Bug #1015: Bruns SEGV: SparsePolyIter/DMPI problem - CoCoALib - CoCoA Project

Bug #1015

Bruns SEGV: SparsePolyIter/DMPI problem

Added by John Abbott about 7 years ago. Updated almost 7 years ago.

Status:

Closed

Priority:

Normal

Assignee:

John Abbott

Category:

Data Structures

Target version:

CoCoALib-0.99550 spring 2017

Start date:

01 Mar 2017

Due date:

% Done:

100%

Estimated time:

6.01 h

Spent time:

6.15 h

Description

Winfried Bruns reported a SEGV problem by email.

The following code will exhibit it: F is a poly with a single term in a DMPI ring.
Either monomial or the assignment triggers SEGV.

void john(const RingElem& F)
{
    SparsePolyRing P=owner(F);
    long dim=NumIndets(P);
    vector<long> v(dim);
    SparsePolyIter it=BeginIter(F);
    exponents(v,PP(it));
    vector<RingElem> junk(1, zero(P));
    junk[0] =  monomial(P,coeff(it), v);
}

Related issues

History

#1 Updated by John Abbott about 7 years ago

Status changed from New to In Progress
% Done changed from 0 to 10

The problem arises under the following conditions:

CoCoALib is configured with --threadsafe-hack and --no-boost
compilation of CoCoALib is with optimization; problem does not arise if compiled without -O2

COmpilation of test program is with the following command:

g++ -std=c++11 -O3 -Wno-deprecated-declarations -Wall -pedantic -funroll-loops -g -I /home/jabbott/Work/CoCoALib-0.99/include -I .  CoCoATest.C  /home/jabbott/Work/CoCoALib-0.99/lib/libcocoa.a -lgmpxx -lgmp -o CoCoATest

Working to narrow down the problem.

#2 Updated by John Abbott about 7 years ago

Here we have a minimal failing example:

  {
    GlobalManager CoCoAFoundations;

    SparsePolyRing R=NewPolyRing_DMPI(RingQQ(),1);
    const RingElem& F = one(R);

    SparsePolyIter it=BeginIter(F);
    cout <<    coeff(it) << endl;
    cout <<  "R is .." <<endl;
    cout <<  R <<endl;
  }

It fails in the last line@ whether we print coeff(it) or PP(it).

#3 Updated by John Abbott about 7 years ago

The problem continues to arise with the following simplified compilation command:

g++ -g -I /home/jabbott/Work/CoCoALib-0.99/include -I .  CoCoATest.C  /home/jabbott/Work/CoCoALib-0.99/lib/libcocoa.a -lgmp -o CoCoATest

JAA thinks it is very likely that there is a problem with SparsePolyIter over a DMPI. Tracking it down will be "fun" 8-{
NOTE the problem arises with g++ versions 5.3.1 and 6.2.1, so is almost certainly out fault :-/

#4 Updated by John Abbott about 7 years ago

Status changed from In Progress to Resolved
% Done changed from 10 to 50

The problem goes away if the flag -DCoCoA_THREADSAFE_HACK is added to the compilation line.

At the moment I do not know how I can protect a user against such an omission.

#5 Updated by John Abbott about 7 years ago

Assignee set to John Abbott
% Done changed from 50 to 90

I have now added an automatic check for CoCoA_THREADSAFE_HACK.
If you compile the library with one setting and try to compile an application with a different setting then you should get a compile time error (when trying to create a GlobalManager).

I'll check in soon, and may send a trial version to Winfried.