Initial Commit

include/asio/detail/strand_executor_service.hpp

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+//
+// detail/strand_executor_service.hpp
+// ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+//
+// Copyright (c) 2003-2025 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_DETAIL_STRAND_EXECUTOR_SERVICE_HPP
+#define ASIO_DETAIL_STRAND_EXECUTOR_SERVICE_HPP
+
+#if defined(_MSC_VER) && (_MSC_VER >= 1200)
+# pragma once
+#endif // defined(_MSC_VER) && (_MSC_VER >= 1200)
+
+#include "asio/detail/config.hpp"
+#include "asio/detail/atomic_count.hpp"
+#include "asio/detail/executor_op.hpp"
+#include "asio/detail/memory.hpp"
+#include "asio/detail/mutex.hpp"
+#include "asio/detail/op_queue.hpp"
+#include "asio/detail/scheduler_operation.hpp"
+#include "asio/detail/type_traits.hpp"
+#include "asio/execution.hpp"
+#include "asio/execution_context.hpp"
+
+#include "asio/detail/push_options.hpp"
+
+namespace asio {
+namespace detail {
+
+// Default service implementation for a strand.
+class strand_executor_service
+  : public execution_context_service_base<strand_executor_service>
+{
+public:
+  // The underlying implementation of a strand.
+  class strand_impl
+  {
+  public:
+    ASIO_DECL ~strand_impl();
+
+  private:
+    friend class strand_executor_service;
+
+    // Mutex to protect access to internal data.
+    mutex* mutex_;
+
+    // Indicates whether the strand is currently "locked" by a handler. This
+    // means that there is a handler upcall in progress, or that the strand
+    // itself has been scheduled in order to invoke some pending handlers.
+    bool locked_;
+
+    // Indicates that the strand has been shut down and will accept no further
+    // handlers.
+    bool shutdown_;
+
+    // The handlers that are waiting on the strand but should not be run until
+    // after the next time the strand is scheduled. This queue must only be
+    // modified while the mutex is locked.
+    op_queue<scheduler_operation> waiting_queue_;
+
+    // The handlers that are ready to be run. Logically speaking, these are the
+    // handlers that hold the strand's lock. The ready queue is only modified
+    // from within the strand and so may be accessed without locking the mutex.
+    op_queue<scheduler_operation> ready_queue_;
+
+    // Pointers to adjacent handle implementations in linked list.
+    strand_impl* next_;
+    strand_impl* prev_;
+
+    // The strand service in where the implementation is held.
+    strand_executor_service* service_;
+  };
+
+  typedef shared_ptr<strand_impl> implementation_type;
+
+  // Construct a new strand service for the specified context.
+  ASIO_DECL explicit strand_executor_service(execution_context& context);
+
+  // Destroy all user-defined handler objects owned by the service.
+  ASIO_DECL void shutdown();
+
+  // Create a new strand_executor implementation.
+  ASIO_DECL implementation_type create_implementation();
+
+  // Request invocation of the given function.
+  template <typename Executor, typename Function>
+  static void execute(const implementation_type& impl, Executor& ex,
+      Function&& function,
+      enable_if_t<
+        can_query<Executor, execution::allocator_t<void>>::value
+      >* = 0);
+
+  // Request invocation of the given function.
+  template <typename Executor, typename Function>
+  static void execute(const implementation_type& impl, Executor& ex,
+      Function&& function,
+      enable_if_t<
+        !can_query<Executor, execution::allocator_t<void>>::value
+      >* = 0);
+
+  // Request invocation of the given function.
+  template <typename Executor, typename Function, typename Allocator>
+  static void dispatch(const implementation_type& impl, Executor& ex,
+      Function&& function, const Allocator& a);
+
+  // Request invocation of the given function and return immediately.
+  template <typename Executor, typename Function, typename Allocator>
+  static void post(const implementation_type& impl, Executor& ex,
+      Function&& function, const Allocator& a);
+
+  // Request invocation of the given function and return immediately.
+  template <typename Executor, typename Function, typename Allocator>
+  static void defer(const implementation_type& impl, Executor& ex,
+      Function&& function, const Allocator& a);
+
+  // Determine whether the strand is running in the current thread.
+  ASIO_DECL static bool running_in_this_thread(
+      const implementation_type& impl);
+
+private:
+  friend class strand_impl;
+  template <typename F, typename Allocator> class allocator_binder;
+  template <typename Executor, typename = void> class invoker;
+
+  // Adds a function to the strand. Returns true if it acquires the lock.
+  ASIO_DECL static bool enqueue(const implementation_type& impl,
+      scheduler_operation* op);
+
+  // Transfers waiting handlers to the ready queue. Returns true if one or more
+  // handlers were transferred.
+  ASIO_DECL static bool push_waiting_to_ready(implementation_type& impl);
+
+  // Invokes all ready-to-run handlers.
+  ASIO_DECL static void run_ready_handlers(implementation_type& impl);
+
+  // Helper function to request invocation of the given function.
+  template <typename Executor, typename Function, typename Allocator>
+  static void do_execute(const implementation_type& impl, Executor& ex,
+      Function&& function, const Allocator& a);
+
+  // Mutex to protect access to the service-wide state.
+  mutex mutex_;
+
+  // Number of mutexes shared between all strand objects.
+  enum { num_mutexes = 193 };
+
+  // Pool of mutexes.
+  shared_ptr<mutex> mutexes_[num_mutexes];
+
+  // Extra value used when hashing to prevent recycled memory locations from
+  // getting the same mutex.
+  std::size_t salt_;
+
+  // The head of a linked list of all implementations.
+  strand_impl* impl_list_;
+};
+
+} // namespace detail
+} // namespace asio
+
+#include "asio/detail/pop_options.hpp"
+
+#include "asio/detail/impl/strand_executor_service.hpp"
+#if defined(ASIO_HEADER_ONLY)
+# include "asio/detail/impl/strand_executor_service.ipp"
+#endif // defined(ASIO_HEADER_ONLY)
+
+#endif // ASIO_DETAIL_STRAND_EXECUTOR_SERVICE_HPP