Question

My program exits when main function tries to run some class (Rock) more than once with a double free or corruption glibc error.

Valgrind returns:

==18672== Conditional jump or move depends on uninitialised value(s)
==18672==    at 0x56F8554: std::ostreambuf_iterator<char, std::char_traits<char> > std::num_put<char, std::ostreambuf_iterator<char, std::char_traits<char> > >::_M_insert_int<unsigned long>(std::ostreambuf_iterator<char, std::char_traits<char> >, std::ios_base&, char, unsigned long) const (in /usr/lib64/libstdc++.so.6.0.17)
==18672==    by 0x56F876C: std::num_put<char, std::ostreambuf_iterator<char, std::char_traits<char> > >::do_put(std::ostreambuf_iterator<char, std::char_traits<char> >, std::ios_base&, char, unsigned long) const (in /usr/lib64/libstdc++.so.6.0.17)
==18672==    by 0x56FB945: std::ostream& std::ostream::_M_insert<unsigned long>(unsigned long) (in /usr/lib64/libstdc++.so.6.0.17)
==18672==    by 0x431515: Rock::saveClustering(std::set<Attribution, std::less<Attribution>, std::allocator<Attribution> >) (rock.cpp:1406)
==18672==    by 0x430C66: Rock::startRock() (rock.cpp:1321)
==18672==    by 0x45DABC: main (main.cpp:207)
==18672==  Uninitialised value was created by a stack allocation
==18672==    at 0x42FF39: Rock::getFinalList(std::vector<Rock::BestLabel, std::allocator<Rock::BestLabel> >&) (rock.cpp:1139)
==18672== 
==18672== 
==18672== HEAP SUMMARY:
==18672==     in use at exit: 292 bytes in 11 blocks
==18672==   total heap usage: 86,558 allocs, 86,547 frees, 21,133,326 bytes allocated
==18672== 
==18672== 292 (52 direct, 240 indirect) bytes in 1 blocks are definitely lost in loss record 11 of 11
==18672==    at 0x4C2BCFB: malloc (vg_replace_malloc.c:270)
==18672==    by 0x5F7FC94: nss_parse_service_list (in /lib64/libc-2.15.so)
==18672==    by 0x5F80173: __nss_database_lookup (in /lib64/libc-2.15.so)
==18672==    by 0xC1C15DB: ???
==18672==    by 0x5F3592B: getpwuid_r@@GLIBC_2.2.5 (in /lib64/libc-2.15.so)
==18672==    by 0x5050638: pqGetpwuid (in /opt/postgres_home/lib/libpq.so.5.3)
==18672==    by 0x503C3BD: pqGetHomeDirectory (in /opt/postgres_home/lib/libpq.so.5.3)
==18672==    by 0x503CCD4: getPgPassFilename (in /opt/postgres_home/lib/libpq.so.5.3)
==18672==    by 0x503F78A: PasswordFromFile (in /opt/postgres_home/lib/libpq.so.5.3)
==18672==    by 0x503FAAB: connectOptions2 (in /opt/postgres_home/lib/libpq.so.5.3)
==18672==    by 0x503FD77: PQconnectStart (in /opt/postgres_home/lib/libpq.so.5.3)
==18672==    by 0x503FDA5: PQconnectdb (in /opt/postgres_home/lib/libpq.so.5.3)
==18672== 
==18672== LEAK SUMMARY:
==18672==    definitely lost: 52 bytes in 1 blocks
==18672==    indirectly lost: 240 bytes in 10 blocks
==18672==      possibly lost: 0 bytes in 0 blocks
==18672==    still reachable: 0 bytes in 0 blocks
==18672==         suppressed: 0 bytes in 0 blocks

I’m not used to Valgring. Does it say that there was unitialized memory that was not free regarding postgres database access? The method I used to fetch the data was:

void Comum::fetchDB ( string sql_statement )
{
    string conn_str ( "dbname=" + getDbName() + " user=" + getDbUser() );
    pqxx::connection conn (conn_str);
    pqxx::work txn (conn);              // ex: domain = "voice"
    pqxx::result r = txn.exec (sql_statement);

    if ( r.size () == 0 ) {
        std::cerr << "No records found for '" << domain << "'." << endl;
        exit (12);
    }

    txn.commit ();

    for (unsigned int u = 0; u != getNrFields (); ++u) {
        vector <string> v;
        v.reserve (r.size());
        db_fetched.push_back (v);
    }

    for (unsigned int rownum = 0; rownum != r.size(); ++rownum) {
        const pqxx::result::tuple row = r[rownum];

        for (unsigned int colnum = 0; colnum != row.size(); ++colnum) {
            const pqxx::result::field f = row[colnum];
            db_fetched [colnum].push_back( f.c_str() );
        }
    }
    conn.disconnect();
}

Regarding the first line of Valgrind’s output Conditional jump or move depends on unitialized value(s) the saveClusteringmethod is like follows:

void Rock::saveClustering (const set<Attribution> result)
{
    string rock_dir = "rock";
    string parent_dir = "output";
    string dir = parent_dir + "/" + rock_dir;

    // Create directory.
    createDir (parent_dir);
    createDir (dir);

    // Build filename.
    string filename;

    map<unsigned int, AttType>::const_iterator citype = att_type.begin();
    while (citype != att_type.end()) {
        filename += citype->second.getName();
        if (++citype != att_type.end()) {
            filename += "-";
        }
    }

    filename = parent_dir + "/" + rock_dir + "/" + filename + "-" + currentDateTime() + ".txt";
    ofstream myfile(filename.c_str());

    if (myfile.is_open()) {
        for ( set<Attribution>::const_iterator ci = result.begin();ci != result.end(); ++ci ) {
            myfile << ci->id << "\t";

            for (vector<unsigned int>::const_iterator enci = ci->encodings.begin(); enci != ci->encodings.end(); ++enci) {
                myfile << *enci << "\t";
            }

            myfile << ci->type << "\t" << ci->assignment << endl;  // 1406 LINE
        }
        myfile << endl;
        myfile.close();

    } else {
        cerr << "It was not possible to save decoder filename " << filename << endl;
        cerr << "Press any key <ENTER> to continue.";
    }
}

I just can’t see what’s wrong and can’t provide a small workable program.

Answer 1

There are two separate problems in the valgrind output.

The first is the use of uninitialized memory, which it tells you was created on the stack at rock.cpp line 1139

==18672==    at 0x42FF39: Rock::getFinalList(std::vector<Rock::BestLabel, std::allocator<Rock::BestLabel> >&) (rock.cpp:1139)

Look at that line and initialize the variable.

The second problem is a memory leak, apparently from the Postgres API. That’s almost certainly not the cause of your crash.

Neither of these looks like the cause of a double free error, that’s most likely caused by not implementing a correct copy constructor or copy assignment operator in your class.