Use executor_work_guard in composed operations:

fix #1076

As per Asio and Networking TS requirements, composed operations must
maintain an object of type executor_work_guard for the executor associated
with the I/O object, for the lifetime of the asynchronous operation.

This is in addition to the requirement for maintaining an object of type
executor_work_guard for the executor associated with the handler.

test/extras/include/boost/beast/test/stream.hpp

@@ -19,6 +19,7 @@
 #include <boost/beast/test/fail_counter.hpp>
 #include <boost/asio/async_result.hpp>
 #include <boost/asio/buffer.hpp>
+#include <boost/asio/executor_work_guard.hpp>
 #include <boost/asio/io_context.hpp>
 #include <boost/asio/post.hpp>
 #include <boost/assert.hpp>
@@ -697,9 +698,8 @@ class stream::read_op_impl : public stream::read_op
         state& s_;
         Buffers b_;
         Handler h_;
-        boost::optional<
-            boost::asio::executor_work_guard<
-                boost::asio::io_context::executor_type>> work_;
+        boost::asio::executor_work_guard<
+            boost::asio::io_context::executor_type> work_;
 
     public:
         lambda(lambda&&) = default;
@@ -720,7 +720,7 @@ class stream::read_op_impl : public stream::read_op
             boost::asio::post(
                 s_.ioc.get_executor(),
                 std::move(*this));
-            work_ = boost::none;
+            work_.reset();
         }
 
         void

test/extras/include/boost/beast/test/yield_to.hpp

@@ -10,9 +10,9 @@
 #ifndef BOOST_BEAST_TEST_YIELD_TO_HPP
 #define BOOST_BEAST_TEST_YIELD_TO_HPP
 
+#include <boost/asio/executor_work_guard.hpp>
 #include <boost/asio/io_context.hpp>
 #include <boost/asio/spawn.hpp>
-#include <boost/optional.hpp>
 #include <condition_variable>
 #include <functional>
 #include <mutex>
@@ -35,9 +35,8 @@ protected:
     boost::asio::io_context ioc_;
 
 private:
-    boost::optional<
-        boost::asio::executor_work_guard<
-            boost::asio::io_context::executor_type>> work_;
+    boost::asio::executor_work_guard<
+        boost::asio::io_context::executor_type> work_;
     std::vector<std::thread> threads_;
     std::mutex m_;
     std::condition_variable cv_;
@@ -60,7 +59,7 @@ public:
 
     ~enable_yield_to()
     {
-        work_ = boost::none;
+        work_.reset();
         for(auto& t : threads_)
             t.join();
     }