首先，错误125是操作中止：所以这意味着（可能）一个cancel（）调用（或者IO对象的析构函数导致取消）。
这很正常
我已经煞费苦心地完成了你不完整的代码¹，并不容易看到你的问题：

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#include <boost/asio.hpp>
#include <boost/bind.hpp>
#include <iostream>

struct myclass {
    struct timeout_exception : std::runtime_error {
        timeout_exception(std::string const &msg) : std::runtime_error(msg) {}
    };

    enum {
        resultInProgress,
        resultTimeoutExpired,
        resultSuccess,
        resultError,
    } result = resultInProgress;

    std::string readStringUntil(std::string const &);
    struct ReadSetupParameters {
        ReadSetupParameters(std::string const &d = "") : delim{ d } {}
        std::string delim;
        bool fixedSize = false;
        char mutable data[1024];
        size_t size = sizeof(data);
    };

    void performReadSetup(const ReadSetupParameters &param);

    ReadSetupParameters setupParameters;
    boost::posix_time::time_duration timeout{ boost::posix_time::seconds(3) };
    boost::asio::io_service io;
    boost::asio::deadline_timer timer{ io };

    // more likely a serial port, but I'm not gonna bother mocking that:
    boost::asio::ip::tcp::socket port{ io };
    boost::asio::streambuf readData;
    size_t bytesTransferred;

    myclass() { port.connect({ {}, 6767 }); }

    void timeoutExpired(boost::system::error_code const &ec);
    void readCompleted(boost::system::error_code const &ec, size_t bytesTransferred);
};

std::string myclass::readStringUntil(const std::string &delim) {
    using namespace boost;

    setupParameters = ReadSetupParameters(delim);
    performReadSetup(setupParameters);

    if (timeout != posix_time::seconds(0))
        timer.expires_from_now(timeout);
    else
        timer.expires_from_now(posix_time::hours(100000));

    timer.async_wait(boost::bind(&myclass::timeoutExpired, this, asio::placeholders::error));

    result = resultInProgress;
    for (;;) {
        io.run_one();
        switch (result) {
        case resultSuccess: {
            timer.cancel();
            bytesTransferred -= delim.size(); // Don't count delim
            std::istream is(&readData);
            std::string result(bytesTransferred, '\0'); // Alloc string
            is.read(&result[0], bytesTransferred);      // Fill values
            is.ignore(delim.size());                    // Remove delimiter from stream
            return result;
        } break;
        case resultTimeoutExpired:
            port.cancel();
            std::cout << "timeout on readuntill" << std::endl;
            throw(timeout_exception("Timeout expired"));
            break;
        case resultError:
            timer.cancel();
            port.cancel();
            throw(boost::system::system_error(boost::system::error_code(), "Error while reading"));
        }
    }
}

/////////////////////////////////////////////////////////////////////////////

void myclass::performReadSetup(const ReadSetupParameters &param) {
    using namespace boost;
    if (param.fixedSize) {
        asio::async_read(port, asio::buffer(param.data, param.size),
                         boost::bind(&myclass::readCompleted, this, asio::placeholders::error,
                                     asio::placeholders::bytes_transferred));
    } else {
        asio::async_read_until(port, readData, param.delim,
                               boost::bind(&myclass::readCompleted, this, asio::placeholders::error,
                                           asio::placeholders::bytes_transferred));
    }
}

/////////////////////////////////////////////////////////////////////////////

void myclass::timeoutExpired(const boost::system::error_code &error) {
    if (!error && result == resultInProgress)
        result = resultTimeoutExpired;
}

/////////////////////////////////////////////////////////////////////////////

void myclass::readCompleted(const boost::system::error_code &error, const size_t bytesTransferred) {
    if (!error) {
        result = resultSuccess;
        this->bytesTransferred = bytesTransferred;
        return;
    }

#ifdef _WIN32
    if (error.value() == 995)
        return; // Windows spits out error 995
#elif defined(__APPLE__)
    if (error.value() == 45) {
        // Bug on OS X, it might be necessary to repeat the setup
        // http://osdir.com/ml/lib.boost.asio.user/2008-08/msg00004.html
        performReadSetup(setupParameters);
        return;
    }
#else // Linux
    if (error.value() == 125)
        return; // Linux outputs error 125
#endif

    result = resultError;
}

int main() {
    myclass absent;
    std::cout << "Ok: '" << absent.readStringUntil("Transferred") << "'\n";
}

注意事项：

• 看起来你基本上是在努力避免异步调用。这让事情变得笨拙。如果您只需要超时，请参阅Boost：：Asio synchronous client with timeout和boost：：asio + std：：future - Access violation after closing socket
• 你似乎没有意识到*read_until可以读取 * 超出 * 分隔符（它将读取 * 至少 * 直到并包括第一次看到分隔符）。你真的应该解释一下
• 您永远不会检查run_one()的返回值。如果返回0，则循环应该退出。不执行reset()而再次运行它将不会有任何效果。

为什么？

我的解决方法是：

case resultSuccess:
        m_timer.cancel();
        m_io.reset();
        break;//go to finalize timer spirious event
        //return;