Reduce enable_shared_from_this overhead

[SVN r44724]

include/boost/detail/shared_count.hpp

@@ -220,6 +220,18 @@ public:
         if( pi_ != 0 ) pi_->add_ref_copy();
     }
 
+#if defined( BOOST_HAS_RVALUE_REFS )
+
+    shared_count(shared_count && r): pi_(r.pi_) // nothrow
+#if defined(BOOST_SP_ENABLE_DEBUG_HOOKS)
+        , id_(shared_count_id)
+#endif
+    {
+        r.pi_ = 0;
+    }
+
+#endif
+
     explicit shared_count(weak_count const & r); // throws bad_weak_ptr when r.use_count() == 0
     shared_count( weak_count const & r, sp_nothrow_tag ); // constructs an empty *this when r.use_count() == 0
 

include/boost/enable_shared_from_this.hpp

@@ -13,7 +13,7 @@
 //  http://www.boost.org/libs/smart_ptr/enable_shared_from_this.html
 //
 
-#include <boost/weak_ptr.hpp>
+#include <boost/detail/shared_count.hpp>
 #include <boost/shared_ptr.hpp>
 #include <boost/assert.hpp>
 #include <boost/config.hpp>
@@ -32,7 +32,7 @@ template<class T> class enable_shared_from_this
             T * p = dynamic_cast<T *>(const_cast<enable_shared_from_this*>(this));
             _internal_shared_this = shared_ptr<T>( p, detail::sp_deleter_wrapper() );
             BOOST_ASSERT(_internal_shared_this.get() == this);
-            _internal_weak_this = _internal_shared_this;
+            _internal_weak_count = _internal_shared_this.get_shared_count();
         }
     }
 
@@ -43,7 +43,7 @@ template<class T> class enable_shared_from_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 detail::weak_count _internal_weak_count;
     mutable bool _owned;
 
 protected:
@@ -77,17 +77,15 @@ 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;
+        T * p = dynamic_cast<T *>(this);
+        return shared_ptr<T>( detail::shared_count( _internal_weak_count ), p );
     }
 
     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;
+        T const * p = dynamic_cast<T const *>(this);
+        return shared_ptr<T const>( detail::shared_count( _internal_weak_count ), p );
     }
 
     template<typename U>
@@ -97,8 +95,7 @@ public:
         {
             if( !_internal_shared_this )
             {
-                T * p = dynamic_cast<T *>(const_cast<enable_shared_from_this*>(this));
-                _internal_weak_this = shared_ptr<T>(owner, p);
+                _internal_weak_count = owner.get_shared_count();
             }else
             {
                 BOOST_ASSERT(owner.unique()); // no weak_ptrs to owner should exist either, but there's no way to check that

include/boost/shared_ptr.hpp

@@ -228,6 +228,11 @@ public:
     {
     }
 
+    template<class Y>
+    shared_ptr(detail::shared_count const & c, Y * p): px(p), pn(c) // never throws
+    {
+    }
+
     // aliasing
     template< class Y >
     shared_ptr( shared_ptr<Y> const & r, T * p ): px( p ), pn( r.pn ) // never throws
@@ -341,6 +346,11 @@ public:
         r.px = 0;
     }
 
+    template<class Y>
+    shared_ptr(detail::shared_count && c, Y * p): px(p), pn( static_cast< detail::shared_count && >( c ) ) // never throws
+    {
+    }
+
     shared_ptr & operator=( shared_ptr && r ) // never throws
     {
         this_type( static_cast< shared_ptr && >( r ) ).swap( *this );
@@ -467,6 +477,11 @@ public:
         pn.swap(other.pn);
     }
 
+    detail::shared_count const & get_shared_count() const // never throws
+    {
+        return pn;
+    }
+
     template<class Y> bool _internal_less(shared_ptr<Y> const & rhs) const
     {
         return pn < rhs.pn;