[IPython-dev] Kernel-client communication

[Almar Klein]

Hi Hans,

On 3 September 2010 11:18, Hans Meine <hans_meine at gmx.net> wrote:

> Am Freitag 03 September 2010, 10:30:29 schrieb Almar Klein:
> > * You plan on keeping history in the kernel. In this case I think this is
> > the task of the client. Otherwise you'd get your own history mixed with
> > that of someone else using that kernel? History is, I think, a feature of
> > the client to help the programmer. I see no use for storing it at the
> > kernel.
>
> That's an interesting issue.  Some more random thoughts:
>
> - If you decide to connect to an existing session (from home or the bar via
> your smartphone) to check something and/or issue a command, it is very
> useful
> to reuse your existing history -> should be in the kernel
>

You're right, that makes sense too.



> - If you are using only one frontend/client, it does not matter anyhow,
> only..
>
> - If the kernel is busy, it could still be useful to browse through the
> history to compose the next command(s) -> should be in the client?
>

Well,  the kernel could be implemented in such a way that messages are
received in a separate thread, which may also handle the introspection
requests. Introspection (+history) will then still work if the process is
busy (unless it's running extension code).


- In the multiple GUI/observer scenario, I think it would not hurt to share
> the history with the observer either -> could be in the kernel
>


> Is there any other reason to have the history in the client, Almar?
>
> Otherwise, I's say of course it's a feature of the client, but obviously
> there
> are good reasons (in particular when detaching/attaching) to have the
> history
> be stored in the kernel.  Maybe it needs to be duplicated/synchronized to
> support situations where the kernel cannot respond, though.
>

It seemed intuitively more correct (it still does, to me), but in practice
it may be better to store it in the kernel. Thanks for enlightening me!

  Almar
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