[Boost-users] boost::bind - using boost::weak_ptr

From: Remigiusz ¯ukowski (wiewior_at_[hidden])
Date: 2007-01-04 06:36:35

hello,

Callback mechanism defined by boost::function and by means boost::bind 
instead of using callback virtual class is very comfortable, but has one big 
shortcoming: using callback class, passing object can be stored as weak_ptr 
and if weak_ptr is invalid the callback can be automatically unregistered. 
I've tried to implement such behaviour with boost::function and boost::bind 
with some helper class holding weak_ptr:

template<typename T> class my_wptr
{
    boost::weak_ptr<T> m_wptr;
    constructors etc...
};

and two helper functions:

template<typename T> T* get_pointer( my_wptr &_wptr )
{
     boost::shared_ptr<T> sptr = _wptr.m_wptr.lock();
    if( !sptr )
        throw some_exception;
    return _wptr.get();
}

and

template<typename T> my_wptr<T> wptr_from( boost::weak_ptr<T> &_sptr )
{
    return my_wptr( _sptr );
}

now I can use standard shared_ptr version:
boost::function<void()> f1 = boost::bind( &class::method, 
some_shared_ptr );
or my version holding weak_ptr:
boost::function<void()> f2 = boost::bind( &class::method, wptr_from( 
some_weak_ptr ));

This works, but is unsafe - after get_pointer succesfully returns pointer to 
the object, the object is unlocked and can be deleted during class::method 
execution. Can anyone help me solving this problem ?

regards

Remigiusz Zukowski, Poland

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