Re: Interrupting GLPK on demand

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
> [email protected]
> https://lists.gnu.org/mailman/listinfo/help-glpk
>


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