diff --git a/asio/include/asio/associated_executor.hpp b/asio/include/asio/associated_executor.hpp
index 65e01a3..1219890 100644
--- a/asio/include/asio/associated_executor.hpp
+++ b/asio/include/asio/associated_executor.hpp
@@ -17,8 +17,8 @@
 
 #include "asio/detail/config.hpp"
 #include "asio/detail/type_traits.hpp"
+#include "asio/execution_context.hpp"
 #include "asio/is_executor.hpp"
-#include "asio/system_executor.hpp"
 
 #include "asio/detail/push_options.hpp"
 
@@ -75,7 +75,7 @@
  * @li Provide a noexcept static member function named @c get, callable as @c
  * get(t,e) and with return type @c type.
  */
-template <typename T, typename Executor = system_executor>
+template <typename T, typename Executor>
 struct associated_executor
 {
   /// If @c T has a nested type @c executor_type, <tt>T::executor_type</tt>.
@@ -88,8 +88,7 @@
 
   /// If @c T has a nested type @c executor_type, returns
   /// <tt>t.get_executor()</tt>. Otherwise returns @c ex.
-  static type get(const T& t,
-      const Executor& ex = Executor()) ASIO_NOEXCEPT
+  static type get(const T& t, const Executor& ex) ASIO_NOEXCEPT
   {
     return detail::associated_executor_impl<T, Executor>::get(t, ex);
   }
@@ -97,17 +96,6 @@
 
 /// Helper function to obtain an object's associated executor.
 /**
- * @returns <tt>associated_executor<T>::get(t)</tt>
- */
-template <typename T>
-inline typename associated_executor<T>::type
-get_associated_executor(const T& t) ASIO_NOEXCEPT
-{
-  return associated_executor<T>::get(t);
-}
-
-/// Helper function to obtain an object's associated executor.
-/**
  * @returns <tt>associated_executor<T, Executor>::get(t, ex)</tt>
  */
 template <typename T, typename Executor>
@@ -137,7 +125,7 @@
 
 #if defined(ASIO_HAS_ALIAS_TEMPLATES)
 
-template <typename T, typename Executor = system_executor>
+template <typename T, typename Executor>
 using associated_executor_t = typename associated_executor<T, Executor>::type;
 
 #endif // defined(ASIO_HAS_ALIAS_TEMPLATES)
diff --git a/asio/include/asio/detail/completion_handler.hpp b/asio/include/asio/detail/completion_handler.hpp
index ce8e9b7..328feae 100644
--- a/asio/include/asio/detail/completion_handler.hpp
+++ b/asio/include/asio/detail/completion_handler.hpp
@@ -21,6 +21,7 @@
 #include "asio/detail/handler_work.hpp"
 #include "asio/detail/memory.hpp"
 #include "asio/detail/operation.hpp"
+#include "asio/system_executor.hpp"
 
 #include "asio/detail/push_options.hpp"
 
@@ -37,7 +38,7 @@
     : operation(&completion_handler::do_complete),
       handler_(ASIO_MOVE_CAST(Handler)(h))
   {
-    handler_work<Handler>::start(handler_);
+    handler_work<Handler, system_executor>::start(handler_, system_executor());
   }
 
   static void do_complete(void* owner, operation* base,
@@ -47,7 +48,7 @@
     // Take ownership of the handler object.
     completion_handler* h(static_cast<completion_handler*>(base));
     ptr p = { asio::detail::addressof(h->handler_), h, h };
-    handler_work<Handler> w(h->handler_);
+    handler_work<Handler, system_executor> w(h->handler_);
 
     ASIO_HANDLER_COMPLETION((*h));
 
diff --git a/asio/include/asio/detail/dev_poll_reactor.hpp b/asio/include/asio/detail/dev_poll_reactor.hpp
index 0d62153..6f89d49 100644
--- a/asio/include/asio/detail/dev_poll_reactor.hpp
+++ b/asio/include/asio/detail/dev_poll_reactor.hpp
@@ -84,10 +84,7 @@
       per_descriptor_data& source_descriptor_data);
 
