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+//
+// logger_service.hpp
+// ~~~~~~~~~~~~~~~~~~
+//
+// Copyright (c) 2003-2021 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 SERVICES_LOGGER_SERVICE_HPP
+#define SERVICES_LOGGER_SERVICE_HPP
+
+#include <asio.hpp>
+#include <boost/bind/bind.hpp>
+#include <boost/date_time/posix_time/posix_time.hpp>
+#include <boost/noncopyable.hpp>
+#include <boost/scoped_ptr.hpp>
+#include <fstream>
+#include <sstream>
+#include <string>
+
+namespace services {
+
+/// Service implementation for the logger.
+class logger_service
+ : public asio::execution_context::service
+{
+public:
+ /// The type used to identify this service in the execution context.
+ typedef logger_service key_type;
+
+ /// The backend implementation of a logger.
+ struct logger_impl
+ {
+ explicit logger_impl(const std::string& ident) : identifier(ident) {}
+ std::string identifier;
+ };
+
+ /// The type for an implementation of the logger.
+ typedef logger_impl* impl_type;
+
+ /// Constructor creates a thread to run a private io_context.
+ logger_service(asio::execution_context& context)
+ : asio::execution_context::service(context),
+ work_io_context_(),
+ work_(asio::require(work_io_context_.get_executor(),
+ asio::execution::outstanding_work.tracked)),
+ work_thread_(new asio::thread(
+ boost::bind(&asio::io_context::run, &work_io_context_)))
+ {
+ }
+
+ /// Destructor shuts down the private io_context.
+ ~logger_service()
+ {
+ /// Indicate that we have finished with the private io_context. Its
+ /// io_context::run() function will exit once all other work has completed.
+ work_ = asio::any_io_executor();
+ if (work_thread_)
+ work_thread_->join();
+ }
+
+ /// Destroy all user-defined handler objects owned by the service.
+ void shutdown()
+ {
+ }
+
+ /// Return a null logger implementation.
+ impl_type null() const
+ {
+ return 0;
+ }
+
+ /// Create a new logger implementation.
+ void create(impl_type& impl, const std::string& identifier)
+ {
+ impl = new logger_impl(identifier);
+ }
+
+ /// Destroy a logger implementation.
+ void destroy(impl_type& impl)
+ {
+ delete impl;
+ impl = null();
+ }
+
+ /// Set the output file for the logger. The current implementation sets the
+ /// output file for all logger instances, and so the impl parameter is not
+ /// actually needed. It is retained here to illustrate how service functions
+ /// are typically defined.
+ void use_file(impl_type& /*impl*/, const std::string& file)
+ {
+ // Pass the work of opening the file to the background thread.
+ asio::post(work_io_context_, boost::bind(
+ &logger_service::use_file_impl, this, file));
+ }
+
+ /// Log a message.
+ void log(impl_type& impl, const std::string& message)
+ {
+ // Format the text to be logged.
+ std::ostringstream os;
+ os << impl->identifier << ": " << message;
+
+ // Pass the work of writing to the file to the background thread.
+ asio::post(work_io_context_, boost::bind(
+ &logger_service::log_impl, this, os.str()));
+ }
+
+private:
+ /// Helper function used to open the output file from within the private
+ /// io_context's thread.
+ void use_file_impl(const std::string& file)
+ {
+ ofstream_.close();
+ ofstream_.clear();
+ ofstream_.open(file.c_str());
+ }
+
+ /// Helper function used to log a message from within the private io_context's
+ /// thread.
+ void log_impl(const std::string& text)
+ {
+ ofstream_ << text << std::endl;
+ }
+
+ /// Private io_context used for performing logging operations.
+ asio::io_context work_io_context_;
+
+ /// A work-tracking executor giving work for the private io_context to
+ /// perform. If we do not give the io_context some work to do then the
+ /// io_context::run() function will exit immediately.
+ asio::any_io_executor work_;
+
+ /// Thread used for running the work io_context's run loop.
+ boost::scoped_ptr<asio::thread> work_thread_;
+
+ /// The file to which log messages will be written.
+ std::ofstream ofstream_;
+};
+
+} // namespace services
+
+#endif // SERVICES_LOGGER_SERVICE_HPP