Remove native_scheduler, cache service pointers at proper layers

native_scheduler conflated abstract dispatch, reactor config,
run-loop service access, and construction-time lookup into one
intermediate class. Replace it with proper separation:

- scheduler remains purely abstract (no data members)
- io_context caches timer_svc_ for construction hot-path
- reactor_scheduler owns timer_svc_ and single_threaded_ for
  run-loop access, exposes is_single_threaded() accessor
- win_scheduler owns its own timer_svc_ for run-loop access
- Acceptor services cache tcp_service* at construction, passed
  directly from io_context.cpp, eliminating per-accept
  find_service + dynamic_cast
- Rename reactor_scheduler_base to reactor_scheduler

Author: sgerbino

include/boost/corosio/detail/scheduler.hpp

@@ -26,7 +26,7 @@ class scheduler_op;
     this to implement the reactor/proactor event loop. The
     @ref io_context delegates all scheduling operations here.
 
-    @see io_context, native_scheduler
+    @see io_context
 */
 struct BOOST_COROSIO_DECL scheduler
 {

include/boost/corosio/detail/timer_service.hpp

@@ -14,7 +14,6 @@
 #include <boost/corosio/timer.hpp>
 #include <boost/corosio/io_context.hpp>
 #include <boost/corosio/detail/scheduler_op.hpp>
-#include <boost/corosio/native/native_scheduler.hpp>
 #include <boost/corosio/detail/intrusive.hpp>
 #include <boost/corosio/detail/thread_local_ptr.hpp>
 #include <boost/capy/error.hpp>
@@ -894,18 +893,22 @@ timer_service::implementation::wait(
 
 struct timer_service_access
 {
-    static native_scheduler& get_scheduler(io_context& ctx) noexcept
+    static timer_service& get_timer(io_context& ctx) noexcept
     {
-        return static_cast<native_scheduler&>(*ctx.sched_);
+        return *ctx.timer_svc_;
+    }
+
+    static void set_timer(io_context& ctx, timer_service& svc) noexcept
+    {
+        ctx.timer_svc_ = &svc;
     }
 };
 
-// Bypass find_service() mutex by reading the scheduler's cached pointer
+// Bypass find_service() mutex by reading io_context's cached pointer
 inline io_object::io_service&
 timer_service_direct(capy::execution_context& ctx) noexcept
 {
-    return *timer_service_access::get_scheduler(static_cast<io_context&>(ctx))
-                .timer_svc_;
+    return timer_service_access::get_timer(static_cast<io_context&>(ctx));
 }
 
 inline std::size_t
@@ -932,7 +935,9 @@ timer_service_cancel_one(timer::implementation& base) noexcept
 inline timer_service&
 get_timer_service(capy::execution_context& ctx, scheduler& sched)
 {
-    return ctx.make_service<timer_service>(sched);
+    auto& svc = ctx.make_service<timer_service>(sched);
+    timer_service_access::set_timer(static_cast<io_context&>(ctx), svc);
+    return svc;
 }
 
 } // namespace boost::corosio::detail

include/boost/corosio/io_context.hpp

@@ -117,6 +117,7 @@ struct io_context_options
 };
 
 namespace detail {
+class timer_service;
 struct timer_service_access;
 } // namespace detail
 
@@ -160,6 +161,7 @@ class BOOST_COROSIO_DECL io_context : public capy::execution_context
     void apply_options_post_(io_context_options const& opts);
 
 protected:
+    detail::timer_service* timer_svc_ = nullptr;
     detail::scheduler* sched_;
 
 public:

include/boost/corosio/native/detail/epoll/epoll_scheduler.hpp

@@ -65,7 +65,7 @@ struct descriptor_state;
     @par Thread Safety
     All public member functions are thread-safe.
 */
-class BOOST_COROSIO_DECL epoll_scheduler final : public reactor_scheduler_base
+class BOOST_COROSIO_DECL epoll_scheduler final : public reactor_scheduler
 {
 public:
     /** Construct the scheduler.
@@ -238,7 +238,7 @@ epoll_scheduler::configure_reactor(
     unsigned budget_max,
     unsigned unassisted)
 {
-    reactor_scheduler_base::configure_reactor(
+    reactor_scheduler::configure_reactor(
         max_events, budget_init, budget_max, unassisted);
     event_buffer_.resize(max_events_per_poll_);
 }