   // Post a reactor operation for immediate completion.
-  void post_immediate_completion(reactor_op* op, bool is_continuation)
-  {
-    scheduler_.post_immediate_completion(op, is_continuation);
-  }
+  void post_immediate_completion(reactor_op* op, bool is_continuation);
 
   // Start a new operation. The reactor operation will be performed when the
   // given descriptor is flagged as ready, or an error has occurred.
diff --git a/asio/include/asio/detail/epoll_reactor.hpp b/asio/include/asio/detail/epoll_reactor.hpp
index 032fc85..79b2971 100644
--- a/asio/include/asio/detail/epoll_reactor.hpp
+++ b/asio/include/asio/detail/epoll_reactor.hpp
@@ -114,10 +114,7 @@
       per_descriptor_data& source_descriptor_data);
 
   // Post a reactor operation for immediate completion.
-  void post_immediate_completion(reactor_op* op, bool is_continuation)
-  {
-    scheduler_.post_immediate_completion(op, is_continuation);
-  }
+  void post_immediate_completion(reactor_op* op, bool is_continuation);
 
   // Start a new operation. The reactor operation will be performed when the
   // given descriptor is flagged as ready, or an error has occurred.
diff --git a/asio/include/asio/detail/handler_work.hpp b/asio/include/asio/detail/handler_work.hpp
index 9be218c..bd514c2 100644
--- a/asio/include/asio/detail/handler_work.hpp
+++ b/asio/include/asio/detail/handler_work.hpp
@@ -18,6 +18,7 @@
 #include "asio/detail/config.hpp"
 #include "asio/associated_executor.hpp"
 #include "asio/detail/handler_invoke_helpers.hpp"
+#include "asio/system_executor.hpp"
 
 #include "asio/detail/push_options.hpp"
 
@@ -28,7 +29,7 @@
 // through either the new executors framework or the old invocaton hook. The
 // primary template uses the new executors framework.
 template <typename Handler,
-    typename IoExecutor = system_executor, typename HandlerExecutor
+    typename IoExecutor, typename HandlerExecutor
       = typename associated_executor<Handler, IoExecutor>::type>
 class handler_work
 {
@@ -45,12 +46,6 @@
   {
   }
 
-  static void start(Handler& handler) ASIO_NOEXCEPT
-  {
-    HandlerExecutor ex(asio::get_associated_executor(handler));
-    ex.on_work_started();
-  }
-
   static void start(Handler& handler,
       const IoExecutor& io_ex) ASIO_NOEXCEPT
   {
@@ -90,7 +85,7 @@
 {
 public:
   explicit handler_work(Handler&) ASIO_NOEXCEPT {}
-  static void start(Handler&) ASIO_NOEXCEPT {}
+  static void start(Handler&, const system_executor&) ASIO_NOEXCEPT {}
   ~handler_work() {}
 
   template <typename Function>
diff --git a/asio/include/asio/detail/impl/dev_poll_reactor.hpp b/asio/include/asio/detail/impl/dev_poll_reactor.hpp
index 31cd719..107a9eb 100644
--- a/asio/include/asio/detail/impl/dev_poll_reactor.hpp
+++ b/asio/include/asio/detail/impl/dev_poll_reactor.hpp
@@ -19,11 +19,19 @@
 
 #if defined(ASIO_HAS_DEV_POLL)
 
+#include "asio/detail/scheduler.hpp"
+
 #include "asio/detail/push_options.hpp"
 
 namespace asio {
 namespace detail {
 
+inline void dev_poll_reactor::post_immediate_completion(
+    reactor_op* op, bool is_continuation)
+{
+  scheduler_.post_immediate_completion(op, is_continuation);
+}
+
 template <typename Time_Traits>
 void dev_poll_reactor::add_timer_queue(timer_queue<Time_Traits>& queue)
 {
diff --git a/asio/include/asio/detail/impl/epoll_reactor.hpp b/asio/include/asio/detail/impl/epoll_reactor.hpp
index 42d52a7..fe40528 100644
--- a/asio/include/asio/detail/impl/epoll_reactor.hpp
+++ b/asio/include/asio/detail/impl/epoll_reactor.hpp
@@ -17,11 +17,19 @@
 
 #if defined(ASIO_HAS_EPOLL)
 
