我试图将一些在Linux中作为控制台应用程序运行的演示代码与守护进程争论。
SDK是用c ++编写的，所以我去寻找能够完成守护进程需要做的所有事情的c ++代码，即启动，分叉，分离，将std com重定向到syslog，处理信号等。
所以我找到了这个例子：
// daemon.cpp
// ~~~~~~~~~~
//
// Copyright (c) 2003-2011 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_service.hpp>
#include <boost/asio/ip/udp.hpp>
#include <boost/asio/signal_set.hpp>
#include <boost/array.hpp>
#include <boost/bind.hpp>
#include <ctime>
#include <iostream>
#include <syslog.h>
#include <unistd.h>
using boost::asio::ip::udp;
class udp_daytime_server
{
public:
udp_daytime_server(boost::asio::io_service& io_service)
: socket_(io_service, udp::endpoint(udp::v4(), 13))
{
start_receive();
}
private:
void start_receive()
{
socket_.async_receive_from(
boost::asio::buffer(recv_buffer_), remote_endpoint_,
boost::bind(&udp_daytime_server::handle_receive, this, _1));
}
void handle_receive(const boost::system::error_code& ec)
{
if (!ec || ec == boost::asio::error::message_size)
{
using namespace std; // For time_t, time and ctime;
time_t now = time(0);
std::string message = ctime(&now);
boost::system::error_code ignored_ec;
socket_.send_to(boost::asio::buffer(message),
remote_endpoint_, 0, ignored_ec);
}
start_receive();
}
udp::socket socket_;
udp::endpoint remote_endpoint_;
boost::array<char, 1> recv_buffer_;
};
int main()
{
try
{
boost::asio::io_service io_service;
// Initialise the server before becoming a daemon. If the process is
// started from a shell, this means any errors will be reported back to the
// user.
udp_daytime_server server(io_service);
// Register signal handlers so that the daemon may be shut down. You may
// also want to register for other signals, such as SIGHUP to trigger a
// re-read of a configuration file.
boost::asio::signal_set signals(io_service, SIGINT, SIGTERM);
signals.async_wait(
boost::bind(&boost::asio::io_service::stop, &io_service));
// Inform the io_service that we are about to become a daemon. The
// io_service cleans up any internal resources, such as threads, that may
// interfere with forking.
io_service.notify_fork(boost::asio::io_service::fork_prepare);
// Fork the process and have the parent exit. If the process was started
// from a shell, this returns control to the user. Forking a new process is
// also a prerequisite for the subsequent call to setsid().
if (pid_t pid = fork())
{
if (pid > 0)
{
// We're in the parent process and need to exit.
//
// When the exit() function is used, the program terminates without
// invoking local variables' destructors. Only global variables are
// destroyed. As the io_service object is a local variable, this means
// we do not have to call:
//
// io_service.notify_fork(boost::asio::io_service::fork_parent);
//
// However, this line should be added before each call to exit() if
// using a global io_service object. An additional call:
//
// io_service.notify_fork(boost::asio::io_service::fork_prepare);
//
// should also precede the second fork().
exit(0);
}
else
{
syslog(LOG_ERR | LOG_USER, "First fork failed: %m");
return 1;
}
}
// Make the process a new session leader. This detaches it from the
// terminal.
setsid();
// A process inherits its working directory from its parent. This could be
// on a mounted filesystem, which means that the running daemon would
// prevent this filesystem from being unmounted. Changing to the root
// directory avoids this problem.
chdir("/");
// The file mode creation mask is also inherited from the parent process.
