[boost] Shared_ptr "mini garbage collector"

From: Peter Dimov (pdimov_at_[hidden])
Date: 2003-01-07 10:39:36

I've added a simple mark and sweep "garbage collector" to
libs/smart_ptr/sp_debug_hooks.cpp that is able to detect unreachable objects
kept alive by shared_ptr cycles. At the moment it's more a debugging aid,
and doesn't attempt to free memory, athough it is possible to extend it to
do so. This is mainly a research project; if you think that it might have a
practical use let me know. :-)

Example: (compile with -DBOOST_ENABLE_SP_DEBUG_HOOKS, link with
sp_debug_hooks.cpp)

#include <boost/shared_ptr.hpp>
#include <iostream>

struct X
{
    boost::shared_ptr<X> p;
};

void report_unreachable_objects(); // in sp_debug_hooks.cpp

int main()
{
    boost::shared_ptr<X> p1(new X);
    boost::shared_ptr<X> p2(new X);

    p1->p = p2;
    p2->p = p1;

    report_unreachable_objects();
    std::cout << "--\n";

    p1.reset();

    report_unreachable_objects();
    std::cout << "--\n";

    p2.reset();

    report_unreachable_objects();
}

Output:

C:\Documents and Settings\pdimov\My Documents\Projects\testbed>a
--
--
Unreachable object at 0x3d2c78, 12 bytes long.
Unreachable object at 0x3d2cc0, 12 bytes long.
--
Peter Dimov
http://www.pdimov.com