+#include "asio/detail/scheduler.hpp"
+
 #include "asio/detail/push_options.hpp"
 
 namespace asio {
 namespace detail {
 
+inline void epoll_reactor::post_immediate_completion(
+    reactor_op* op, bool is_continuation)
+{
+  scheduler_.post_immediate_completion(op, is_continuation);
+}
+
 template <typename Time_Traits>
 void epoll_reactor::add_timer_queue(timer_queue<Time_Traits>& queue)
 {
diff --git a/asio/include/asio/detail/impl/kqueue_reactor.hpp b/asio/include/asio/detail/impl/kqueue_reactor.hpp
index 6897dc2..43798c0 100644
--- a/asio/include/asio/detail/impl/kqueue_reactor.hpp
+++ b/asio/include/asio/detail/impl/kqueue_reactor.hpp
@@ -20,11 +20,19 @@
 
 #if defined(ASIO_HAS_KQUEUE)
 
+#include "asio/detail/scheduler.hpp"
+
 #include "asio/detail/push_options.hpp"
 
 namespace asio {
 namespace detail {
 
+inline void kqueue_reactor::post_immediate_completion(
+    reactor_op* op, bool is_continuation)
+{
+  scheduler_.post_immediate_completion(op, is_continuation);
+}
+
 template <typename Time_Traits>
 void kqueue_reactor::add_timer_queue(timer_queue<Time_Traits>& queue)
 {
diff --git a/asio/include/asio/detail/impl/select_reactor.hpp b/asio/include/asio/detail/impl/select_reactor.hpp
index dd4418f..eb855bd 100644
--- a/asio/include/asio/detail/impl/select_reactor.hpp
+++ b/asio/include/asio/detail/impl/select_reactor.hpp
@@ -23,11 +23,19 @@
       && !defined(ASIO_HAS_KQUEUE) \
       && !defined(ASIO_WINDOWS_RUNTIME))
 
+#include "asio/detail/scheduler.hpp"
+
 #include "asio/detail/push_options.hpp"
 
 namespace asio {
 namespace detail {
 
+inline void select_reactor::post_immediate_completion(
+    reactor_op* op, bool is_continuation)
+{
+  scheduler_.post_immediate_completion(op, is_continuation);
+}
+
 template <typename Time_Traits>
 void select_reactor::add_timer_queue(timer_queue<Time_Traits>& queue)
 {
diff --git a/asio/include/asio/detail/kqueue_reactor.hpp b/asio/include/asio/detail/kqueue_reactor.hpp
index 38ae067..664a42b 100644
--- a/asio/include/asio/detail/kqueue_reactor.hpp
+++ b/asio/include/asio/detail/kqueue_reactor.hpp
@@ -24,8 +24,8 @@
 #include <sys/types.h>
 #include <sys/event.h>
 #include <sys/time.h>
+#include "asio/detail/conditionally_enabled_mutex.hpp"
 #include "asio/detail/limits.hpp"
-#include "asio/detail/mutex.hpp"
 #include "asio/detail/object_pool.hpp"
 #include "asio/detail/op_queue.hpp"
 #include "asio/detail/reactor_op.hpp"
@@ -114,10 +114,7 @@
       per_descriptor_data& source_descriptor_data);
 
   // Post a reactor operation for immediate completion.
-  void post_immediate_completion(reactor_op* op, bool is_continuation)
-  {
-    scheduler_.post_immediate_completion(op, is_continuation);
-  }
+  void post_immediate_completion(reactor_op* op, bool is_continuation);
 
   // Start a new operation. The reactor operation will be performed when the
   // given descriptor is flagged as ready, or an error has occurred.
diff --git a/asio/include/asio/detail/select_reactor.hpp b/asio/include/asio/detail/select_reactor.hpp
index 01eb716..96889b0 100644
--- a/asio/include/asio/detail/select_reactor.hpp
+++ b/asio/include/asio/detail/select_reactor.hpp
@@ -90,10 +90,7 @@
       per_descriptor_data& descriptor_data, reactor_op* op);
 
   // Post a reactor operation for immediate completion.
-  void post_immediate_completion(reactor_op* op, bool is_continuation)
-  {
-    scheduler_.post_immediate_completion(op, is_continuation);
-  }
+  void post_immediate_completion(reactor_op* op, bool is_continuation);
 
