exec::asio::thread_unsafe_completion_token & _use_sender

For general purpose (i.e. potentially multithreaded) use the
asynchronous operations which result when passing the exec::asio::
completion_token and ::use_sender completion tokens must use a recursive
mutex internally. However if the user knows that no multithreaded use
will occur this recursive mutex is pure overhead. Provided the
exec::asio::thread_unsafe_completion_token and _use_sender completion
tokens which do not make use of a recursive mutex for the aforementioned
use case.

Author: RobertLeahy

include/asioexec/completion_token.hpp

@@ -36,9 +36,24 @@ namespace asioexec
                                         "exec::asio::completion_token_t "
                                         "instead.")]] = exec::asio::completion_token_t;
 
+  using thread_unsafe_completion_token_t
+    [[deprecated("asioexec::thread_unsafe_completion_token_t "
+                 "is deprecated. Please use "
+                 "exec::asio::thread_unsafe_completion_token_"
+                 "t instead.")]] = exec::asio::thread_unsafe_completion_token_t;
+
   inline constexpr auto const & completion_token [[deprecated("asioexec::completion_token is "
                                                               "deprecated. Please use "
                                                               "exec::asio::completion_token "
                                                               "instead.")]]
   = exec::asio::completion_token;
+
+  inline constexpr auto const & thread_unsafe_completion_token [[deprecated("asioexec::thread_"
+                                                                            "unsafe_completion_"
+                                                                            "token is deprecated. "
+                                                                            "Please use "
+                                                                            "exec::asio::thread_"
+                                                                            "unsafe_completion_"
+                                                                            "token instead.")]]
+  = exec::asio::thread_unsafe_completion_token;
 }  // namespace asioexec

include/asioexec/use_sender.hpp

@@ -36,8 +36,19 @@ namespace asioexec
                                   "exec::asio::use_sender_t "
                                   "instead.")]] = exec::asio::use_sender_t;
 
+  using thread_unsafe_use_sender_t [[deprecated(
+    "asioexec::thread_unsafe_use_sender_t is deprecated. Please use "
+    "exec::asio::thread_unsafe_use_sender_t instead.")]] = exec::asio::thread_unsafe_use_sender_t;
+
   inline constexpr auto const & use_sender [[deprecated("asioexec::use_sender is deprecated. "
                                                         "Please use exec::asio::use_sender "
                                                         "instead.")]]
   = exec::asio::use_sender;
+
+  inline constexpr auto const & thread_unsafe_use_sender [[deprecated("asioexec::thread_unsafe_use_"
+                                                                      "sender is deprecated. "
+                                                                      "Please use "
+                                                                      "exec::asio::thread_unsafe_"
+                                                                      "use_sender instead.")]]
+  = exec::asio::thread_unsafe_use_sender;
 }  // namespace asioexec

include/exec/asio/completion_token.hpp

@@ -162,10 +162,7 @@ namespace experimental::execution::asio
                                        ::STDEXEC::set_error_t(std::exception_ptr),
                                        ::STDEXEC::set_stopped_t()>;
 
-    template <typename, typename>
-    class completion_handler;
-
-    template <typename Signatures, typename Receiver>
+    template <typename Mutex, typename Signatures, typename Receiver>
     struct operation_state_base
     {
       class frame_;
@@ -180,7 +177,8 @@ namespace experimental::execution::asio
 
       Receiver                       r_;
       asio_impl::cancellation_signal signal_;
-      std::recursive_mutex           m_;
+      STDEXEC_IMMOVABLE_NO_UNIQUE_ADDRESS
+      Mutex                          m_;
       frame_*                        frames_{nullptr};
       std::exception_ptr             ex_;
       bool                           abandoned_{false};
@@ -286,12 +284,13 @@ namespace experimental::execution::asio
         callback_;
     };
 
-    template <typename Signatures, typename Receiver>
+    template <typename Mutex, typename Signatures, typename Receiver>
     class completion_handler
     {
-      operation_state_base<Signatures, Receiver>* self_;
+      using operation_state_type_ = operation_state_base<Mutex, Signatures, Receiver>;
+      operation_state_type_* self_;
      public:
-      explicit completion_handler(operation_state_base<Signatures, Receiver>& self) noexcept
+      explicit completion_handler(operation_state_type_& self) noexcept
         : self_(&self)
       {}
 
@@ -308,7 +307,7 @@ namespace experimental::execution::asio
           //  When this goes out of scope it might send set stopped or set error, or
           //  it might defer that to the executor frames above us on the call stack
           //  (if any)
-          typename operation_state_base<Signatures, Receiver>::frame_ const frame(*self_);
+          typename operation_state_type_::frame_ const frame(*self_);
           self_->abandoned_ = true;
         }
       }
@@ -355,17 +354,21 @@ namespace experimental::execution::asio
         return self_->signal_.slot();
       }
 
-      operation_state_base<Signatures, Receiver>& state() const noexcept
+      operation_state_type_& state() const noexcept
       {
         STDEXEC_ASSERT(self_);
         return *self_;
       }
     };
 
