Re: [Help-glpk] Interrupting GLPK on demand

[Szabolcs Horvát]

Hello Heinrich,

Thanks for the suggestion.

Would this method not prevent any allocated memory from being cleaned
up? I am not very familiar with GLPK yet, but the need for
setjmp/longjmp suggests that any cleanup steps would be skipped.

Best regards,
Szabolcs

On Mon, 14 Oct 2019 at 19:11, Heinrich Schuchardt <address@hidden> wrote:
>
> Hello Szabolcs,
>
> you can create a terminal hook function (see glp_term_hook()). In this
> hook function you can trigger an abort using glp_error(). Use a error
> hook function (see glp_error_hook()) to catch the error and longjmp() to
> return to the setjmp() in the calling program.
>
> An example in Java is available as:
>
> https://sourceforge.net/p/glpk-java/code/HEAD/tree/trunk/examples/java/GmplSwing.java
>
> An example for an error hook function in C is available as:
>
> https://sourceforge.net/p/winglpk/code/HEAD/tree/trunk/examples/c/glp_error_hook_demo.c
>
> Best regards
>
> Heinrich
>
> On 10/14/19 2:45 PM, Szabolcs Horvát wrote:
> > Hello,
> >
> > Is there a way to interrupt GLPK without killing the entire process?
> >
> > I am interested in terminating glp_intopt(). In principle, this is
> > possible by calling glp_ios_terminate() from the callback function
> > passed to glp_intopt(). However, glp_intopt() will internally call
> > glp_simplex(), which may take a very long time. Thus in practice this
> > does not work. I could not find any way to interrupt glp_simplex() on
> > demand.  It is possible to set a time limit (tm_lim in glp_smcp), but
> > this is not what I need. I would like to have the ability to
> > interactively interrupt the computation.
> >
> > For example, glp_simplex() could periodically call a user-supplied
> > function. If this function returns "true", the computation should be
> > interrupted gracefully.
> >
> > I do not need a partial result to be returned. I simply need a clean
> > interruption, with the resources used by the function properly cleaned
> > up (e.g. no unreleased memory). I assume that this is possible, since
> > a time limit is already implemented. In principle, I could even look
> > up the part of the code that checks the time, and add an additional
> > interruption check. I am wondering why this wasn't implemented
> > already, and whether simply doing this would cause any problems. Some
> > old messages posted to this mailing list seem to suggest that
> > implementing interruption may not be easy, which seems to be in
> > contradiction with the fact that a time limit is already implemented.
> > https://lists.gnu.org/archive/html/help-glpk/2006-04/msg00059.html
> >
> > Summary:
> >
> >   - Is there a way to interrupt glp_intopt() cleanly and reliably?
> >   - If not, consider this a feature request. Please add this functionality.
> >   - Would there be an issue with extending the time-limit check to also
> > call a user-supplied interruption-check function?
> >
> > Use case:
> >
> > I am not very familiar with ILP solvers. I am actually using graph
> > theory code that relies on GLPK. I am using this code from a
> > high-level language that is typically used interactively (think Python
> > in a Jupyter notebook). Given the nature of the problems that GLPK
> > solves, it is very hard to predict how long a computation would take.
> > It could be seconds or days. Therefore, it is important to be able to
> > interrupt computations gracefully, without needing to kill the entire
> > session.
> >
> > In particular, this problem came up while working on the igraph
> > library: https://github.com/igraph/igraph/issues/897
> >
> > Best regards,
> > Szabolcs
> >
> > _______________________________________________
> > Help-glpk mailing list
> > address@hidden
> > https://lists.gnu.org/mailman/listinfo/help-glpk
> >
>