shared_from_this fails in a destructor

[nobody]

version: boost 1.30.0
library: smart pointers

I am using the boost::enable_shared_from_this base
class from the smart pointer library to implement
shared_from_this in my classes. I was amazed to find
this class, after hours of thashing trying even to
figure out the very problem it solves. So, first off,
thanks to the boosters.

My problem is that shared_from_this() throws
boost::bad_weak_ptr if called from my class's
destructor. Is this a design decision? a bug? am I
misunderstanding a class requirement?

The problem (if it is one...) is that
sp_counted_base::release() decrements use_count_ before
calling dispose(). Then when my class calls
shared_from_this from its destructor (via dispose()),
sp_counted_base::add_ref fails (use_count == 0) and
throws boost::bad_weak_ptr.

I would suggest either setting use_count_ after
dispose(), or clarifying in the docs that
shared_from_this can't be called from a destructor. 

It would also be handy to have an exception-less
version of share_from_this which justs returns a null
shared_ptr, kind of like how shared_ptr::get doesn't throw.

Thanks for any help. ... Michael Ost

PS: code looks something like this (warning:
uncompiled, untested!) ...

class T : public enable_shared_from_this {
public:
   T() {}
   ~T()
   {
      shared_ptr<T> ptr = shared_from_this(); 
      // trouble: exception, can't get a shared_ptr
   }
};

main()
{
   shared_ptr<T> ptr = shared_ptr(new T());
   ptr.reset();
}

[murgatroid]

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I submitted this as user murgatroid, email
most@museresearch.com. Somehow that didn't get recorded...?

[Peter Dimov]

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user_id=305912

This behavior is by design. Since the destructor will destroy 
the object, it is not safe to create a shared_ptr to it as it will 
become dangling once the destructor ends.

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