   // Start a new operation. The reactor operation will be performed when the
   // given descriptor is flagged as ready, or an error has occurred.
diff --git a/asio/include/asio/detail/work_dispatcher.hpp b/asio/include/asio/detail/work_dispatcher.hpp
index bcaf53e..6b53974 100644
--- a/asio/include/asio/detail/work_dispatcher.hpp
+++ b/asio/include/asio/detail/work_dispatcher.hpp
@@ -16,37 +16,37 @@
 #endif // defined(_MSC_VER) && (_MSC_VER >= 1200)
 
 #include "asio/detail/config.hpp"
-#include "asio/associated_executor.hpp"
 #include "asio/associated_allocator.hpp"
 #include "asio/executor_work_guard.hpp"
+#include "asio/is_executor.hpp"
 
 #include "asio/detail/push_options.hpp"
 
 namespace asio {
 namespace detail {
 
-template <typename Handler>
+template <typename Handler, typename Executor>
 class work_dispatcher
 {
 public:
   template <typename CompletionHandler>
-  explicit work_dispatcher(ASIO_MOVE_ARG(CompletionHandler) handler)
-    : work_((get_associated_executor)(handler)),
-      handler_(ASIO_MOVE_CAST(CompletionHandler)(handler))
+  work_dispatcher(ASIO_MOVE_ARG(CompletionHandler) handler,
+      const Executor& handler_ex)
+    : handler_(ASIO_MOVE_CAST(CompletionHandler)(handler)),
+      work_(handler_ex)
   {
   }
 
 #if defined(ASIO_HAS_MOVE)
   work_dispatcher(const work_dispatcher& other)
-    : work_(other.work_),
-      handler_(other.handler_)
+    : handler_(other.handler_),
+      work_(other.work_)
   {
   }
 
   work_dispatcher(work_dispatcher&& other)
-    : work_(ASIO_MOVE_CAST(executor_work_guard<
-        typename associated_executor<Handler>::type>)(other.work_)),
-      handler_(ASIO_MOVE_CAST(Handler)(other.handler_))
+    : handler_(ASIO_MOVE_CAST(Handler)(other.handler_)),
+      work_(ASIO_MOVE_CAST(executor_work_guard<Executor>)(other.work_))
   {
   }
 #endif // defined(ASIO_HAS_MOVE)
@@ -61,8 +61,8 @@
   }
 
 private:
-  executor_work_guard<typename associated_executor<Handler>::type> work_;
   Handler handler_;
+  executor_work_guard<Executor> work_;
 };
 
 } // namespace detail
diff --git a/asio/include/asio/executor_work_guard.hpp b/asio/include/asio/executor_work_guard.hpp
index 6fcb491..e2c903f 100644
--- a/asio/include/asio/executor_work_guard.hpp
+++ b/asio/include/asio/executor_work_guard.hpp
@@ -128,17 +128,6 @@
 }
 
 /// 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,
diff --git a/asio/include/asio/impl/defer.hpp b/asio/include/asio/impl/defer.hpp
index 5346731..1672166 100644
--- a/asio/include/asio/impl/defer.hpp
+++ b/asio/include/asio/impl/defer.hpp
@@ -31,12 +31,11 @@
   template <typename CompletionHandler>
   void operator()(ASIO_MOVE_ARG(CompletionHandler) handler) const
   {
-    typedef typename decay<CompletionHandler>::type DecayedHandler;
+    typedef typename decay<CompletionHandler>::type handler_t;
 
-    typename associated_executor<DecayedHandler>::type ex(
-        (get_associated_executor)(handler));
+    typename handler_t::executor_type ex(handler.get_executor());
 
-    typename associated_allocator<DecayedHandler>::type alloc(
+    typename associated_allocator<handler_t>::type alloc(
         (get_associated_allocator)(handler));
 
     ex.defer(ASIO_MOVE_CAST(CompletionHandler)(handler), alloc);
@@ -50,29 +49,52 @@
   typedef Executor executor_type;
 
   explicit initiate_defer_with_executor(const Executor& ex)
-    : ex_(ex)
+    : io_ex_(ex)
   {
   }
 
   executor_type get_executor() const ASIO_NOEXCEPT
   {
-    return ex_;
+    return io_ex_;
   }
 
   template <typename CompletionHandler>
   void operator()(ASIO_MOVE_ARG(CompletionHandler) handler) const
   {
-    typedef typename decay<CompletionHandler>::type DecayedHandler;
+    typedef typename decay<CompletionHandler>::type handler_t;
 
-    typename associated_allocator<DecayedHandler>::type alloc(
+    typedef typename associated_executor<
+      handler_t, Executor>::type handler_ex_t;
+    handler_ex_t handler_ex((get_associated_executor)(handler, io_ex_));
+
+    typename associated_allocator<handler_t>::type alloc(
         (get_associated_allocator)(handler));
 
-    ex_.defer(detail::work_dispatcher<DecayedHandler>(
-          ASIO_MOVE_CAST(CompletionHandler)(handler)), alloc);
+    if (this->is_same_executor(io_ex_, handler_ex))
+    {
+      io_ex_.defer(ASIO_MOVE_CAST(CompletionHandler)(handler), alloc);
+    }
+    else
+    {
+      io_ex_.defer(detail::work_dispatcher<handler_t, handler_ex_t>(
+            ASIO_MOVE_CAST(CompletionHandler)(handler), handler_ex), alloc);
+    }
   }
 
 private:
-  Executor ex_;
+  template <typename T, typename U>
+  bool is_same_executor(const T&, const U&) const
+  {
+    return false;
+  }
+
+  template <typename T>
+  bool is_same_executor(const T& a, const T& b) const
+  {
+    return a == b;
+  }
+
+  Executor io_ex_;
 };
 
 } // namespace detail
diff --git a/asio/include/asio/impl/dispatch.hpp b/asio/include/asio/impl/dispatch.hpp
index 0b7740b..c19e216 100644
--- a/asio/include/asio/impl/dispatch.hpp
+++ b/asio/include/asio/impl/dispatch.hpp
@@ -31,12 +31,11 @@
   template <typename CompletionHandler>
   void operator()(ASIO_MOVE_ARG(CompletionHandler) handler) const
   {
-    typedef typename decay<CompletionHandler>::type DecayedHandler;
+    typedef typename decay<CompletionHandler>::type handler_t;
 
-    typename associated_executor<DecayedHandler>::type ex(
-        (get_associated_executor)(handler));
+    typename handler_t::executor_type ex(handler.get_executor());
 
-    typename associated_allocator<DecayedHandler>::type alloc(
+    typename associated_allocator<handler_t>::type alloc(
         (get_associated_allocator)(handler));
 
     ex.dispatch(ASIO_MOVE_CAST(CompletionHandler)(handler), alloc);
@@ -50,29 +49,52 @@
   typedef Executor executor_type;
 
   explicit initiate_dispatch_with_executor(const Executor& ex)
-    : ex_(ex)
+    : io_ex_(ex)
   {
   }
 
   executor_type get_executor() const ASIO_NOEXCEPT
   {
-    return ex_;
+    return io_ex_;
   }
 
   template <typename CompletionHandler>
   void operator()(ASIO_MOVE_ARG(CompletionHandler) handler) const
   {
-    typedef typename decay<CompletionHandler>::type DecayedHandler;
+    typedef typename decay<CompletionHandler>::type handler_t;
 
-    typename associated_allocator<DecayedHandler>::type alloc(
+    typedef typename associated_executor<
+      handler_t, Executor>::type handler_ex_t;
+    handler_ex_t handler_ex((get_associated_executor)(handler, io_ex_));
+
+    typename associated_allocator<handler_t>::type alloc(
         (get_associated_allocator)(handler));
 
-    ex_.dispatch(detail::work_dispatcher<DecayedHandler>(
-          ASIO_MOVE_CAST(CompletionHandler)(handler)), alloc);
+    if (this->is_same_executor(io_ex_, handler_ex))
+    {
+      io_ex_.dispatch(ASIO_MOVE_CAST(CompletionHandler)(handler), alloc);
+    }
+    else
+    {
+      io_ex_.dispatch(detail::work_dispatcher<handler_t, handler_ex_t>(
+            ASIO_MOVE_CAST(CompletionHandler)(handler), handler_ex), alloc);
+    }
   }
 
 private:
-  Executor ex_;
+  template <typename T, typename U>
+  bool is_same_executor(const T&, const U&) const
+  {
+    return false;
+  }
+
+  template <typename T>
+  bool is_same_executor(const T& a, const T& b) const
+  {
+    return a == b;
+  }
+
+  Executor io_ex_;
 };
 
 } // namespace detail
diff --git a/asio/include/asio/impl/post.hpp b/asio/include/asio/impl/post.hpp
index 7d01482..9a2dbfc 100644
--- a/asio/include/asio/impl/post.hpp
+++ b/asio/include/asio/impl/post.hpp
@@ -31,12 +31,11 @@
   template <typename CompletionHandler>
   void operator()(ASIO_MOVE_ARG(CompletionHandler) handler) const
   {
-    typedef typename decay<CompletionHandler>::type DecayedHandler;
+    typedef typename decay<CompletionHandler>::type handler_t;
 
-    typename associated_executor<DecayedHandler>::type ex(
-        (get_associated_executor)(handler));
+    typename handler_t::executor_type ex(handler.get_executor());
 
-    typename associated_allocator<DecayedHandler>::type alloc(
+    typename associated_allocator<handler_t>::type alloc(
         (get_associated_allocator)(handler));
 
     ex.post(ASIO_MOVE_CAST(CompletionHandler)(handler), alloc);
@@ -50,29 +49,52 @@
   typedef Executor executor_type;
 
   explicit initiate_post_with_executor(const Executor& ex)
-    : ex_(ex)
+    : io_ex_(ex)
   {
   }
 
   executor_type get_executor() const ASIO_NOEXCEPT
   {
-    return ex_;
+    return io_ex_;
   }
 
   template <typename CompletionHandler>
   void operator()(ASIO_MOVE_ARG(CompletionHandler) handler) const
   {
-    typedef typename decay<CompletionHandler>::type DecayedHandler;
+    typedef typename decay<CompletionHandler>::type handler_t;
 
-    typename associated_allocator<DecayedHandler>::type alloc(
+    typedef typename associated_executor<
+      handler_t, Executor>::type handler_ex_t;
+    handler_ex_t handler_ex((get_associated_executor)(handler, io_ex_));
+
+    typename associated_allocator<handler_t>::type alloc(
         (get_associated_allocator)(handler));
 
-    ex_.post(detail::work_dispatcher<DecayedHandler>(
-          ASIO_MOVE_CAST(CompletionHandler)(handler)), alloc);
+    if (this->is_same_executor(io_ex_, handler_ex))
+    {
+      io_ex_.post(ASIO_MOVE_CAST(CompletionHandler)(handler), alloc);
+    }
+    else
+    {
+      io_ex_.post(detail::work_dispatcher<handler_t, handler_ex_t>(
+            ASIO_MOVE_CAST(CompletionHandler)(handler), handler_ex), alloc);
+    }
   }
 
 private:
-  Executor ex_;
+  template <typename T, typename U>
+  bool is_same_executor(const T&, const U&) const
+  {
+    return false;
+  }
+
+  template <typename T>
+  bool is_same_executor(const T& a, const T& b) const
+  {
+    return a == b;
+  }
+
+  Executor io_ex_;
 };
 
 } // namespace detail
diff --git a/asio/src/examples/cpp14/executors/async_1.cpp b/asio/src/examples/cpp14/executors/async_1.cpp
index d282b74..c63c421 100644
--- a/asio/src/examples/cpp14/executors/async_1.cpp
+++ b/asio/src/examples/cpp14/executors/async_1.cpp
@@ -1,4 +1,5 @@
 #include <asio/ts/executor.hpp>
+#include <asio/system_executor.hpp>
 #include <asio/thread_pool.hpp>
 #include <iostream>
 #include <string>
@@ -7,6 +8,7 @@
 using asio::dispatch;
 using asio::make_work_guard;
 using asio::post;
+using asio::system_executor;
 using asio::thread_pool;
 