-    template <typename Signatures, typename Receiver, typename Initiation, typename Args>
-    class operation_state : operation_state_base<Signatures, Receiver>
+    template <typename Mutex,
+              typename Signatures,
+              typename Receiver,
+              typename Initiation,
+              typename Args>
+    class operation_state : operation_state_base<Mutex, Signatures, Receiver>
     {
-      using base_ = operation_state_base<Signatures, Receiver>;
+      using base_ = operation_state_base<Mutex, Signatures, Receiver>;
       Initiation init_;
       Args       args_;
      public:
@@ -390,7 +393,7 @@ namespace experimental::execution::asio
             [&](auto&&... args)
             {
               ::STDEXEC::__invoke(static_cast<Initiation&&>(init_),
-                                  completion_handler<Signatures, Receiver>(*this),
+                                  completion_handler<Mutex, Signatures, Receiver>(*this),
                                   static_cast<decltype(args)&&>(args)...);
             },
             std::move(args_));
@@ -415,10 +418,13 @@ namespace experimental::execution::asio
       }
     };
 
-    template <typename Signatures, typename Initiation, typename... Args>
+    template <typename Mutex, typename Signatures, typename Initiation, typename... Args>
     class sender
     {
       using args_type_ = std::tuple<std::decay_t<Args>...>;
+      template <typename Receiver>
+      using operation_state_type_ =
+        operation_state<Mutex, Signatures, std::remove_cvref_t<Receiver>, Initiation, args_type_>;
      public:
       using sender_concept = ::STDEXEC::sender_tag;
 
@@ -445,44 +451,39 @@ namespace experimental::execution::asio
           std::remove_cvref_t<Receiver>,
           ::STDEXEC::completion_signatures_of_t<sender const &, ::STDEXEC::env_of_t<Receiver>>>
       constexpr auto connect(Receiver&& receiver) const & noexcept(
-        std::is_nothrow_constructible_v<
-          operation_state<Signatures, std::remove_cvref_t<Receiver>, Initiation, args_type_>,
-          Receiver,
-          Initiation const &,
-          args_type_ const &>)
+        std::is_nothrow_constructible_v<operation_state_type_<Receiver>,
+                                        Receiver,
+                                        Initiation const &,
+                                        args_type_ const &>)
       {
-        return operation_state<Signatures, std::remove_cvref_t<Receiver>, Initiation, args_type_>(
-          static_cast<Receiver&&>(receiver),
-          init_,
-          args_);
+        return operation_state_type_<Receiver>(static_cast<Receiver&&>(receiver), init_, args_);
       }
 
       template <typename Receiver>
         requires ::STDEXEC::receiver_of<
           std::remove_cvref_t<Receiver>,
           ::STDEXEC::completion_signatures_of_t<sender, ::STDEXEC::env_of_t<Receiver>>>
       constexpr auto connect(Receiver&& receiver) && noexcept(
-        std::is_nothrow_constructible_v<
-          operation_state<Signatures, std::remove_cvref_t<Receiver>, Initiation, args_type_>,
-          Receiver,
-          Initiation,
-          args_type_>)
+        std::is_nothrow_constructible_v<operation_state_type_<Receiver>,
+                                        Receiver,
+                                        Initiation,
+                                        args_type_>)
       {
-        return operation_state<Signatures, std::remove_cvref_t<Receiver>, Initiation, args_type_>(
-          static_cast<Receiver&&>(receiver),
-          static_cast<Initiation&&>(init_),
-          static_cast<args_type_&&>(args_));
+        return operation_state_type_<Receiver>(static_cast<Receiver&&>(receiver),
+                                               static_cast<Initiation&&>(init_),
+                                               static_cast<args_type_&&>(args_));
       }
      private:
       Initiation init_;
       args_type_ args_;
     };
 
-    template <typename Signatures, typename Receiver, typename Executor>
+    template <typename Mutex, typename Signatures, typename Receiver, typename Executor>
     class executor
     {
-      operation_state_base<Signatures, Receiver>& self_;
-      Executor                                    ex_;
+      using operation_state_type_ = operation_state_base<Mutex, Signatures, Receiver>;
+      operation_state_type_& self_;
+      Executor               ex_;
 
       template <typename F>
       constexpr auto wrap_(F f) const noexcept(std::is_nothrow_move_constructible_v<F>)
@@ -493,8 +494,7 @@ namespace experimental::execution::asio
         };
       }
      public:
-      constexpr explicit executor(operation_state_base<Signatures, Receiver>& self,
-                                  Executor const &                            ex) noexcept
+      constexpr explicit executor(operation_state_type_& self, Executor const & ex) noexcept
         : self_(self)
         , ex_(ex)
       {}
@@ -515,7 +515,7 @@ namespace experimental::execution::asio
       constexpr decltype(auto) prefer(Args&&... args) const noexcept
       {
         auto const ex = asio_impl::prefer(ex_, static_cast<Args&&>(args)...);
-        return executor<Signatures, Receiver, std::remove_cvref_t<decltype(ex)>>(self_, ex);
+        return executor<Mutex, Signatures, Receiver, std::remove_cvref_t<decltype(ex)>>(self_, ex);
       }
 
       template <typename... Args>
@@ -525,7 +525,7 @@ namespace experimental::execution::asio
       constexpr decltype(auto) require(Args&&... args) const noexcept
       {
         auto const ex = asio_impl::require(ex_, static_cast<Args&&>(args)...);
-        return executor<Signatures, Receiver, std::remove_cvref_t<decltype(ex)>>(self_, ex);
+        return executor<Mutex, Signatures, Receiver, std::remove_cvref_t<decltype(ex)>>(self_, ex);
       }
 
       template <typename T>
@@ -581,66 +581,86 @@ namespace experimental::execution::asio
       bool operator!=(executor const & rhs) const = default;
     };
 
