Question

当main函数尝试以double free or corruption glibc错误多次运行某个类（Rock）时，我的程序退出。

Valgrind回归：

==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

我不习惯Valgring。是否说有关于postgres数据库访问的单元化内存不是免费的？我用来获取数据的方法是：

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();
}

关于Valgrind输出Conditional jump or move depends on unitialized value(s)的第一行，saveClustering方法如下：

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.";
    }
}

我只是看不出有什么不对，无法提供一个小的可行程序。

Answer 1

valgrind输出中存在两个不同的问题。

第一个是使用未初始化的内存，它告诉你是在rock.cpp行1139

的堆栈上创建的

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

查看该行并初始化变量。

第二个问题是内存泄漏，显然来自Postgres API。这几乎肯定不是你崩溃的原因。

这些都不是导致双重自由错误的原因，这很可能是因为没有在您的班级中实现正确的复制构造函数或复制赋值运算符。

双重免费或腐败错误 - valgrind

1 个答案: