Boost asio，单个 TCP 服务器，多个客户端

2021-12-28 00:00:00 tcp c++ boost boost-asio

我正在创建一个 TCP 服务器，它将使用 boost asio，它将接受来自许多客户端的连接、接收数据并发送确认.问题是我希望能够接受所有客户，但我一次只想与一个客户合作.我希望所有其他事务都保留在队列中.

I am creating a TCP server that will use boost asio which will accept connections from many clients, receive data, and send confirmations. The thing is that I want to be able to accept all the clients but I want to work only with one at a time. I want all the other transactions to be kept in a queue.

示例:

  1. Client1 连接
  2. Client2 连接
  3. Client1 发送数据并请求回复
  4. Client2 发送数据并请求回复
  5. Client2 的请求被放入队列
  6. Client1 的数据被读取，服务器回复，事务结束
  7. Client2 的请求从队列中取出，服务器读取数据，回复事务结束.

所以这介于异步服务器和阻塞服务器之间.我只想一次做一件事，但同时我希望能够将所有客户端套接字及其需求存储在队列中.

So this is something between asynchronous server and blocking server. I want to do just 1 thing at once but at the same time I want to be able to store all client sockets and their demands in the queue.

我能够使用我需要的所有功能创建服务器-客户端通信，但仅限于单线程.一旦客户端断开连接，服务器也会终止.我真的不知道如何开始实施我上面提到的内容.每次连接被接受时我应该打开新线程吗?我应该使用 async_accept 还是阻塞接受?

I was able to create server-client communication with all the functionality that I need but only on single thread. Once client disconnects server is terminated as well. I don't really know how to start implementing what I have mentioned above. Should I open new thread each time connection is accepted? Should I use async_accept or blocking accept?

我已经阅读了 boost::asio 聊天示例，其中许多客户端连接到单个服务器，但这里没有我需要的排队机制.

I have read boost::asio chat example, where many clients connect so single server, but there is no queuing mechanism that I need here.

我知道这篇文章可能有点令人困惑，但 TCP 服务器对我来说是新的，所以我对术语还不够熟悉.也没有要发布的源代码，因为我只是在寻求有关此项目概念的帮助.

I am aware that this post might be a bit confusing but TCP servers are new to me so I am not familiar enough with the terminology. There is also no source code to post because I am asking only for help with concept of this project.

推荐答案

继续接受.

您没有显示代码，但通常看起来像

You show no code, but it typically looks like

void do_accept() {
    acceptor_.async_accept(socket_, [this](boost::system::error_code ec) {
        std::cout << "async_accept -> " << ec.message() << "
";
        if (!ec) {
            std::make_shared<Connection>(std::move(socket_))->start();
            do_accept(); // THIS LINE
        }
    });
}

如果您不包括标记为 //THIS LINE 的行，您确实不会接受超过 1 个连接.

If you don't include the line marked // THIS LINE you will indeed not accept more than 1 connection.

如果这没有帮助，请提供一些我们可以使用的代码.

If this doesn't help, please include some code we can work from.

这仅使用非网络部分的标准库功能.

This uses just standard library features for the non-network part.

网络部分如前所述:

#include <boost/asio.hpp>
#include <boost/asio/high_resolution_timer.hpp>
#include <istream>

using namespace std::chrono_literals;
using Clock = std::chrono::high_resolution_clock;

namespace Shared {
    using PostRequest = std::function<void(std::istream& is)>;
}

namespace Network {

    namespace ba = boost::asio;
    using ba::ip::tcp;
    using error_code = boost::system::error_code;

    using Shared::PostRequest;

    struct Connection : std::enable_shared_from_this<Connection> {
        Connection(tcp::socket&& s, PostRequest poster) : _s(std::move(s)), _poster(poster) {}

        void process() {
            auto self = shared_from_this();
            ba::async_read(_s, _request, [this,self](error_code ec, size_t) {
                if (!ec || ec == ba::error::eof) {
                    std::istream reader(&_request);
                    _poster(reader);
                }
            });
        }

      private:
        tcp::socket   _s;
        ba::streambuf _request;
        PostRequest   _poster;
    };

    struct Server {

        Server(unsigned port, PostRequest poster) : _port(port), _poster(poster) {}

        void run_for(Clock::duration d = 30s) {
            _stop.expires_from_now(d);
            _stop.async_wait([this](error_code ec) { if (!ec) _svc.post([this] { _a.close(); }); });

            _a.listen();

            do_accept();

            _svc.run();
        }
      private:
        void do_accept() {
            _a.async_accept(_s, [this](error_code ec) {
                if (!ec) {
                    std::make_shared<Connection>(std::move(_s), _poster)->process();
                    do_accept();
                }
            });
        }

        unsigned short            _port;
        PostRequest               _poster;

        ba::io_service            _svc;
        ba::high_resolution_timer _stop { _svc };
        tcp::acceptor             _a { _svc, tcp::endpoint {{}, _port } };
        tcp::socket               _s { _svc };
    };
}

到工作服务部分的唯一连接"是在构造时传递给服务器的 PostRequest 处理程序:

The only "connection" to the work service part is the PostRequest handler that is passed to the server at construction:

Network::Server server(6767, handler);

我也选择了异步操作，所以我们可以有一个计时器来停止服务，即使我们不使用任何线程:

I've also opted for async operations, so we can have a timer to stop the service, even though we do not use any threads:

server.run_for(3s); // this blocks

工作部分

这是完全独立的，将使用线程.首先，让我们定义一个Request，和一个线程安全的Queue:

namespace Service {
    struct Request {
        std::vector<char> data; // or whatever you read from the sockets...
    };

    Request parse_request(std::istream& is) {
        Request result;
        result.data.assign(std::istream_iterator<char>(is), {});
        return result;
    }

    struct Queue {
        Queue(size_t max = 50) : _max(max) {}

        void enqueue(Request req) {
            std::unique_lock<std::mutex> lk(mx);
            cv.wait(lk, [this] { return _queue.size() < _max; });
            _queue.push_back(std::move(req));

            cv.notify_one();
        }

        Request dequeue(Clock::time_point deadline) {
            Request req;

            {
                std::unique_lock<std::mutex> lk(mx);
                _peak = std::max(_peak, _queue.size());
                if (cv.wait_until(lk, deadline, [this] { return _queue.size() > 0; })) {
                    req = std::move(_queue.front());
                    _queue.pop_front();
                    cv.notify_one();
                } else {
                    throw std::range_error("dequeue deadline");
                }
            }

            return  req;
        }

        size_t peak_depth() const {
            std::lock_guard<std::mutex> lk(mx);
            return _peak;
        }

      private:
        mutable std::mutex mx;
        mutable std::condition_variable cv;

        size_t _max = 50;
        size_t _peak = 0;
        std::deque<Request> _queue;
    };

这没什么特别的，实际上还没有使用线程.让我们创建一个接受队列引用的工作函数(如果需要，可以启动 1 个以上的工作):

This is nothing special, and doesn't actually use threads yet. Let's make a worker function that accepts a reference to a queue (more than 1 worker can be started if so desired):

    void worker(std::string name, Queue& queue, Clock::duration d = 30s) {
        auto const deadline = Clock::now() + d;

        while(true) try {
            auto r = queue.dequeue(deadline);
            (std::cout << "Worker " << name << " handling request '").write(r.data.data(), r.data.size()) << "'
";
        }
        catch(std::exception const& e) {
            std::cout << "Worker " << name << " got " << e.what() << "
";
            break;
        }
    }
}

main 驱动

这里是 Queue 被实例化并且网络服务器和一些工作线程都启动的地方:

The main Driver

Here's where the Queue gets instantiated and both the network server as well as some worker threads are started:

int main() {
    Service::Queue queue;

    auto handler = [&](std::istream& is) {
            queue.enqueue(Service::parse_request(is));
        };

    Network::Server server(6767, handler);

    std::vector<std::thread> pool;
    pool.emplace_back([&queue] { Service::worker("one", queue, 6s); });
    pool.emplace_back([&queue] { Service::worker("two", queue, 6s); });

    server.run_for(3s); // this blocks

    for (auto& thread : pool)
        if (thread.joinable())
            thread.join();

    std::cout << "Maximum queue depth was " << queue.peak_depth() << "
";
}

现场演示

观看 Coliru 直播

测试负载如下所示:

for a in "hello world" "the quick" "brown fox" "jumped over" "the pangram" "bye world"
do
     netcat 127.0.0.1 6767 <<< "$a" || echo "not sent: '$a'"&
done
wait

它会打印如下内容:

Worker one handling request 'brownfox'
Worker one handling request 'thepangram'
Worker one handling request 'jumpedover'
Worker two handling request 'Worker helloworldone handling request 'byeworld'
Worker one handling request 'thequick'
'
Worker one got dequeue deadline
Worker two got dequeue deadline
Maximum queue depth was 6

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