+    template <typename Mutex>
+    struct token
+    {
+      static constexpr auto as_default_on = asio::as_default_on<token>;
+      template <typename IoObject>
+      using as_default_on_t = asio::as_default_on_t<token, IoObject>;
+    };
+
+    struct null_basic_lockable
+    {
+      constexpr void lock() noexcept {}
+
+      constexpr void unlock() noexcept {}
+    };
+
   }  // namespace detail::completion_token
 
-  struct completion_token_t
-  {
-    static constexpr auto as_default_on = asio::as_default_on<completion_token_t>;
-    template <typename IoObject>
-    using as_default_on_t = asio::as_default_on_t<completion_token_t, IoObject>;
-  };
+  using completion_token_t = detail::completion_token::token<std::recursive_mutex>;
 
   inline completion_token_t const completion_token{};
 
+  using thread_unsafe_completion_token_t =
+    detail::completion_token::token<detail::completion_token::null_basic_lockable>;
+
+  inline thread_unsafe_completion_token_t const thread_unsafe_completion_token{};
+
 }  // namespace experimental::execution::asio
 
 namespace exec = experimental::execution;
 
 namespace ASIOEXEC_ASIO_NAMESPACE
 {
 
-  template <typename... Signatures>
-  struct async_result<::exec::asio::completion_token_t, Signatures...>
+  template <typename Mutex, typename... Signatures>
+  struct async_result<::exec::asio::detail::completion_token::token<Mutex>, Signatures...>
   {
     template <typename Initiation, typename... Args>
       requires(std::is_constructible_v<std::decay_t<Args>, Args> && ...)
-    static constexpr auto
-    initiate(Initiation&& i, ::exec::asio::completion_token_t const &, Args&&... args)
+    static constexpr auto initiate(Initiation&& i,
+                                   ::exec::asio::detail::completion_token::token<Mutex> const &,
+                                   Args&&... args)
     {
       return ::exec::asio::detail::completion_token::sender<
+        Mutex,
         ::exec::asio::detail::completion_token::completion_signatures<Signatures...>,
         std::remove_cvref_t<Initiation>,
         Args...>(static_cast<Initiation&&>(i), static_cast<Args&&>(args)...);
     }
   };
 
-  template <typename Signatures, typename Receiver, typename Executor>
+  template <typename Mutex, typename Signatures, typename Receiver, typename Executor>
   struct associated_executor<
-    ::exec::asio::detail::completion_token::completion_handler<Signatures, Receiver>,
+    ::exec::asio::detail::completion_token::completion_handler<Mutex, Signatures, Receiver>,
     Executor>
   {
-    using type = ::exec::asio::detail::completion_token::executor<Signatures, Receiver, Executor>;
+    using type =
+      ::exec::asio::detail::completion_token::executor<Mutex, Signatures, Receiver, Executor>;
 
-    static type
-    get(::exec::asio::detail::completion_token::completion_handler<Signatures, Receiver> const & h,
-        Executor const & ex) noexcept
+    static type get(::exec::asio::detail::completion_token::completion_handler<Mutex,
+                                                                               Signatures,
+                                                                               Receiver> const & h,
+                    Executor const & ex) noexcept
     {
       return type(h.state(), ex);
     }
   };
 
-  template <typename Signatures, typename Receiver, typename Allocator>
+  template <typename Mutex, typename Signatures, typename Receiver, typename Allocator>
     requires ::STDEXEC::__callable<::STDEXEC::get_allocator_t, ::STDEXEC::env_of_t<Receiver>>
   struct associated_allocator<
-    ::exec::asio::detail::completion_token::completion_handler<Signatures, Receiver>,
+    ::exec::asio::detail::completion_token::completion_handler<Mutex, Signatures, Receiver>,
     Allocator>
   {
     using type = std::remove_cvref_t<decltype(::STDEXEC::get_allocator(
       ::STDEXEC::get_env(std::declval<Receiver const &>())))>;
 
-    static type
-    get(::exec::asio::detail::completion_token::completion_handler<Signatures, Receiver> const & h,
-        ::STDEXEC::__ignore = {}) noexcept
+    static type get(::exec::asio::detail::completion_token::completion_handler<Mutex,
+                                                                               Signatures,
+                                                                               Receiver> const & h,
+                    ::STDEXEC::__ignore = {}) noexcept
     {
       return ::STDEXEC::get_allocator(::STDEXEC::get_env(h.state().r_));
     }