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+//
+// detail/strand_service.hpp
+// ~~~~~~~~~~~~~~~~~~~~~~~~~
+//
+// Copyright (c) 2003-2018 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_SERVICE_HPP
+#define ASIO_DETAIL_STRAND_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/io_context.hpp"
+#include "asio/detail/mutex.hpp"
+#include "asio/detail/op_queue.hpp"
+#include "asio/detail/operation.hpp"
+#include "asio/detail/scoped_ptr.hpp"
+
+#include "asio/detail/push_options.hpp"
+
+namespace asio {
+namespace detail {
+
+// Default service implementation for a strand.
+class strand_service
+ : public asio::detail::service_base<strand_service>
+{
+private:
+ // Helper class to re-post the strand on exit.
+ struct on_do_complete_exit;
+
+ // Helper class to re-post the strand on exit.
+ struct on_dispatch_exit;
+
+public:
+
+ // The underlying implementation of a strand.
+ class strand_impl
+ : public operation
+ {
+ public:
+ strand_impl();
+
+ private:
+ // Only this service will have access to the internal values.
+ friend class strand_service;
+ friend struct on_do_complete_exit;
+ friend struct on_dispatch_exit;
+
+ // Mutex to protect access to internal data.
+ asio::detail::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_;
+
+ // 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<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<operation> ready_queue_;
+ };
+
+ typedef strand_impl* implementation_type;
+
+ // Construct a new strand service for the specified io_context.
+ ASIO_DECL explicit strand_service(asio::io_context& io_context);
+
+ // Destroy all user-defined handler objects owned by the service.
+ ASIO_DECL void shutdown();
+
+ // Construct a new strand implementation.
+ ASIO_DECL void construct(implementation_type& impl);
+
+ // Request the io_context to invoke the given handler.
+ template <typename Handler>
+ void dispatch(implementation_type& impl, Handler& handler);
+
+ // Request the io_context to invoke the given handler and return immediately.
+ template <typename Handler>
+ void post(implementation_type& impl, Handler& handler);
+
+ // Determine whether the strand is running in the current thread.
+ ASIO_DECL bool running_in_this_thread(
+ const implementation_type& impl) const;
+
+private:
+ // Helper function to dispatch a handler. Returns true if the handler should
+ // be dispatched immediately.
+ ASIO_DECL bool do_dispatch(implementation_type& impl, operation* op);
+
+ // Helper fiunction to post a handler.
+ ASIO_DECL void do_post(implementation_type& impl,
+ operation* op, bool is_continuation);
+
+ ASIO_DECL static void do_complete(void* owner,
+ operation* base, const asio::error_code& ec,
+ std::size_t bytes_transferred);
+
+ // The io_context implementation used to post completions.
+ io_context_impl& io_context_;
+
+ // Mutex to protect access to the array of implementations.
+ asio::detail::mutex mutex_;
+
+ // Number of implementations shared between all strand objects.
+#if defined(ASIO_STRAND_IMPLEMENTATIONS)
+ enum { num_implementations = ASIO_STRAND_IMPLEMENTATIONS };
+#else // defined(ASIO_STRAND_IMPLEMENTATIONS)
+ enum { num_implementations = 193 };
+#endif // defined(ASIO_STRAND_IMPLEMENTATIONS)
+
+ // Pool of implementations.
+ scoped_ptr<strand_impl> implementations_[num_implementations];
+
+ // Extra value used when hashing to prevent recycled memory locations from
+ // getting the same strand implementation.
+ std::size_t salt_;
+};
+
+} // namespace detail
+} // namespace asio
+
+#include "asio/detail/pop_options.hpp"
+
+#include "asio/detail/impl/strand_service.hpp"
+#if defined(ASIO_HEADER_ONLY)
+# include "asio/detail/impl/strand_service.ipp"
+#endif // defined(ASIO_HEADER_ONLY)
+
+#endif // ASIO_DETAIL_STRAND_SERVICE_HPP