Re: [Jython-dev] Nobody uses SystemRestart

[Jim B. <jim...@py...>]

Jeff,

My first thought here is as follows: If there's no breaking test, then the
feature was not implemented. I say this of course as the person who
inadvertently nuked it :)

The rest of the problems you raise are also highly fatal to resurrecting
this feature. So I would suggest that you please do not restore.

- Jim


On Tue, Sep 4, 2018 at 1:55 PM, Jeff Allen <ja...@fa...> wrote:

> I know this because it hasn't worked since 2014 and no-one has complained.
> Should we keep it?
>
> First, some archaeology ... Restarting was introduced by Leo Soto in 2008
> (rationale here: https://codereview.appspot.com/2810) and is still marked
> as "experimental". Along the way it has had some work including the
> introduction of shutdownInterpreter() here: https://hg.python.org/jython/
> rev/94b5f009fb77#l3.36 and the accompanying socket._closeActiveSockets()
> that it calls. The motivation is to restart Jython when used in a
> web-server without incurring the application start-up time. Fast-forward to
> 2014 and _closeActiveSockets gets blown away (
> https://hg.python.org/jython/rev/107fe4a4c96b). From here on, raising
> SystemRestart gets you an NPE, but nobody notices that. Here it is in 2.7.0:
>
> PS startup2> jython test_restart.py
> Exception in thread "MainThread" java.lang.NullPointerException
>         at org.python.util.jython.shutdownInterpreter(jython.java:439)
>         at org.python.util.jython.run(jython.java:372)
>         at org.python.util.jython.main(jython.java:142)
>
> Restart gets a mention here: http://bugs.jython.org/issue1475 so it was
> used in 2.5.1 ...
>
> I can keep it (really, restore it) but I'm not sure what to do to
> reproduce the missing _closeActiveSockets() or whether it matters. Just for
> now I've made the absence non-fatal while I work on the rest of
> http://bugs.jython.org/issue2686.
>
> I think the idea of this has a couple of flaws we cannot easily get around.
>
>    - It is not compatible with the idea of multiple interpreters
>    (multiple sys modules). A restart, invoked by one interpreter, stops *all*
>    Jython threads, cleans up *one* interpreter, and restarts the *whole*
>    application.
>    - Static initialisation is not reset unless you know to do it. Some
>    static initialisation (the type system, loaded classes) is intentionally
>    preserved because it drives the start-up time we're trying to save. But
>    others (initially empty lists in sys, Options flags, the registry) can trip
>    up the interpreter on a second pass. Every such case I find has an easy
>    corrective: countless others are waiting to pounce.
>
> Any thoughts on this experiment?
>
> Jeff
>
> --
> Jeff Allen
>
>