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+/*
+ *          Copyright Andrey Semashev 2007 - 2014.
+ * 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   timer.hpp
+ * \author Andrey Semashev
+ * \date   02.12.2007
+ *
+ * The header contains implementation of a stop watch attribute.
+ */
+
+#ifndef BOOST_LOG_ATTRIBUTES_TIMER_HPP_INCLUDED_
+#define BOOST_LOG_ATTRIBUTES_TIMER_HPP_INCLUDED_
+
+#include <boost/log/detail/config.hpp>
+#include <boost/log/attributes/attribute.hpp>
+#include <boost/log/attributes/attribute_cast.hpp>
+#include <boost/log/attributes/time_traits.hpp>
+#include <boost/log/detail/header.hpp>
+
+#ifdef BOOST_HAS_PRAGMA_ONCE
+#pragma once
+#endif
+
+namespace boost {
+
+BOOST_LOG_OPEN_NAMESPACE
+
+namespace attributes {
+
+/*!
+ * \brief A class of an attribute that makes an attribute value of the time interval since construction
+ *
+ * The timer attribute calculates the time passed since its construction and returns it on value acquisition.
+ * The attribute value type is <tt>boost::posix_time::time_duration</tt>.
+ *
+ * On Windows platform there are two implementations of the attribute. The default one is more precise but
+ * a bit slower. This version uses <tt>QueryPerformanceFrequence</tt>/<tt>QueryPerformanceCounter</tt> API
+ * to calculate elapsed time.
+ *
+ * There are known problems with these functions when used with some CPUs, notably AMD Athlon with
+ * Cool'n'Quiet technology enabled. See the following links for more information and possible resolutions:
+ *
+ * http://support.microsoft.com/?scid=kb;en-us;895980
+ * http://support.microsoft.com/?id=896256
+ *
+ * In case if none of these solutions apply, you are free to define <tt>BOOST_LOG_NO_QUERY_PERFORMANCE_COUNTER</tt> macro to
+ * fall back to another implementation based on Boost.DateTime.
+ */
+class BOOST_LOG_API timer :
+    public attribute
+{
+public:
+    //! Attribute value type
+    typedef utc_time_traits::time_type::time_duration_type value_type;
+
+private:
+    //! Factory implementation
+    class BOOST_SYMBOL_VISIBLE impl;
+
+public:
+    /*!
+     * Constructor. Starts time counting.
+     */
+    timer();
+    /*!
+     * Constructor for casting support
+     */
+    explicit timer(cast_source const& source);
+};
+
+} // namespace attributes
+
+BOOST_LOG_CLOSE_NAMESPACE // namespace log
+
+} // namespace boost
+
+#include <boost/log/detail/footer.hpp>
+
+#endif // BOOST_LOG_ATTRIBUTES_TIMER_HPP_INCLUDED_