since client local variables are associated with a buffer a buffer needs to be
present when the client is first initialized. This buffer is also used as the
process buffer of the ioloop subprocess.
