[Boost-users] [smart_ptr] shared_ptr clean-up failure

From: Robbie Morrison (robbie_at_[hidden])
Date: 2007-10-04 14:28:31

Hi all -- hope someone can help, many TIA -- Robbie

Intro

  This relates to the Boost.Smart_ptr library.

  The example code (see below) fails when a
  boost::shared_ptr is used, but not when a raw pointer
  is substituted.

  This posting probably highlights some key
  misunderstanding on my part.  Perhaps someone can
  explain where I went wrong.

  As a long shot, it could be that the Boost.Ref library
  can offer something useful.

Problem

  I want to pass in an existing UDT (user-defined type)
  by reference to a second UDT during construction.  I
  figured it would be better to hold this reference in
  a smart pointer rather than a raw pointer.

  The following stripped-down code mimics this process,
  but passes in an int (a fundamental type) instead for
  reasons of simplicity.

  The example works fine with a raw pointer, but not a
  boost::shared_ptr (or std::auto_ptr or
  boost::scoped_ptr or std::tr1::shared_ptr).

  I checked in Becker (2007) ("C++ standard library
  extensions") and Karlsson (2006) ("Beyond the C++
  standard library") regarding Boost.Smart_ptr's, but
  could not see anything useful.

  'frag-pass-by-ref_03.cc' was the name of my program.

Test environment

  - Boost release 1.34.1 dated 24-Jul-2007 (source build)
  - GNU GCC 4.1.2 compiler (using -Wall -Weffc++ -pedantic)
  - Linux Ubuntu 6.10 operating system (now superseded by 7.04)
  - run-time memory checking with valgrind version "valgrind-3.2.0-Debian"
  - laptop is Toshiba Tecra A2 330, new 2004, 1.4GHz Intel Celeron M

Error messages (normal run-time)

  destroying a MyClass
  *** glibc detected *** ./frag-pass-by-ref_03: free(): invalid pointer: 0xbfcd12dc ***
  ======= Backtrace: =========
  /lib/tls/i686/cmov/libc.so.6[0xb7d8a8bd]
  /lib/tls/i686/cmov/libc.so.6(__libc_free+0x84)[0xb7d8aa44]
  /usr/lib/libstdc++.so.6(_ZdlPv+0x21)[0xb7f3afc1]
  ./frag-pass-by-ref_03(__gxx_personality_v0+0x3d3)[0x8048baf]
  ./frag-pass-by-ref_03[0x8048c96]
  ./frag-pass-by-ref_03(__gxx_personality_v0+0x274)[0x8048a50]
  ./frag-pass-by-ref_03(__gxx_personality_v0+0x29e)[0x8048a7a]
  ./frag-pass-by-ref_03(__gxx_personality_v0+0x2ba)[0x8048a96]
  ./frag-pass-by-ref_03[0x8048cd4]
  ./frag-pass-by-ref_03(__gxx_personality_v0+0x195)[0x8048971]
  /lib/tls/i686/cmov/libc.so.6(__libc_start_main+0xdc)[0xb7d398cc]
  ./frag-pass-by-ref_03(__gxx_personality_v0+0x65)[0x8048841]
  ======= Memory map: ========
  (remainder omitted)

Error messages (under valgrind)

  destroying a MyClass
  ==23254== Invalid free() / delete / delete[]
  ==23254==    at 0x4020CC7: operator delete(void*) (vg_replace_malloc.c:244)
  ==23254==    by 0x8048BAE: void boost::checked_delete<int>(int*) (checked_delete.hpp:34)
  ==23254==    by 0x8048C95: boost::detail::sp_counted_impl_p<int>::dispose() (sp_counted_impl.hpp:79)
  ==23254==    by 0x8048A4F: boost::detail::sp_counted_base::release() (sp_counted_base_gcc_x86.hpp:145)
  ==23254==    by 0x8048A79: boost::detail::shared_count::~shared_count() (shared_count.hpp:205)
  ==23254==    by 0x8048A95: boost::shared_ptr<int>::~shared_ptr() (shared_ptr.hpp:131)
  ==23254==    by 0x8048CD3: MyClass::~MyClass() (frag-pass-by-ref_03.cc:21)
  ==23254==    by 0x8048970: main (frag-pass-by-ref_03.cc:31)
  ==23254==  Address 0xBE8944FC is on thread 1's stack
  (error summary omitted)

8< -------------------------------------------

#include <iostream>                // standard io
#include <boost/shared_ptr.hpp>    // Boost shared pointer

class MyClass
{
public:
  MyClass (int& i)                 // & indicates pass-by-reference
    : d_int(&i) { }                // & is address-of operator
  ~MyClass() { std::cout << "destroying a MyClass" << std::endl; }
private:
  boost::shared_ptr<int> d_int;    // shared pointer FAILS
  // int*                d_int;    // raw pointer works
};

int main()
{
  int myint(2);                    // simple integer
  MyClass myclass(myint);          // constructor call
  return 0;
}

------------------------------------------- >8

---
Robbie Morrison
PhD student -- policy-oriented energy system simulation
Institute for Energy Engineering (IET)
Technical University of Berlin (TU-Berlin), Germany
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