 // A function to asynchronously read a single line from an input stream.
@@ -14,10 +16,11 @@
 void async_getline(std::istream& is, Handler handler)
 {
   // Create executor_work for the handler's associated executor.
-  auto work = make_work_guard(handler);
+  auto work = make_work_guard(handler, system_executor());
 
   // Post a function object to do the work asynchronously.
-  post([&is, work, handler=std::move(handler)]() mutable
+  post(system_executor(),
+      [&is, work, handler=std::move(handler)]() mutable
       {
         std::string line;
         std::getline(is, line);
diff --git a/asio/src/examples/cpp14/executors/async_2.cpp b/asio/src/examples/cpp14/executors/async_2.cpp
index b39156d..4e9e99a 100644
--- a/asio/src/examples/cpp14/executors/async_2.cpp
+++ b/asio/src/examples/cpp14/executors/async_2.cpp
@@ -8,6 +8,7 @@
 using asio::get_associated_executor;
 using asio::make_work_guard;
 using asio::post;
+using asio::system_executor;
 using asio::thread_pool;
 
 // A function to asynchronously read a single line from an input stream.
@@ -15,10 +16,11 @@
 void async_getline(std::istream& is, Handler handler)
 {
   // Create executor_work for the handler's associated executor.
-  auto work = make_work_guard(handler);
+  auto work = make_work_guard(handler, system_executor());
 
   // Post a function object to do the work asynchronously.
-  post([&is, work, handler=std::move(handler)]() mutable
+  post(system_executor(),
+      [&is, work, handler=std::move(handler)]() mutable
       {
         std::string line;
         std::getline(is, line);
@@ -37,7 +39,7 @@
 void async_getlines(std::istream& is, std::string init, Handler handler)
 {
   // Get the final handler's associated executor.
-  auto ex = get_associated_executor(handler);
+  auto ex = get_associated_executor(handler, system_executor());
 
   // Use the associated executor for each operation in the composition.
   async_getline(is,
diff --git a/asio/src/tests/unit/archetypes/async_ops.hpp b/asio/src/tests/unit/archetypes/async_ops.hpp
index d3ba7d8..8752482 100644
--- a/asio/src/tests/unit/archetypes/async_ops.hpp
+++ b/asio/src/tests/unit/archetypes/async_ops.hpp
@@ -15,6 +15,7 @@
 #include <asio/associated_executor.hpp>
 #include <asio/async_result.hpp>
 #include <asio/error.hpp>
+#include <asio/system_executor.hpp>
 
 #if defined(ASIO_HAS_BOOST_BIND)
 # include <boost/bind/bind.hpp>
@@ -43,8 +44,8 @@
   typename asio::associated_allocator<handler_type>::type a
     = asio::get_associated_allocator(completion.completion_handler);
 
-  typename asio::associated_executor<handler_type>::type ex
-    = asio::get_associated_executor(completion.completion_handler);
+  typename asio::associated_executor<handler_type, asio::system_executor>::type ex
+    = asio::get_associated_executor(completion.completion_handler, asio::system_executor());
 
   ex.post(ASIO_MOVE_CAST(handler_type)(completion.completion_handler), a);
 
@@ -64,8 +65,8 @@
   typename asio::associated_allocator<handler_type>::type a
     = asio::get_associated_allocator(completion.completion_handler);
 
-  typename asio::associated_executor<handler_type>::type ex
-    = asio::get_associated_executor(completion.completion_handler);
+  typename asio::associated_executor<handler_type, asio::system_executor>::type ex
+    = asio::get_associated_executor(completion.completion_handler, asio::system_executor());
 
   if (ok)
   {
@@ -98,8 +99,8 @@
   typename asio::associated_allocator<handler_type>::type a
     = asio::get_associated_allocator(completion.completion_handler);
 
-  typename asio::associated_executor<handler_type>::type ex
-    = asio::get_associated_executor(completion.completion_handler);
+  typename asio::associated_executor<handler_type, asio::system_executor>::type ex
+    = asio::get_associated_executor(completion.completion_handler, asio::system_executor());
 
   if (ok)
   {
@@ -132,8 +133,8 @@
   typename asio::associated_allocator<handler_type>::type a
     = asio::get_associated_allocator(completion.completion_handler);
 
