Ticket #1696: enable_shared_from_this_v3.patch

boost/enable_shared_from_this.hpp

@@ -23 +23 @@
 
 template<class T> class enable_shared_from_this
 {
+// dynamic cast to template type doesn't work in constructor, so we have
+// to use lazy initialization
+    void init_internal_shared_once() const
+    {
+        if(_owned == false && _internal_shared_this == 0)
+        {
+            _internal_shared_this = shared_ptr<T>(dynamic_cast<T *>(const_cast<enable_shared_from_this*>(this)),
+                detail::deleter_wrapper(), detail::ignore_enable_shared_from_this_tag());
+            BOOST_ASSERT(_internal_shared_this.get() == this);
+            _internal_weak_this = _internal_shared_this;
+        }
+    }
+
+    typedef T _internal_element_type; // for bcc 5.5.1
+    mutable shared_ptr<_internal_element_type> _internal_shared_this;
+    mutable weak_ptr<_internal_element_type> _internal_weak_this;
+    mutable bool _owned;
 protected:
 
-    enable_shared_from_this()
+    enable_shared_from_this():
+      _owned(false)
     {
     }
 
@@ -38 +56 @@
         return *this;
     }
 
-    ~enable_shared_from_this()
+// virtual destructor because we need a vtable for dynamic_cast from base to derived to work
+    virtual ~enable_shared_from_this()
     {
+// make sure no dangling shared_ptr objects were created by the
+// user calling shared_from_this() but never passing ownership of the object
+// to a shared_ptr.
+        BOOST_ASSERT(owned() || _internal_shared_this.unique() || _internal_shared_this == 0);
     }
 
 public:
 
     shared_ptr<T> shared_from_this()
     {
+        init_internal_shared_once();
         shared_ptr<T> p(_internal_weak_this);
         BOOST_ASSERT(p.get() == this);
         return p;
@@ -53 +77 @@
 
     shared_ptr<T const> shared_from_this() const
     {
+        init_internal_shared_once();
         shared_ptr<T const> p(_internal_weak_this);
         BOOST_ASSERT(p.get() == this);
         return p;
     }
 
-//  Note: No, you don't need to initialize _internal_weak_this
-//
-//  Please read the documentation, not the code
-//
-//  http://www.boost.org/libs/smart_ptr/enable_shared_from_this.html
+    bool owned() const
+    {
+        return _owned;
+    }
 
-    typedef T _internal_element_type; // for bcc 5.5.1
-    mutable weak_ptr<_internal_element_type> _internal_weak_this;
+    template<typename U>
+    void _internal_accept_owner(shared_ptr<U> &owner) const
+    {
+        init_internal_shared_once();
+        get_deleter<detail::deleter_wrapper>(_internal_shared_this)->set_deleter(owner);
+        owner = _internal_shared_this;
+        _internal_shared_this.reset();
+        _owned = true;
+    }
 };
 
 } // namespace boost

boost/shared_ptr.hpp

@@ -48 +48 @@
 namespace boost
 {
 
+template<class T> class shared_ptr;
 template<class T> class weak_ptr;
 template<class T> class enable_shared_from_this;
 
@@ -90 +91 @@
 
 // enable_shared_from_this support
 
-template<class T, class Y> void sp_enable_shared_from_this( shared_count const & pn, boost::enable_shared_from_this<T> const * pe, Y const * px )
+struct ignore_enable_shared_from_this_tag {};
+
+template<class T, class Y> void sp_enable_shared_from_this( boost::shared_ptr<Y> * ptr, boost::enable_shared_from_this<T> const * pe )
 {
-    if(pe != 0) pe->_internal_weak_this._internal_assign(const_cast<Y*>(px), pn);
+    if(pe != 0)
+    {
+        pe->_internal_accept_owner(*ptr);
 }
+}
 
 #ifdef _MANAGED
 
@@ -104 +110 @@
     template<class T> sp_any_pointer( T* ) {}
 };
 
-inline void sp_enable_shared_from_this( shared_count const & /*pn*/, sp_any_pointer, sp_any_pointer )
+inline void sp_enable_shared_from_this( sp_any_pointer, sp_any_pointer )
 {
 }
 
@@ -115 +121 @@
 # pragma set woff 3506
 #endif
 
-inline void sp_enable_shared_from_this( shared_count const & /*pn*/, ... )
+inline void sp_enable_shared_from_this( ... )
 {
 }
 