include/boost/corosio/native/detail/epoll/epoll_tcp_acceptor_service.hpp

@@ -50,7 +50,8 @@ class BOOST_COROSIO_DECL epoll_tcp_acceptor_service final
     : public tcp_acceptor_service
 {
 public:
-    explicit epoll_tcp_acceptor_service(capy::execution_context& ctx);
+    explicit epoll_tcp_acceptor_service(
+        capy::execution_context& ctx, epoll_tcp_service& tcp_svc);
     ~epoll_tcp_acceptor_service() override;
 
     epoll_tcp_acceptor_service(epoll_tcp_acceptor_service const&) = delete;
@@ -84,7 +85,7 @@ class BOOST_COROSIO_DECL epoll_tcp_acceptor_service final
     epoll_tcp_service* tcp_service() const noexcept;
 
 private:
-    capy::execution_context& ctx_;
+    epoll_tcp_service* tcp_svc_;
     std::unique_ptr<epoll_tcp_acceptor_state> state_;
 };
 
@@ -237,8 +238,8 @@ epoll_tcp_acceptor::close_socket() noexcept
 }
 
 inline epoll_tcp_acceptor_service::epoll_tcp_acceptor_service(
-    capy::execution_context& ctx)
-    : ctx_(ctx)
+    capy::execution_context& ctx, epoll_tcp_service& tcp_svc)
+    : tcp_svc_(&tcp_svc)
     , state_(
           std::make_unique<epoll_tcp_acceptor_state>(
               ctx.use_service<epoll_scheduler>()))
@@ -353,8 +354,7 @@ epoll_tcp_acceptor_service::work_finished() noexcept
 inline epoll_tcp_service*
 epoll_tcp_acceptor_service::tcp_service() const noexcept
 {
-    auto* svc = ctx_.find_service<detail::tcp_service>();
-    return svc ? dynamic_cast<epoll_tcp_service*>(svc) : nullptr;
+    return tcp_svc_;
 }
 
 } // namespace boost::corosio::detail

include/boost/corosio/native/detail/iocp/win_scheduler.hpp

@@ -18,7 +18,7 @@
 #include <boost/corosio/detail/config.hpp>
 #include <boost/capy/ex/execution_context.hpp>
 
-#include <boost/corosio/native/native_scheduler.hpp>
+#include <boost/corosio/detail/scheduler.hpp>
 #include <system_error>
 
 #include <boost/corosio/detail/scheduler_op.hpp>
@@ -48,7 +48,7 @@ struct overlapped_op;
 class win_timers;
 
 class BOOST_COROSIO_DECL win_scheduler final
-    : public native_scheduler
+    : public scheduler
     , public capy::execution_context::service
 {
 public:
@@ -106,6 +106,7 @@ class BOOST_COROSIO_DECL win_scheduler final
     void post_deferred_completions(op_queue& ops);
     std::size_t do_one(unsigned long timeout_ms);
 
+    timer_service* timer_svc_ = nullptr;
     void* iocp_;
     mutable long outstanding_work_;
     mutable long stopped_;

include/boost/corosio/native/detail/kqueue/kqueue_scheduler.hpp

@@ -71,7 +71,7 @@ struct descriptor_state;
     @par Thread Safety
     All public member functions are thread-safe.
 */
-class BOOST_COROSIO_DECL kqueue_scheduler final : public reactor_scheduler_base
+class BOOST_COROSIO_DECL kqueue_scheduler final : public reactor_scheduler
 {
 public:
     /** Construct the scheduler.
@@ -221,7 +221,7 @@ kqueue_scheduler::configure_reactor(
     unsigned budget_max,
     unsigned unassisted)
 {
-    reactor_scheduler_base::configure_reactor(
+    reactor_scheduler::configure_reactor(
         max_events, budget_init, budget_max, unassisted);
     event_buffer_.resize(max_events_per_poll_);
 }

