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//
// logger_service.hpp
// ~~~~~~~~~~~~~~~~~~
//
// Copyright (c) 2003-2020 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 <boost/asio.hpp>
#include <boost/thread/thread.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 boost::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(boost::asio::execution_context& context)
: boost::asio::execution_context::service(context),
work_io_context_(),
work_(boost::asio::require(work_io_context_.get_executor(),
boost::asio::execution::outstanding_work.tracked)),
work_thread_(new boost::thread(
boost::bind(&boost::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_ = boost::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.
boost::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.
boost::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.
boost::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.
boost::asio::any_io_executor work_;
/// Thread used for running the work io_context's run loop.
boost::scoped_ptr<boost::thread> work_thread_;
/// The file to which log messages will be written.
std::ofstream ofstream_;
};
} // namespace services
#endif // SERVICES_LOGGER_SERVICE_HPP
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