@@ -172 +178 @@
     template<class Y>
     explicit shared_ptr( Y * p ): px( p ), pn( p ) // Y must be complete
     {
-        boost::detail::sp_enable_shared_from_this( pn, p, p );
+        boost::detail::sp_enable_shared_from_this( this, p );
     }
 
     //
@@ -183 +189 @@
 
     template<class Y, class D> shared_ptr(Y * p, D d): px(p), pn(p, d)
     {
-        boost::detail::sp_enable_shared_from_this( pn, p, p );
+        boost::detail::sp_enable_shared_from_this( this, p );
     }
 
     // As above, but with allocator. A's copy constructor shall not throw.
 
     template<class Y, class D, class A> shared_ptr( Y * p, D d, A a ): px( p ), pn( p, d, a )
     {
-        boost::detail::sp_enable_shared_from_this( pn, p, p );
+        boost::detail::sp_enable_shared_from_this( this, p );
     }
 
 //  generated copy constructor, assignment, destructor are fine...
@@ -253 +259 @@
         }
     }
 
+    // constructor that doesn't trigger enable_shared_from_this code, needed
+    // for enable_shared_from_this internal implementation
+    template<class Y, class D> shared_ptr(Y * p, D d, detail::ignore_enable_shared_from_this_tag tag):
+      px(p), pn(p, d)
+    {}
+
 #ifndef BOOST_NO_AUTO_PTR
 
     template<class Y>
@@ -260 +272 @@
     {
         Y * tmp = r.get();
         pn = boost::detail::shared_count(r);
-        boost::detail::sp_enable_shared_from_this( pn, tmp, tmp );
+        boost::detail::sp_enable_shared_from_this( this, tmp );
     }
 
 #if !defined( BOOST_NO_SFINAE ) && !defined( BOOST_NO_TEMPLATE_PARTIAL_SPECIALIZATION )
@@ -270 +282 @@
     {
         typename Ap::element_type * tmp = r.get();
         pn = boost::detail::shared_count( r );
-        boost::detail::sp_enable_shared_from_this( pn, tmp, tmp );
+        boost::detail::sp_enable_shared_from_this( this, tmp );
     }
 
 
@@ -597 +609 @@
 
 // get_deleter
 
+namespace detail
+{
 #if ( defined(__GNUC__) && BOOST_WORKAROUND(__GNUC__, < 3) ) || \
     ( defined(__EDG_VERSION__) && BOOST_WORKAROUND(__EDG_VERSION__, <= 238) ) || \
     ( defined(__HP_aCC) && BOOST_WORKAROUND(__HP_aCC, <= 33500) )
@@ -604 +618 @@
 // g++ 2.9x doesn't allow static_cast<X const *>(void *)
 // apparently EDG 2.38 and HP aCC A.03.35 also don't accept it
 
-template<class D, class T> D * get_deleter(shared_ptr<T> const & p)
+template<class D, class T> D * basic_get_deleter(shared_ptr<T> const & p)
 {
     void const * q = p._internal_get_deleter(BOOST_SP_TYPEID(D));
     return const_cast<D *>(static_cast<D const *>(q));
@@ -612 +626 @@
 
 #else
 
-template<class D, class T> D * get_deleter(shared_ptr<T> const & p)
+template<class D, class T> D * basic_get_deleter(shared_ptr<T> const & p)
 {
     return static_cast<D *>(p._internal_get_deleter(BOOST_SP_TYPEID(D)));
 }
 
 #endif
 
+class deleter_wrapper
+{
+    shared_ptr<const void> _deleter;
+public:
+    deleter_wrapper()
+    {}
+    void set_deleter(const shared_ptr<const void> &deleter)
+    {
+        _deleter = deleter;
+    }
+    void operator()(const void *)
+    {
+        BOOST_ASSERT(_deleter.unique());
+        _deleter.reset();
+    }
+    template<typename D>
+    D* get_deleter() const
+    {
+        return boost::detail::basic_get_deleter<D>(_deleter);
+    }
+};
+
+} // namespace detail
+
+template<class D, class T> D * get_deleter(shared_ptr<T> const & p)
+{
+    D *del = detail::basic_get_deleter<D>(p);
+    if(del == 0)
+    {
+        detail::deleter_wrapper *del_wrapper = detail::basic_get_deleter<detail::deleter_wrapper>(p);
+        if(del_wrapper) del = del_wrapper->get_deleter<D>();
+    }
+    return del;
+}
+
 } // namespace boost
 
 #ifdef BOOST_MSVC