// We don't want to restrict the permissions on files created by the
// daemon, so the mask is cleared.
umask(0);
// A second fork ensures the process cannot acquire a controlling terminal.
if (pid_t pid = fork())
{
if (pid > 0)
{
exit(0);
}
else
{
syslog(LOG_ERR | LOG_USER, "Second fork failed: %m");
return 1;
}
}
// Close the standard streams. This decouples the daemon from the terminal
// that started it.
close(0);
close(1);
close(2);
// We don't want the daemon to have any standard input.
if (open("/dev/null", O_RDONLY) < 0)
{
syslog(LOG_ERR | LOG_USER, "Unable to open /dev/null: %m");
return 1;
}
// Send standard output to a log file.
const char* output = "/tmp/asio.daemon.out";
const int flags = O_WRONLY | O_CREAT | O_APPEND;
const mode_t mode = S_IRUSR | S_IWUSR | S_IRGRP | S_IROTH;
if (open(output, flags, mode) < 0)
{
syslog(LOG_ERR | LOG_USER, "Unable to open output file %s: %m", output);
return 1;
}
// Also send standard error to the same log file.
if (dup(1) < 0)
{
syslog(LOG_ERR | LOG_USER, "Unable to dup output descriptor: %m");
return 1;
}
// Inform the io_service that we have finished becoming a daemon. The
// io_service uses this opportunity to create any internal file descriptors
// that need to be private to the new process.
io_service.notify_fork(boost::asio::io_service::fork_child);
// The io_service can now be used normally.
syslog(LOG_INFO | LOG_USER, "Daemon started");
io_service.run();
syslog(LOG_INFO | LOG_USER, "Daemon stopped");
}
catch (std::exception& e)
{
syslog(LOG_ERR | LOG_USER, "Exception: %s", e.what());
std::cerr << "Exception: " << e.what() << std::endl;
}
}
无论如何，我想知道，这是一个很好的选择，让最小的守护进程启动并运行（替换udp服务器代码并替换我自己的代码），或者我应该研究另一种获取守护进程功能的方法。
我也很困惑我应该从哪里开始我的代码，因为这个例子的最后一步是调用io_service.run（）。
我的代码将有两个线程，一个用于侦听连接，另一个用于每隔10秒处理挂起的连接 - >来自连接客户端的更新没有时间关键的更新窗口，甚至偶尔可以跳过。
谢谢。
答案 0 :(得分：2)
如果您正在寻找快速简便的实施方案，那么这可能是一个好主意。至少，它提供了一种处理信号的更高级别的方法，否则可能需要对较低级别的机制进行相当详细的理解才能得到正确的信息。快速实现可能如下所示：
void connection_thread_main( bool& running )
{
while ( running )
...
}
int main()
{
...
syslog(LOG_INFO | LOG_USER, "Daemon started");
// Create flag to indicate if daemon is running. This is used as the
// condition for which the thread's while loop continue.
bool running = true;
// Create threads.
boost::thread_group threads;
threads.create_thread( boost::bind( &connection_thread_main,
boost::ref( running ) ) );
threads.create_thread( boost::bind( &pending_thread_main,
boost::ref( running ) ) );
// This will block the main thread as long as there is work queued into the
// service. In this case, signals are being waited on asynchronously.
io_service.run();
// On SIGINT or SIGTERM, io_service.stop() is invoked, causing the main
// thread to return from io_service.run().
// Set the running flag to false and wait on the other threads to finish.
running = false;
threads.join_all();
syslog(LOG_INFO | LOG_USER, "Daemon stopped");
}
有几点需要考虑：
在快速实施中，我选择使解决方案尽可能可读。因此，主线程基本上被浪费了，因为它只是在等待信号。可以将其中一个线程的内容放入main中的循环中，而不是定期poll io_service。
syslog(LOG_INFO | LOG_USER, "Daemon started");
// Create flag to indicate if daemon is running. This is used as the
// condition for which the thread's while loop continue.
bool running = true;
// Create threads.
boost::thread_group threads;
threads.create_thread( boost::bind( &connection_thread_main,
boost::ref( running ) ) );
for ( ;; )
{
// Execute ready to run handlers, but do not block waiting for
// outstanding handlers to become ready. When SIGINT or SIGTERM are
// received, the handler will be ready to run, and ran from the poll
// call, causing the io_service to stop.
io_service.poll();
if ( io_service.stopped() ) break;
... // pending_thread_main's while body content
}
// Set the running flag to false and wait on the other threads to finish.
running = false;
threads.join_all();
syslog(LOG_INFO | LOG_USER, "Daemon stopped");