include/boost/corosio/native/detail/kqueue/kqueue_tcp_acceptor_service.hpp

@@ -51,7 +51,8 @@ class BOOST_COROSIO_DECL kqueue_tcp_acceptor_service final
     : public tcp_acceptor_service
 {
 public:
-    explicit kqueue_tcp_acceptor_service(capy::execution_context& ctx);
+    explicit kqueue_tcp_acceptor_service(
+        capy::execution_context& ctx, kqueue_tcp_service& tcp_svc);
     ~kqueue_tcp_acceptor_service();
 
     kqueue_tcp_acceptor_service(kqueue_tcp_acceptor_service const&) = delete;
@@ -84,7 +85,7 @@ class BOOST_COROSIO_DECL kqueue_tcp_acceptor_service final
     kqueue_tcp_service* tcp_service() const noexcept;
 
 private:
-    capy::execution_context& ctx_;
+    kqueue_tcp_service* tcp_svc_;
     std::unique_ptr<kqueue_tcp_acceptor_state> state_;
 };
 
@@ -267,8 +268,8 @@ kqueue_tcp_acceptor::close_socket() noexcept
 }
 
 inline kqueue_tcp_acceptor_service::kqueue_tcp_acceptor_service(
-    capy::execution_context& ctx)
-    : ctx_(ctx)
+    capy::execution_context& ctx, kqueue_tcp_service& tcp_svc)
+    : tcp_svc_(&tcp_svc)
     , state_(
           std::make_unique<kqueue_tcp_acceptor_state>(
               ctx.use_service<kqueue_scheduler>()))
@@ -406,8 +407,7 @@ kqueue_tcp_acceptor_service::work_finished() noexcept
 inline kqueue_tcp_service*
 kqueue_tcp_acceptor_service::tcp_service() const noexcept
 {
-    auto* svc = ctx_.find_service<detail::tcp_service>();
-    return svc ? dynamic_cast<kqueue_tcp_service*>(svc) : nullptr;
+    return tcp_svc_;
 }
 
 } // namespace boost::corosio::detail

include/boost/corosio/native/detail/posix/posix_random_access_file_service.hpp

@@ -15,7 +15,7 @@
 #if BOOST_COROSIO_POSIX
 
 #include <boost/corosio/native/detail/posix/posix_random_access_file.hpp>
-#include <boost/corosio/native/native_scheduler.hpp>
+#include <boost/corosio/native/detail/reactor/reactor_scheduler.hpp>
 #include <boost/corosio/detail/random_access_file_service.hpp>
 #include <boost/corosio/detail/thread_pool.hpp>
 
@@ -81,7 +81,7 @@ class BOOST_COROSIO_DECL posix_random_access_file_service final
         std::filesystem::path const& path,
         file_base::flags mode) override
     {
-        if (static_cast<native_scheduler const*>(sched_)->single_threaded_)
+        if (static_cast<reactor_scheduler const*>(sched_)->is_single_threaded())
             return std::make_error_code(std::errc::operation_not_supported);
         return static_cast<posix_random_access_file&>(impl).open_file(
             path, mode);

include/boost/corosio/native/detail/posix/posix_resolver_service.hpp

@@ -15,7 +15,7 @@
 #if BOOST_COROSIO_POSIX
 
 #include <boost/corosio/native/detail/posix/posix_resolver.hpp>
-#include <boost/corosio/native/native_scheduler.hpp>
+#include <boost/corosio/native/detail/reactor/reactor_scheduler.hpp>
 #include <boost/corosio/detail/thread_pool.hpp>
 
 #include <unordered_map>
@@ -70,8 +70,8 @@ class BOOST_COROSIO_DECL posix_resolver_service final
     /** Return true if single-threaded mode is active. */
     bool single_threaded() const noexcept
     {
-        return static_cast<native_scheduler const*>(sched_)
-            ->single_threaded_;
+        return static_cast<reactor_scheduler const*>(sched_)
+            ->is_single_threaded();
     }
 
 private: