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diff --git a/lib/asio/executor_work_guard.hpp b/lib/asio/executor_work_guard.hpp
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+//
+// executor_work_guard.hpp
+// ~~~~~~~~~~~~~~~~~
+//
+// Copyright (c) 2003-2018 Christopher M. Kohlhoff (chris at kohlhoff dot com)
+//
+// 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)
+//
+
+#ifndef ASIO_EXECUTOR_WORK_GUARD_HPP
+#define ASIO_EXECUTOR_WORK_GUARD_HPP
+
+#if defined(_MSC_VER) && (_MSC_VER >= 1200)
+# pragma once
+#endif // defined(_MSC_VER) && (_MSC_VER >= 1200)
+
+#include "asio/detail/config.hpp"
+#include "asio/associated_executor.hpp"
+#include "asio/detail/type_traits.hpp"
+#include "asio/is_executor.hpp"
+
+#include "asio/detail/push_options.hpp"
+
+namespace asio {
+
+/// An object of type @c executor_work_guard controls ownership of executor work
+/// within a scope.
+template <typename Executor>
+class executor_work_guard
+{
+public:
+  /// The underlying executor type.
+  typedef Executor executor_type;
+
+  /// Constructs a @c executor_work_guard object for the specified executor.
+  /**
+   * Stores a copy of @c e and calls <tt>on_work_started()</tt> on it.
+   */
+  explicit executor_work_guard(const executor_type& e) ASIO_NOEXCEPT
+    : executor_(e),
+      owns_(true)
+  {
+    executor_.on_work_started();
+  }
+
+  /// Copy constructor.
+  executor_work_guard(const executor_work_guard& other) ASIO_NOEXCEPT
+    : executor_(other.executor_),
+      owns_(other.owns_)
+  {
+    if (owns_)
+      executor_.on_work_started();
+  }
+
+#if defined(ASIO_HAS_MOVE) || defined(GENERATING_DOCUMENTATION)
+  /// Move constructor.
+  executor_work_guard(executor_work_guard&& other)
+    : executor_(ASIO_MOVE_CAST(Executor)(other.executor_)),
+      owns_(other.owns_)
+  {
+    other.owns_ = false;
+  }
+#endif //  defined(ASIO_HAS_MOVE) || defined(GENERATING_DOCUMENTATION)
+
+  /// Destructor.
+  /**
+   * Unless the object has already been reset, or is in a moved-from state,
+   * calls <tt>on_work_finished()</tt> on the stored executor.
+   */
+  ~executor_work_guard()
+  {
+    if (owns_)
+      executor_.on_work_finished();
+  }
+
+  /// Obtain the associated executor.
+  executor_type get_executor() const ASIO_NOEXCEPT
+  {
+    return executor_;
+  }
+
+  /// Whether the executor_work_guard object owns some outstanding work.
+  bool owns_work() const ASIO_NOEXCEPT
+  {
+    return owns_;
+  }
+
+  /// Indicate that the work is no longer outstanding.
+  /*
+   * Unless the object has already been reset, or is in a moved-from state,
+   * calls <tt>on_work_finished()</tt> on the stored executor.
+   */
+  void reset() ASIO_NOEXCEPT
+  {
+    if (owns_)
+    {
+      executor_.on_work_finished();
+      owns_ = false;
+    }
+  }
+
+private:
+  // Disallow assignment.
+  executor_work_guard& operator=(const executor_work_guard&);
+
+  executor_type executor_;
+  bool owns_;
+};
+
+/// Create an @ref executor_work_guard object.
+template <typename Executor>
+inline executor_work_guard<Executor> make_work_guard(const Executor& ex,
+    typename enable_if<is_executor<Executor>::value>::type* = 0)
+{
+  return executor_work_guard<Executor>(ex);
+}
+
+/// Create an @ref executor_work_guard object.
+template <typename ExecutionContext>
+inline executor_work_guard<typename ExecutionContext::executor_type>
+make_work_guard(ExecutionContext& ctx,
+    typename enable_if<
+      is_convertible<ExecutionContext&, execution_context&>::value>::type* = 0)
+{
+  return executor_work_guard<typename ExecutionContext::executor_type>(
+      ctx.get_executor());
+}
+
+/// Create an @ref executor_work_guard object.
+template <typename T>
+inline executor_work_guard<typename associated_executor<T>::type>
+make_work_guard(const T& t,
+    typename enable_if<!is_executor<T>::value &&
+      !is_convertible<T&, execution_context&>::value>::type* = 0)
+{
+  return executor_work_guard<typename associated_executor<T>::type>(
+      associated_executor<T>::get(t));
+}
+
+/// Create an @ref executor_work_guard object.
+template <typename T, typename Executor>
+inline executor_work_guard<typename associated_executor<T, Executor>::type>
+make_work_guard(const T& t, const Executor& ex,
+    typename enable_if<is_executor<Executor>::value>::type* = 0)
+{
+  return executor_work_guard<typename associated_executor<T, Executor>::type>(
+      associated_executor<T, Executor>::get(t, ex));
+}
+
+/// Create an @ref executor_work_guard object.
+template <typename T, typename ExecutionContext>
+inline executor_work_guard<typename associated_executor<T,
+  typename ExecutionContext::executor_type>::type>
+make_work_guard(const T& t, ExecutionContext& ctx,
+    typename enable_if<!is_executor<T>::value &&
+      !is_convertible<T&, execution_context&>::value &&
+      is_convertible<ExecutionContext&, execution_context&>::value>::type* = 0)
+{
+  return executor_work_guard<typename associated_executor<T,
+    typename ExecutionContext::executor_type>::type>(
+      associated_executor<T, typename ExecutionContext::executor_type>::get(
+        t, ctx.get_executor()));
+}
+
+} // namespace asio
+
+#include "asio/detail/pop_options.hpp"
+
+#endif // ASIO_EXECUTOR_WORK_GUARD_HPP