Question

我正在尝试使用执行以下操作的asio编写客户端：

连接服务器。
尝试在连接到服务器之后读回一些数据。

我发现的问题是操作似乎没有像我期望的那样按顺序执行。这是代码：

std::future<NetMessage> Cliente::asyncConnectTo(std::string const & hostname, int port, std::string const & name) { using namespace std::literals; boost::asio::spawn (strand_, [this, name, port, hostname](boost::asio::yield_context yield) mutable { i_->playerLog->trace() << name << " connecting to " << hostname << ':' << port; Guinyote::Utils::connectWith (*this, std::move(hostname), port, std::move(name), yield); i_->playerLog->info() << "Connected to server."; }); runthread_ = std::thread([&] { try { i_->playerLog->info() << "Starting..."; this->service_.run(); } catch (std::exception & e) { std::cout << e.what() << std::endl; } }); return this->asyncReceiveMessage(); //This function spawns another coroutine through the same strand_ object. }

函数this->asyncReceiveMessage()应该会在连接后收到服务器发回的消息：

std::future<NetMessage> Cliente::asyncReceiveMessage() { namespace ba = boost::asio; std::promise<NetMessage> prom; std::future<NetMessage> message = prom.get_future(); ba::spawn (strand_, [this, p = std::move(prom)](boost::asio::yield_context yield) mutable { i_->playerLog->trace("waiting to read message from server socket..."); boost::system::error_code ec{}; boost::int64_t messageSize{}; ba::async_read( socket_, ba::buffer(&messageSize, sizeof(boost::int64_t)), yield); i_->playerLog->trace() << "Client: Received message of " << messageSize << " bytes. Reading message..."; std::vector<char> serverMessageData(messageSize); ba::async_read (socket_, ba::buffer(serverMessageData), yield); using namespace boost::iostreams; basic_array_source<char> input_source(&serverMessageData[0], serverMessageData.size()); stream<basic_array_source<char>> stream(input_source); boost::archive::binary_iarchive archive(stream); Utils::MensajeRed msg; archive >> msg; i_->playerLog->trace() << "NetMessage correctly read."; p.set_value(std::move(msg)); }); return message; }

在我的日志文件中，我在客户端获得以下内容：

[clientLog] [info] Client: Starting... [clientLog] [trace] User1234 connecting to localhost:10004 [clientLog] [trace] waiting to read message from server socket...

但我希望该日志的第三行会在[clientLog] [info] Connected to server.之后出现所以我的期望如下：

[clientLog] [info] Client: Starting... [clientLog] [trace] User1234 connecting to localhost:10004 [clientLog] [info] Connected to server. [clientLog] [trace] waiting to read message from server socket...

即＆＃34;连接到服务器＆＃34;应始终之前等待从服务器套接字读取消息...＆＃34;。

有谁知道发生了什么事？我以为strand_会保证执行顺序，但似乎我可能误解了一些东西。获得我想要的效果的正确解决方案是什么？

Answer 1

所以这里的问题是任务将按顺序启动，但链中的后续boost::asio::spawn spawn调用并不意味着第一个任务将在第二个任务之前完成。

第一个任务在第二个任务之前启动，只会发生

。

为了保持顺序，我只创建了一个在asyncConnectTo中的spawn中调用的协程，而不是产生两个不同的协同程序。通过这种方式，我确保第一个协程在第二个协程之前完成：

NetMessage Cliente::asyncReceiveMessageCoro(boost::asio::yield_context yield) {
    namespace ba = boost::asio;
    i_->playerLog->trace("waiting to read message from server socket...");
    boost::system::error_code ec{};
    boost::int64_t messageSize{};
    ba::async_read(
      socket_,
      ba::buffer(&messageSize, sizeof(boost::int64_t)),
      yield);

    i_->playerLog->trace() << "Client: Received message of "
                                   << messageSize << " bytes. Reading message...";

    std::vector<char> serverMessageData(messageSize);
    ba::async_read
       (socket_,
        ba::buffer(serverMessageData),
        yield);

    using namespace boost::iostreams;
    basic_array_source<char> input_source(&serverMessageData[0], serverMessageData.size());
    stream<basic_array_source<char>> stream(input_source);
    boost::archive::binary_iarchive archive(stream);
    Utils::MensajeRed msg;

    archive >> msg;
    i_->playerLog->trace() << "NetMessage correctly read.";
    return msg;
}

这个协程可以在最后链接：

std::future<NetMessage> Cliente::asyncConnectTo(std::string const & hostname,
                                          int port,
                                          std::string const & name) {
    using namespace std::literals;

    std::promise<NetMessage> msgProm;
    auto msg = msgProm.get_future();
    boost::asio::spawn
        (strand_,
         [this, name, port, hostname, p = std::move(msgProm)](boost::asio::yield_context yield) mutable {
            i_->playerLog->trace() << name << " connecting to " << hostname << ':'
                                   << port;
            Guinyote::Utils::connectWith
                (*this, std::move(hostname), port,
                 std::move(name), yield);

            i_->playerLog->info() << "Connected to server.";
            p.set_value(this->asyncReceiveCoro(yield));
        });
    runthread_ = std::thread([&] {
            try {
                i_->playerLog->info() << "Starting...";
                this->service_.run();
            }
            catch (std::exception & e) {
                std::cout << e.what() << std::endl;
            }
        });
    return msg;
}

我的旧asyncReceiveMessage只是spawn +调用asyncReceiveMessageCoro的组合。

混淆了boost :: asio :: yield在同一条链中的执行顺序

1 个答案: