如何使用 Boost 库创建 TimerHandler

Question

我正在开发一个使用 C++ 的项目。

我希望在指定时间后调用 TimerHandler，但同时我不想阻塞当前线程或以下代码中 io.run() 之后的任何代码：

#include <iostream>
#include <string>
#include <boost/format.hpp>
#include <boost/asio.hpp>
#include <boost/bind.hpp>
#include <boost/date_time/posix_time/posix_time.hpp>

class TimerTest
{
public:
    static void PrintOutTimerHandler(const boost::system::error_code&, const std::string& message)
    {
        std::cout << "PrintOutTimerHandler called: " << ", message: " << message << std::endl;
    }

    void run()
    {
        boost::asio::io_service io;
        boost::asio::deadline_timer dt(io, boost::posix_time::seconds(5));

        std::cout << "Start:\t" << std::endl;

        dt.async_wait(boost::bind(PrintOutTimerHandler, boost::asio::placeholders::error, std::string("here is the message")));

        // Do some job here
        for (int i = 0; i < 1000000; ++i)
            ++i, --i;

        std::cout << "End:\t" << std::endl;

        io.run();

        std::cout << "When to reach here 1: " << std::endl;
    }
};

int main()
{
    TimerTest tt;
    tt.run();

    std::cout << "When to reach here 2: " << std::endl;

    return 0;
}

/* Current output:
Start:
End:
PrintOutTimerHandler called: , message: here is the message
When to reach here 1:
When to reach here 2:
 */

/* Expected output:
Start:
End:
When to reach here 1:
When to reach here 2:
PrintOutTimerHandler called: , message: here is the message
 */

我想我已经说清楚了。我的问题是：

• 如果不这样做就可以解决这个问题 引入新线程，例如 Flex ActionScript，这是最好的，但是 我想不是（我想 ActionScript 是 使用隐藏线程）；
• 如果我们必须 引入一个额外的线程来执行 工作，你介意写下 我的伪代码？

谢谢。

彼得

Answer 1

这是一个例子。在单独的线程中运行 io_service

asio::io_service io_service;
asio::thread t(boost::bind(&asio::io_service::run, &io_service));

或在线程组中运行它

boost::thread_group threads;
for (std::size_t i = 0; i < my_thread_count; ++i)
    threads.create_thread(boost::bind(&asio::io_service::run, &io_service));

请记住，主线程应该始终运行，因为当它存在时，生成的所有线程也将退出。

我希望这有帮助。

Answer 2

我误解了 OrcunC 所说的，但实际上他是对的。以下是修改后的版本供您参考：

#include <iostream>
#include <string>
#include <boost/format.hpp>
#include <boost/asio.hpp>
#include <boost/bind.hpp>
#include <boost/thread.hpp>
#include <boost/date_time/posix_time/posix_time.hpp>

class TimerTest
{
public:
    static void PrintOutTimerHandler(const boost::system::error_code&, const std::string& message)
    {
        std::cout << "PrintOutTimerHandler called: " << ", message: " << message << std::endl;
    }

    TimerTest(unsigned int timeout)
        : dt(io, boost::posix_time::milliseconds(timeout))
    {
    }

    void run()
    {
        std::cout << "Start:\t" << std::endl;

        dt.async_wait(boost::bind(PrintOutTimerHandler, boost::asio::placeholders::error, std::string("here is the message")));

        boost::thread thrd(boost::bind(&boost::asio::io_service::run, &io));

        // Do some job here
        for (int i = 0; i < 1000000; ++i)
            ++i, --i;

        std::cout << "End:\t" << std::endl;

        std::cout << "When to reach here 1: " << std::endl;
    }

    boost::asio::io_service     io;
    boost::asio::deadline_timer dt;
};

int main()
{
    TimerTest tt(5000);
    tt.run();

    std::cout << "When to reach here 2: " << std::endl;

    // Keep the main thread active for testing purpose. Otherwise,
    // once the TimerTest object is destroyed when exiting the main() function,
    // the sub thread spawed in tt.run() will also exit;
    Sleep(10000);
}

/* Current output and Expected output:
Start:
End:
When to reach here 1:
When to reach here 2:
PrintOutTimerHandler called: , message: here is the message
 */