Re: [Help-glpk] Error detected in file glplib10.c at line 109

[Antonello Lobianco]

Hello, I created a test case where I apply a loop over a SINGLE working thread that solves the LP example and I still have the issue.

Now I don't know if the problem is (in inverted order of estimated likelihood):

1) in my code;
2) in the Qt thread library;
3) in glpk;
4) somewhere in the compiler (gcc version 4.4.1 (Ubuntu 4.4.1-4ubuntu8) )

The code is downloadable at http://grecof2.econ.univpm.it/~lobianco/public/qtglpk.tgz but busically the core is:

#include <iostream>
#include <stdio.h>
#include <cstdlib>
#include <glpk.h>
#include <Thread.h>

using namespace std;

int main(int argc, char *argv[]){

    cout << "Test on a glpk application using Qt Threads" << endl<<endl;

    Thread wThread;  // Thread is a subclass of QThread
    for (uint y=0;y<500;y++){
        bool assigned = false;
        while(!assigned) {
            if (!wThread.isRunning()){
                wThread.start(); // job done from the other thread.. just solve the glpk LP example

                assigned = true;
                break;
            } 
        }
    }
    
    cout <<"All done without errors (crashing)"<<endl;

    return 0;
}

/Antonello

On Fri, Nov 20, 2009 at 5:49 AM, Andrew Makhorin <address@hidden> wrote:

>     I am trying to parallelise the Qt/C++ code of  multi agent model
> representing farmers.

> For the time being I #39;m using only 1 thread as I got from this

> list that glpk is, at the present time, not  re-entrant.
> The funny(!) side is that when I use the new code (see down), even
> if it use only **1** working threads, the unpatched version of glpk
> crash.
> I used then the doc example and I was able to receive the following error message when crashing:
> Assertion failed: xlcmp(env->t_last, t) <= 0
> Error detected in file glplib10.c at line 109

> Is it a glpk bug or something I am doing seriously very wrong ??

I don't think it is a glpk bug. Something unpredictable occured,
because original glpk code is not re-enterable.

You can make glpk re-enterable by replacing src/glplib02.c with a
re-enterable version (for details see comments). However, glpk has
no synchronization features, so the same problem object must not be
used in different threads.

-- 
Antonello Lobianco
Assegnista di Ricerca
Dipartimento di Economia, Università Politecnica delle Marche
Progetto "RegMAS per il Piceno" (Fondazione CARISAP)

Tel: +39.071.2207116
Email: address@hidden