[Fwd: Re: [Fwd: Possible bug in GLPK - Error detected in file env/alloc.c at line 72]]

[Andrew Makhorin]

-------- Forwarded Message --------
From: "Sierra Ansuas, Juan Pablo" <address@hidden>
To: Heinrich Schuchardt <address@hidden>, address@hidden <bug-glp
address@hidden>
Cc: Andrew Makhorin <address@hidden>, "Di Cristofaro, Milton Nadir" <MDiCr
address@hidden>
Subject: Re: [Fwd: Possible bug in GLPK - Error detected in file
env/alloc.c at line 72]
Date: Thu, 2 Apr 2020 18:14:30 +0000

> Dear Heinrich,
> 
> I have been working on the project that I have been assigned and
> applied the changes you suggested with successful results.
> 
> - glp_prob objects are created, used and deleted by the same thread
> - GLPK lib compiled with reentrancy support (checking whether to
> enable reentrancy support... yes)
> 
> The program is no longer crashing. Thank you.
> 
> I have looked at the multiseed.c example. The main difference between
> that example and the project that I am working on is that I build a
> glp_prob from scratch, then using glp_copy_prob make as many copies
> as processors are available on the machine. Each thread changes a
> couple values on the right hand side and runs the simplex again,
> without building the glp_prob again or starting the search from
> scratch.
> 
> However, the problem that I am now facing is that when several
> threads are calling glp_simplex at the same time, some values appear
> to be mixed up such as those returned by glp_get_row_dual. Adding a
> mutex (OMP CRITICAL) that contains only the glp_simplex call makes
> the problem go away and no issues can be seen, the program generates
> the expected output data and ends without errors.
> 
> I have looked at the error and output handling contained in the
> multiseed.c example. I ended up using glp_open_tee and redirecting
> the output of each thread to a separate file. No warnings were
> displayed.
> 
> Thank you very much for your help.
> 
> Regards,
> 
> Juan Pablo Sierra
> Desarrollo y Mantenimiento de Modelos
> DCU – Melilla – Montevideo
> Tel. (+598 2) 155 Int. 3777
> 
> 
> 
> 
> From: Heinrich Schuchardt <address@hidden>
> Sent: Thursday, March 26, 2020 6:46 PM
> To: address@hidden; Sierra Ansuas, Juan Pablo
> Cc: Andrew Makhorin
> Subject: Re: [Fwd: Possible bug in GLPK - Error detected in file
> env/alloc.c at line 72]
>  
> On 3/25/20 8:23 PM, Andrew Makhorin wrote:
> > -------- Forwarded Message --------
> > From: "Sierra Ansuas, Juan Pablo" <address@hidden>
> > To: address@hidden <address@hidden>
> > Cc: address@hidden <address@hidden>, "Di Cristofaro, Milton Nadir"
> <MDiCristo
> > address@hidden>
> > Subject: Possible bug in GLPK - Error detected in file env/alloc.c
> at
> > line 72
> > Date: Wed, 25 Mar 2020 18:34:56 +0000
> >
> >> Dear GLPK mantainer(s),
> >>
> >> I am having problems when trying to run the GLPK solver in a
> multi-
> >> threaded fashion using its C API and OpenMP. While the solver does
> >> appear to work, an error comes up when trying to free the memory
> with
> >> glp_delete_prob:
> >>
> >> glp_free: memory allocation error
> >> Error detected in file env/alloc.c at line 72
> >>
> >> I am no GLPK expert but I would be very grateful if you could
> check
> >> the provided source code and determine whether this is being
> caused
> >> by a bug or a simple beginner mistake.
> >>
> >> Running on an eight core processor, 8GiB ram. Stack size limit:
> 2GB
> >> (ulimit -s 2000000), Stack size limit per thread: 200MB (export
> >> OMP_STACKSIZE=200000). Provided source makes little sense but is
> >> quite short and reproduces the problem every time. Compile command
> is
> >> as follows:
> >>
> >> gcc test_c.c  -o test_c -fopenmp -I/home/user/libglpk/glpk-
> >> 4.65/include /home/user/libglpk/glpk-
> 4.65/src/.libs/libglpk.so.40.3.0
> >>
> >>
> >> Regards,
> >>
> >> Juan Pablo Sierra
> 
> Hello Juan,
> 
> Did you compile GLPK with '--enable-reentrant=yes'?
> 
> You are creating all problems in one thread and then call the solver
> in
> separate threads. This is not supported by GLPK.
> 
> Please, have a look at:
> glpk-4.65/examples/threads/multiseed.c
> 
> Here all GLPK library calls needed for each individual model are
> called
> within the same separate thread.
> 
> Please, have a look at the error and output handling in the example
> too.
> 
> Best regards
> 
> Heinrich
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