我是 C++ 新手,但到目前为止,大多数 asio 的东西都有意义。然而,我正在努力让我的 UDPServer 正常工作。
我的问题可能类似于:Trying to write UDP server class, io_context doesn't block
我认为我的 UDPServer 在将工作分配给它的 io_context 之前就停止了。但是,我在调用 io_context.run() 之前向上下文发出工作,所以我不明白为什么。
当然,我并不完全确定我的上述说法是否正确,并且希望得到一些指导。这是我的类(class):
template<typename message_T>
class UDPServer
{
public:
UDPServer(uint16_t port)
: m_socket(m_asioContext, asio::ip::udp::endpoint(asio::ip::udp::v4(), port))
{
m_port = port;
}
virtual ~UDPServer()
{
Stop();
}
public:
// Starts the server!
bool Start()
{
try
{
// Issue a task to the asio context
WaitForMessages();
m_threadContext = std::thread([this]() { m_asioContext.run(); });
}
catch (std::exception& e)
{
// Something prohibited the server from listening
std::cerr << "[SERVER @ PORT " << m_port << "] Exception: " << e.what() << "\n";
return false;
}
std::cout << "[SERVER @ PORT " << m_port << "] Started!\n";
return true;
}
// Stops the server!
void Stop()
{
// Request the context to close
m_asioContext.stop();
// Tidy up the context thread
if (m_threadContext.joinable()) m_threadContext.join();
// Inform someone, anybody, if they care...
std::cout << "[SERVER @ PORT " << m_port << "] Stopped!\n";
}
void WaitForMessages()
{
m_socket.async_receive_from(asio::buffer(vBuffer.data(), vBuffer.size()), m_endpoint,
[this](std::error_code ec, std::size_t length)
{
if (!ec)
{
std::cout << "[SERVER @ PORT " << m_port << "] Got " << length << " bytes \n Data: " << vBuffer.data() << "\n" << "Address: " << m_endpoint.address() << " Port: " << m_endpoint.port() << "\n" << "Data: " << m_endpoint.data() << "\n";
}
else
{
std::cerr << "[SERVER @ PORT " << m_port << "] Exception: " << ec.message() << "\n";
return;
}
WaitForMessages();
}
);
}
void Send(message_T& msg, const asio::ip::udp::endpoint& ep)
{
asio::post(m_asioContext,
[this, msg, ep]()
{
// If the queue has a message in it, then we must
// assume that it is in the process of asynchronously being written.
bool bWritingMessage = !m_messagesOut.empty();
m_messagesOut.push_back(msg);
if (!bWritingMessage)
{
WriteMessage(ep);
}
}
);
}
private:
void WriteMessage(const asio::ip::udp::endpoint& ep)
{
m_socket.async_send_to(asio::buffer(&m_messagesOut.front(), sizeof(message_T)), ep,
[this, ep](std::error_code ec, std::size_t length)
{
if (!ec)
{
m_messagesOut.pop_front();
// If the queue is not empty, there are more messages to send, so
// make this happen by issuing the task to send the next header.
if (!m_messagesOut.empty())
{
WriteMessage(ep);
}
}
else
{
std::cout << "[SERVER @ PORT " << m_port << "] Write Header Fail.\n";
m_socket.close();
}
});
}
void ReadMessage()
{
}
private:
uint16_t m_port = 0;
asio::ip::udp::endpoint m_endpoint;
std::vector<char> vBuffer = std::vector<char>(21);
protected:
TSQueue<message_T> m_messagesIn;
TSQueue<message_T> m_messagesOut;
Message<message_T> m_tempMessageBuf;
asio::io_context m_asioContext;
std::thread m_threadContext;
asio::ip::udp::socket m_socket;
};
}
现在在主函数中调用代码:
enum class TestMsg {
Ping,
Join,
Leave
};
int main() {
Message<TestMsg> msg; // Message is a pretty basic struct that I'm not using yet. When I was, I was only receiving the first 4 bytes - which led me down this path of investigation
msg.id = TestMsg::Join;
msg << "hello";
UDPServer<Message<TestMsg>> server(60000);
}
调用时,服务器在有机会打印“[SERVER] Started”之前立即退出
我将尝试按照链接帖子的描述添加工作防护,但我仍然想了解为什么 io_context 没有足够快地启动工作。
最佳答案
更新(现在我也阅读了问题而不仅仅是代码)
在WaitForMessages
时您可以通过调用 m_socket.async_receive_from
开始收听函数,因为它是异步的,一旦设置监听,该函数就会返回/解除阻塞。因此,只要您实际上没有客户端向您发送某些内容,您的服务器就没有任何作用。仅当它收到某些内容时,才会通过调用 io_context::run
的线程来调用回调。 。所以你需要工作守卫,以便你的线程运行 run
启动后不会立即解锁,但只要工作守卫在,就会阻塞。
通常,如果处理程序中抛出异常并且您仍想继续处理服务器,它还会与 try/while 模式结合使用。
此外,在您发布的代码中,您从未真正调用 UDPServer::Start
!
这是我对答案的第一个想法:
This is normal behavior of ASIO. io_context::run
一旦函数没有工作要做,它就会返回。
因此要更改 run
的行为函数来阻止你必须使用 boost::asio::executor_work_guard<boost::asio::io_context::executor_type>
即所谓的工作 guard 。引用您的 io_context
来构造该对象并保留它,即只要您想让服务器运行就不要让它破坏,即不想让io_context::run
没工作就回来。
既然如此
boost::asio::io_context io_context_;
boost::asio::executor_work_guard<boost::asio::io_context::executor_type> work_guard_;
然后你可以打电话
work_guard_{boost::asio::make_work_guard(io_context_)},
const auto thread_count{std::max<unsigned>(std::thread::hardware_concurrency(), 1)};
std::generate_n(std::back_inserter(this->io_run_threads_),
thread_count,
[this]() {
return std::thread{io_run_loop,
std::ref(this->io_context_), std::ref(this->error_handler_)};
});
void io_run_loop(boost::asio::io_context &context,
const std::function<void(std::exception &)> &error_handler) {
while (true) {
try {
context.run();
break;
} catch (std::exception &e) {
error_handler(e);
}
}
}
然后关闭服务器:
work_guard_.reset();
io_context_.stop();
std::for_each(this->io_run_threads_.begin(), this->io_run_threads_.end(), [](auto &thread) {
if (thread.joinable()) thread.join();
});
为了更正常地关闭,您可以省略 stop
调用并关闭所有套接字之前。
关于在线程中运行的 C++ UDP 服务器 io_context 在工作开始之前退出,我们在Stack Overflow上找到一个类似的问题: https://stackoverflow.com/questions/69457434/