| // |
| // process_per_connection.cpp |
| // ~~~~~~~~~~~~~~~~~~~~~~~~~~ |
| // |
| // 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) |
| // |
| |
| #include <boost/asio/io_context.hpp> |
| #include <boost/asio/ip/tcp.hpp> |
| #include <boost/asio/signal_set.hpp> |
| #include <boost/asio/write.hpp> |
| #include <cstdlib> |
| #include <iostream> |
| #include <sys/types.h> |
| #include <sys/wait.h> |
| #include <unistd.h> |
| |
| using boost::asio::ip::tcp; |
| |
| class server |
| { |
| public: |
| server(boost::asio::io_context& io_context, unsigned short port) |
| : io_context_(io_context), |
| signal_(io_context, SIGCHLD), |
| acceptor_(io_context, {tcp::v4(), port}), |
| socket_(io_context) |
| { |
| wait_for_signal(); |
| accept(); |
| } |
| |
| private: |
| void wait_for_signal() |
| { |
| signal_.async_wait( |
| [this](boost::system::error_code /*ec*/, int /*signo*/) |
| { |
| // Only the parent process should check for this signal. We can |
| // determine whether we are in the parent by checking if the acceptor |
| // is still open. |
| if (acceptor_.is_open()) |
| { |
| // Reap completed child processes so that we don't end up with |
| // zombies. |
| int status = 0; |
| while (waitpid(-1, &status, WNOHANG) > 0) {} |
| |
| wait_for_signal(); |
| } |
| }); |
| } |
| |
| void accept() |
| { |
| acceptor_.async_accept( |
| [this](boost::system::error_code ec, tcp::socket new_socket) |
| { |
| if (!ec) |
| { |
| // Take ownership of the newly accepted socket. |
| socket_ = std::move(new_socket); |
| |
| // Inform the io_context that we are about to fork. The io_context |
| // cleans up any internal resources, such as threads, that may |
| // interfere with forking. |
| io_context_.notify_fork(boost::asio::io_context::fork_prepare); |
| |
| if (fork() == 0) |
| { |
| // Inform the io_context that the fork is finished and that this |
| // is the child process. The io_context uses this opportunity to |
| // create any internal file descriptors that must be private to |
| // the new process. |
| io_context_.notify_fork(boost::asio::io_context::fork_child); |
| |
| // The child won't be accepting new connections, so we can close |
| // the acceptor. It remains open in the parent. |
| acceptor_.close(); |
| |
| // The child process is not interested in processing the SIGCHLD |
| // signal. |
| signal_.cancel(); |
| |
| read(); |
| } |
| else |
| { |
| |
| // Inform the io_context that the fork is finished (or failed) |
| // and that this is the parent process. The io_context uses this |
| // opportunity to recreate any internal resources that were |
| // cleaned up during preparation for the fork. |
| io_context_.notify_fork(boost::asio::io_context::fork_parent); |
| |
| // The parent process can now close the newly accepted socket. It |
| // remains open in the child. |
| socket_.close(); |
| |
| accept(); |
| } |
| } |
| else |
| { |
| std::cerr << "Accept error: " << ec.message() << std::endl; |
| accept(); |
| } |
| }); |
| } |
| |
| void read() |
| { |
| socket_.async_read_some(boost::asio::buffer(data_), |
| [this](boost::system::error_code ec, std::size_t length) |
| { |
| if (!ec) |
| write(length); |
| }); |
| } |
| |
| void write(std::size_t length) |
| { |
| boost::asio::async_write(socket_, boost::asio::buffer(data_, length), |
| [this](boost::system::error_code ec, std::size_t /*length*/) |
| { |
| if (!ec) |
| read(); |
| }); |
| } |
| |
| boost::asio::io_context& io_context_; |
| boost::asio::signal_set signal_; |
| tcp::acceptor acceptor_; |
| tcp::socket socket_; |
| std::array<char, 1024> data_; |
| }; |
| |
| int main(int argc, char* argv[]) |
| { |
| try |
| { |
| if (argc != 2) |
| { |
| std::cerr << "Usage: process_per_connection <port>\n"; |
| return 1; |
| } |
| |
| boost::asio::io_context io_context; |
| |
| using namespace std; // For atoi. |
| server s(io_context, atoi(argv[1])); |
| |
| io_context.run(); |
| } |
| catch (std::exception& e) |
| { |
| std::cerr << "Exception: " << e.what() << std::endl; |
| } |
| } |