[Osi] [Clp] OsiClp causes crash when deleting OsiCLPSolverInterface. Reason: borrowModel?

[John Forrest]

Torsten,

CBC 2.1 is rather old.

Try going to a newer version of Cbc (2.3 onwards) (for a newer version
of OsiClpSolverInterface.cpp).  Then you can add

mySolver->setSpecialOptions(mySolver->specialOptions()|1024);

to your code.

That should not do the borrowModel which will save you memory and should
also fix bad pointer problem.

If you need to stay with Cbc 2.1 then I have modified
OsiClpSolverInterface.cpp so setSpecialOptions should work.

John Forrest

On Mon, 2010-10-25 at 16:25 +0200, Torsten Fahle wrote:
> Hi there,
> 
> we found a problem with some large LP-Model that is transferred to CLP via Osi-Interface.
> The problems occurs with Clp, Osi, Coin from the CBC 2.1.0 distribution.
> 
> We use an OsiClpSolverInterface, create a model and solve it via initialSolve.
> 
> During initialSolve, some memory allocation fails and a bad_alloc exception is
> thrown which we catch in our application. 
> At that moment, however, our OsiClpSolverInterface object is corrupt so that calling delete on that
> object causes an "Access vialotaion" followed by an application crash.
> 
> 
>      OsiClpSolveInterface mySolver = new OsiClpSolverInterface;
>      [...]
> 
>      [generate CoinModel myModel]
> 
>      mySolver->loadFromCoinModel(myModel);
> 
>      try {
>         mySolver->initialSolve();
>      }
>      catch (bad_alloc)
>     {
>         cout << "Bad Alloc" << endl;
>     }
>     [...]
>    delete mySolver;  // <<<==== ACCESS VIOLATION, because ModelPtr->clpMatrix is invalid
> 
> 
> After some deeper look into what's happening the reason seems to be the 
> borrwoModel/returnModel mechanism:
> 
> The OsiClpSolverInterface holds a modelPtr can contains (among others) our clp-matrix.
> 
> When calling OsiClpSolverInterface->initialSolve()  [OsiClpSolverInterface.cpp, l. 48]
> a ClpSimplex object named solver is created  [OsiClpSolverInterface.cpp, l. 50]
> that borrows the modelPtr [OsiClpSolverInterface.cpp, l. 52].
> 
> In [OsiClpSolverInterface.cpp, l. 162]  ClpPresolve is prepared and called.
> During that call, presolve fails to allocate memory in  [CoinPresolveImpliedFree.cpp, l. 521], 
> called from [ClpPresolve.cpp 546].
> 
> Now, a bad_alloc exception is thrown and all objects on the call stack are destroyed up to the 
>  try/catch block in our application. During that unwinding and cleaning, also the borrowed modelPtr
> is deleted although not owned by solver. 
> Because the ecxeption causes an immediate unrolling of the call stack "returnModel" is not called.
> 
> When our application later on tries to delete the correctly allocated OsiClpSolverInterface, the destructor 
> tries to delete the modelPtr and that causes the "access violation" described above.
> 
> Question: 
> Would it be possible to make the borrowModel/returnModel mechanism more robust?
> E.g. borrowModel could also set a bool indicating that the model is only borrowed, and a destructor
> triggered e.g. by the  exception cleanup could check first whether that model is owned or borrowed.
> 
> Thanks
> 
>  Torsten
> 
> 
> 
> 
>