6

当你调用expires_from_now()一个正在运行的定时器时，定时器被取消，并调用一个新的定时器。因此调用关联的处理程序。在处理程序中很容易区分取消的计时器和过期的计时器。然而，我想知道，是否有办法区分过期和重新触发的计时器。在这两种情况下，处理程序都使用 error_code 调用operation_aborted。或者我可能遗漏了一些细节。

下面的代码生成以下输出：

20120415 21:32:28079507 Main: Timer1 set to 15 s.    
20120415 21:32:28079798 Main: Timer1 set to 12 s.    
20120415 21:32:28079916 Handler1: Timer 1 was cancelled or retriggered.    
20120415 21:32:40079860 Handler1: expired.

这表明处理程序无法为取消的处理程序实现操作，因为重新触发计时器将调用相同的处理程序并因此执行相同的操作。这可能不是预期的行为。

#include <boost/asio.hpp> 
#include <boost/thread.hpp> 
#include <boost/date_time/posix_time/posix_time.hpp>
#include <boost/date_time/posix_time/posix_time_io.hpp>
#include <iostream> 

using namespace boost::posix_time;
using namespace std;

void handler1(const boost::system::error_code &ec) 
{ 
    if (ec == boost::asio::error::operation_aborted)
    {
        cout << microsec_clock::local_time() << " Handler1: Timer was cancelled or retriggered." << endl; 
    }
    else
    {
        cout << microsec_clock::local_time() << " Handler1: Timer expired." << endl; 
    }
} 

boost::asio::io_service io_service1; 

void run1() 
{ 
    io_service1.run(); 
} 

int main() 
{ 
    time_facet *facet = new time_facet("%Y%m%d %H:%M:%S%f");
    cout.imbue(locale(cout.getloc(), facet));

    boost::asio::deadline_timer timer1(io_service1, seconds(15)); 
    timer1.async_wait(handler1); 
    cout << microsec_clock::local_time() << " Main: Timer1 set to 15 s." << endl; 
    // now actually run the timer
    boost::thread thread1(run1); 
    timer1.expires_from_now(seconds(12));
    cout << microsec_clock::local_time() << " Main: Timer1 set to 12 s." << endl; 
    // here the timer is running, but we need to reset the deadline
    timer1.async_wait(handler1); 
    thread1.join();   // wait for thread1 to terminate 
}
4

2 回答 2

4

我建议创建一个类来包装deadline_timer使用组合。取消它时，设置一个标志以记住它已被取消。在处理程序中，重置标志。调用expires_from_now()时不要设置标志。

#include <boost/asio.hpp> 
#include <boost/thread.hpp> 
#include <boost/date_time/posix_time/posix_time.hpp>
#include <boost/date_time/posix_time/posix_time_io.hpp>
#include <iostream> 

class Timer
{
public:
    Timer(
            const std::string& name,
            boost::asio::io_service& io_service
         ) :
        _name( name ),
        _timer( io_service ),
        _cancelled( false )
    {
        _timer.expires_from_now( boost::posix_time::seconds(0) );
        this->wait();
    }

    void wait()
    {
        _timer.async_wait(
                boost::bind(
                    &Timer::handler,
                    this,
                    boost::asio::placeholders::error
                    )
                );
    }

    void cancel() { 
        _cancelled = true;
        _timer.cancel(); 
    }

    void restart() {
        _timer.expires_from_now( boost::posix_time::seconds(5) );
    }

private:
    void handler(
            const boost::system::error_code& error
            )
    {
        if ( !error ) {
            std::cout << _name << " " << __FUNCTION__ << std::endl;
            _timer.expires_from_now( boost::posix_time::seconds(5) );
            this->wait();
        } else if ( error == boost::asio::error::operation_aborted && _cancelled ) {
            _cancelled = false;
            std::cout << _name << " " << __FUNCTION__ << " cancelled" << std::endl;
        } else if ( error == boost::asio::error::operation_aborted ) {
            std::cout  << _name << " " << __FUNCTION__ << " retriggered" << std::endl;
            this->wait();
        } else {
            std::cout << "other error: " << boost::system::system_error(error).what() << std::endl;
        }
    }

private:
    const std::string _name;
    boost::asio::deadline_timer _timer;
    bool _cancelled;
};

int
main()
{
    boost::asio::io_service ios;
    Timer timer1( "timer1", ios );
    Timer timer2( "timer2", ios );

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

    sleep( 3 );
    std::cout << "cancelling" << std::endl;
    timer1.cancel();
    timer2.restart();

    thread.join();
}

示例会话

macmini:stackoverflow samm$ ./a.out
timer1 handler
timer2 handler
cancelling
timer1 handler cancelled
timer2 handler retriggered
timer2 handler
^C
macmini:stackoverflow samm$
于 2012-04-16T02:27:51.330 回答
0

我不知道任何方法，并且可能没有好的方法来做到这一点（文档中没有任何内容说您可以区分这两种情况）。

我相信这是有目的的。设置deadline_timer为新的到期时间，取消任何以前的处理程序，因为：

  • 有时很难判断计时器是否已经在等待，因此当您设置到期时间时，很难判断究竟会发生什么；
  • 这是防止调度事件运行两次的简单方法，需要以特殊方式处理另一个错误代码更容易出错。
于 2012-04-15T19:58:25.640 回答