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include/boost/smart_ptr/intrusive_ref_counter.hpp

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+/*
+ *          Copyright Andrey Semashev 2007 - 2013.
+ * Distributed under the Boost Software License, Version 1.0.
+ *    (See accompanying file LICENSE_1_0.txt or copy at
+ *          http://www.boost.org/LICENSE_1_0.txt)
+ */
+/*!
+ * \file   intrusive_ref_counter.hpp
+ * \author Andrey Semashev
+ * \date   12.03.2009
+ *
+ * This header contains a reference counter class for \c intrusive_ptr.
+ */
+
+#ifndef BOOST_SMART_PTR_INTRUSIVE_REF_COUNTER_HPP_INCLUDED_
+#define BOOST_SMART_PTR_INTRUSIVE_REF_COUNTER_HPP_INCLUDED_
+
+#include <boost/smart_ptr/detail/atomic_count.hpp>
+#include <boost/config.hpp>
+
+#ifdef BOOST_HAS_PRAGMA_ONCE
+#pragma once
+#endif
+
+#if defined(_MSC_VER)
+#pragma warning(push)
+// This is a bogus MSVC warning, which is flagged by friend declarations of intrusive_ptr_add_ref and intrusive_ptr_release in intrusive_ref_counter:
+// 'name' : the inline specifier cannot be used when a friend declaration refers to a specialization of a function template
+// Note that there is no inline specifier in the declarations.
+#pragma warning(disable: 4396)
+#endif
+
+namespace boost {
+
+namespace sp_adl_block {
+
+/*!
+ * \brief Thread unsafe reference counter policy for \c intrusive_ref_counter
+ *
+ * The policy instructs the \c intrusive_ref_counter base class to implement
+ * a reference counter suitable for single threaded use only. Pointers to the same
+ * object with this kind of reference counter must not be used by different threads.
+ */
+struct thread_unsafe_counter
+{
+    typedef unsigned int type;
+
+    static unsigned int load(unsigned int const& counter) noexcept
+    {
+        return counter;
+    }
+
+    static void increment(unsigned int& counter) noexcept
+    {
+        ++counter;
+    }
+
+    static unsigned int decrement(unsigned int& counter) noexcept
+    {
+        return --counter;
+    }
+};
+
+/*!
+ * \brief Thread safe reference counter policy for \c intrusive_ref_counter
+ *
+ * The policy instructs the \c intrusive_ref_counter base class to implement
+ * a thread-safe reference counter, if the target platform supports multithreading.
+ */
+struct thread_safe_counter
+{
+    typedef boost::detail::atomic_count type;
+
+    static unsigned int load(boost::detail::atomic_count const& counter) noexcept
+    {
+        return static_cast< unsigned int >(static_cast< long >(counter));
+    }
+
+    static void increment(boost::detail::atomic_count& counter) noexcept
+    {
+        ++counter;
+    }
+
+    static unsigned int decrement(boost::detail::atomic_count& counter) noexcept
+    {
+        return static_cast< unsigned int >(--counter);
+    }
+};
+
+template< typename DerivedT, typename CounterPolicyT = thread_safe_counter >
+class intrusive_ref_counter;
+
+template< typename DerivedT, typename CounterPolicyT >
+void intrusive_ptr_add_ref(const intrusive_ref_counter< DerivedT, CounterPolicyT >* p) noexcept;
+template< typename DerivedT, typename CounterPolicyT >
+void intrusive_ptr_release(const intrusive_ref_counter< DerivedT, CounterPolicyT >* p) noexcept;
+
+/*!
+ * \brief A reference counter base class
+ *
+ * This base class can be used with user-defined classes to add support
+ * for \c intrusive_ptr. The class contains a reference counter defined by the \c CounterPolicyT.
+ * Upon releasing the last \c intrusive_ptr referencing the object
+ * derived from the \c intrusive_ref_counter class, operator \c delete
+ * is automatically called on the pointer to the object.
+ *
+ * The other template parameter, \c DerivedT, is the user's class that derives from \c intrusive_ref_counter.
+ */
+template< typename DerivedT, typename CounterPolicyT >
+class intrusive_ref_counter
+{
+private:
+    //! Reference counter type
+    typedef typename CounterPolicyT::type counter_type;
+    //! Reference counter
+    mutable counter_type m_ref_counter;
+
+public:
+    /*!
+     * Default constructor
+     *
+     * \post <tt>use_count() == 0</tt>
+     */
+    intrusive_ref_counter() noexcept : m_ref_counter(0)
+    {
+    }
+
+    /*!
+     * Copy constructor
+     *
+     * \post <tt>use_count() == 0</tt>
+     */
+    intrusive_ref_counter(intrusive_ref_counter const&) noexcept : m_ref_counter(0)
+    {
+    }
+
+    /*!
+     * Assignment
+     *
+     * \post The reference counter is not modified after assignment
+     */
+    intrusive_ref_counter& operator= (intrusive_ref_counter const&) noexcept { return *this; }
+
+    /*!
+     * \return The reference counter
+     */
+    unsigned int use_count() const noexcept
+    {
+        return CounterPolicyT::load(m_ref_counter);
+    }
+
+protected:
+    /*!
+     * Destructor
+     */
+    BOOST_DEFAULTED_FUNCTION(~intrusive_ref_counter(), {})
+
+    friend void intrusive_ptr_add_ref< DerivedT, CounterPolicyT >(const intrusive_ref_counter< DerivedT, CounterPolicyT >* p) noexcept;
+    friend void intrusive_ptr_release< DerivedT, CounterPolicyT >(const intrusive_ref_counter< DerivedT, CounterPolicyT >* p) noexcept;
+};
+
+template< typename DerivedT, typename CounterPolicyT >
+inline void intrusive_ptr_add_ref(const intrusive_ref_counter< DerivedT, CounterPolicyT >* p) noexcept
+{
+    CounterPolicyT::increment(p->m_ref_counter);
+}
+
+template< typename DerivedT, typename CounterPolicyT >
+inline void intrusive_ptr_release(const intrusive_ref_counter< DerivedT, CounterPolicyT >* p) noexcept
+{
+    if (CounterPolicyT::decrement(p->m_ref_counter) == 0)
+        delete static_cast< const DerivedT* >(p);
+}
+
+} // namespace sp_adl_block
+
+using sp_adl_block::intrusive_ref_counter;
+using sp_adl_block::thread_unsafe_counter;
+using sp_adl_block::thread_safe_counter;
+
+} // namespace boost
+
+#if defined(_MSC_VER)
+#pragma warning(pop)
+#endif
+
+#endif // BOOST_SMART_PTR_INTRUSIVE_REF_COUNTER_HPP_INCLUDED_