-  typename asio::associated_executor<handler_type>::type ex
-    = asio::get_associated_executor(completion.completion_handler);
+  typename asio::associated_executor<handler_type, asio::system_executor>::type ex
+    = asio::get_associated_executor(completion.completion_handler, asio::system_executor());
 
   ex.post(
       bindns::bind(
@@ -158,8 +159,8 @@
   typename asio::associated_allocator<handler_type>::type a
     = asio::get_associated_allocator(completion.completion_handler);
 
-  typename asio::associated_executor<handler_type>::type ex
-    = asio::get_associated_executor(completion.completion_handler);
+  typename asio::associated_executor<handler_type, asio::system_executor>::type ex
+    = asio::get_associated_executor(completion.completion_handler, asio::system_executor());
 
   if (ok)
   {
@@ -194,8 +195,8 @@
   typename asio::associated_allocator<handler_type>::type a
     = asio::get_associated_allocator(completion.completion_handler);
 
-  typename asio::associated_executor<handler_type>::type ex
-    = asio::get_associated_executor(completion.completion_handler);
+  typename asio::associated_executor<handler_type, asio::system_executor>::type ex
+    = asio::get_associated_executor(completion.completion_handler, asio::system_executor());
 
   if (ok)
   {
@@ -228,8 +229,8 @@
   typename asio::associated_allocator<handler_type>::type a
     = asio::get_associated_allocator(completion.completion_handler);
 
-  typename asio::associated_executor<handler_type>::type ex
-    = asio::get_associated_executor(completion.completion_handler);
+  typename asio::associated_executor<handler_type, asio::system_executor>::type ex
+    = asio::get_associated_executor(completion.completion_handler, asio::system_executor());
 
   ex.post(
       bindns::bind(
@@ -254,8 +255,8 @@
   typename asio::associated_allocator<handler_type>::type a
     = asio::get_associated_allocator(completion.completion_handler);
 
-  typename asio::associated_executor<handler_type>::type ex
-    = asio::get_associated_executor(completion.completion_handler);
+  typename asio::associated_executor<handler_type, asio::system_executor>::type ex
+    = asio::get_associated_executor(completion.completion_handler, asio::system_executor());
 
   if (ok)
   {
@@ -291,8 +292,8 @@
   typename asio::associated_allocator<handler_type>::type a
     = asio::get_associated_allocator(completion.completion_handler);
 
-  typename asio::associated_executor<handler_type>::type ex
-    = asio::get_associated_executor(completion.completion_handler);
+  typename asio::associated_executor<handler_type, asio::system_executor>::type ex
+    = asio::get_associated_executor(completion.completion_handler, asio::system_executor());
 
   if (ok)
   {
@@ -325,8 +326,8 @@
   typename asio::associated_allocator<handler_type>::type a
     = asio::get_associated_allocator(completion.completion_handler);
 
-  typename asio::associated_executor<handler_type>::type ex
-    = asio::get_associated_executor(completion.completion_handler);
+  typename asio::associated_executor<handler_type, asio::system_executor>::type ex
+    = asio::get_associated_executor(completion.completion_handler, asio::system_executor());
 
   ex.post(
       bindns::bind(
@@ -351,8 +352,8 @@
   typename asio::associated_allocator<handler_type>::type a
     = asio::get_associated_allocator(completion.completion_handler);
 
-  typename asio::associated_executor<handler_type>::type ex
-    = asio::get_associated_executor(completion.completion_handler);
+  typename asio::associated_executor<handler_type, asio::system_executor>::type ex
+    = asio::get_associated_executor(completion.completion_handler, asio::system_executor());
 
   if (ok)
   {
@@ -388,8 +389,8 @@
   typename asio::associated_allocator<handler_type>::type a
     = asio::get_associated_allocator(completion.completion_handler);
 
-  typename asio::associated_executor<handler_type>::type ex
-    = asio::get_associated_executor(completion.completion_handler);
+  typename asio::associated_executor<handler_type, asio::system_executor>::type ex
+    = asio::get_associated_executor(completion.completion_handler, asio::system_executor());
 
   if (ok)
   {