c++ - 为什么 boost asio 函数 expires_from_now() 取消 deadline_timer？

Question

当我尝试获取(未设置!)当前到期时间时使用 boost expires_from_now() 似乎实际上取消了计时器， 但它实际上按预期运行，但最终没有调用处理程序。

或者换句话说，当使用 expires_from_now() 访问 deadline_timer 时 它会立即调用处理程序，并且在它过期时不会调用处理程序。

请考虑以下代码和相应的输出:

#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)
    {
        std::cout << microsec_clock::local_time() << " Handler1: Timer 1 was cancelled or retriggered." << std::endl; 
    }
    else
    {
        std::cout << microsec_clock::local_time() << " Handler1: expired." << std::endl; 
    }
} 

boost::asio::io_service io_service1; 

class Mytimer {
public:
    Mytimer();
    void startTimer();
    void runTimerThread();
    bool isRunning();
private:
    bool m_isRunning;
    boost::asio::deadline_timer* m_pTimer;
    boost::thread* m_pThread;
};

Mytimer::Mytimer()
  : m_pTimer(NULL),
    m_pThread(NULL)
{
    m_pTimer = new boost::asio::deadline_timer(io_service1); 
    m_pTimer->async_wait(handler1); 
}

void Mytimer::runTimerThread()
{
    io_service1.run();
}

void Mytimer::startTimer()
{
    m_pThread = new boost::thread(&Mytimer::runTimerThread, this);
    m_pTimer->expires_from_now(boost::posix_time::seconds(10));
}

bool Mytimer::isRunning()
{

    time_duration td = m_pTimer->expires_from_now();
    if (td.total_seconds() > 0)
    {
        return true;
    }
    return false;
}

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

    cout << microsec_clock::local_time() << " before timer construction" << endl;
    Mytimer timer;
    cout << microsec_clock::local_time() << " before startTimer()" << endl;
    timer.startTimer();
    cout << microsec_clock::local_time() << " IsRunning: " << timer.isRunning() << endl;
    for (int i = 0; i <= 20; i++)
    {
        sleep(1);
        cout << microsec_clock::local_time() << " IsRunning: " << timer.isRunning() << endl;
    }
} 

20120412 22:41:45689235 before timer construction
20120412 22:41:45689514 before startTimer()
20120412 22:41:45689619 IsRunning: 1
20120412 22:41:45689693 Handler1: Timer 1 was cancelled or retriggered.
20120412 22:41:46689792 IsRunning: 1
20120412 22:41:47689994 IsRunning: 1
20120412 22:41:48690179 IsRunning: 1
20120412 22:41:49690375 IsRunning: 1
20120412 22:41:50690530 IsRunning: 1
20120412 22:41:51690712 IsRunning: 1
20120412 22:41:52690884 IsRunning: 1
20120412 22:41:53691069 IsRunning: 1
20120412 22:41:54691236 IsRunning: 0
20120412 22:41:55691428 IsRunning: 0
20120412 22:41:56691614 IsRunning: 0
20120412 22:41:57691810 IsRunning: 0
20120412 22:41:58692001 IsRunning: 0
20120412 22:41:59692193 IsRunning: 0
20120412 22:42:00692364 IsRunning: 0
20120412 22:42:01692542 IsRunning: 0
20120412 22:42:02692706 IsRunning: 0
20120412 22:42:03692886 IsRunning: 0
20120412 22:42:04693071 IsRunning: 0
20120412 22:42:05693267 IsRunning: 0
20120412 22:42:06693465 IsRunning: 0

Answer 1

When I try to get (not set!) the current expiry time using boost expires_from_now() is seems to actually cancel the timer, yet it actually runs as expected, but does finally not call the handler.

这个假设是不正确的。当您创建 deadline_timer

时

m_pTimer = new boost::asio::deadline_timer(io_service1);
m_pTimer->async_wait(handler1);

您已经告诉它立即过期。然后，当您启动 io_service

时

m_pThread = new boost::thread(&Mytimer::runTimerThread, this);

你随后调用

m_pTimer->expires_from_now(boost::posix_time::seconds(10));

作为文档 describes clearly , 这将取消任何未完成的处理程序，强调是我的

This function sets the expiry time. Any pending asynchronous wait operations will be cancelled. The handler for each cancelled operation will be invoked with the boost::asio::error::operation_aborted error code.

要解决此问题，请按如下方式更改您的 Mytimer::startTimer() 方法

--- timer4.cc.orig  2012-04-13 11:18:47.000000000 -0500
+++ timer4.cc   2012-04-13 11:16:54.000000000 -0500
@@ -1,4 +1,3 @@
-
 #include <boost/asio.hpp> 
 #include <boost/thread.hpp> 
 #include <boost/date_time/posix_time/posix_time.hpp>
@@ -39,7 +38,6 @@
     m_pThread(NULL)
 {
     m_pTimer = new boost::asio::deadline_timer(io_service1); 
-    m_pTimer->async_wait(handler1); 
 }

 void Mytimer::runTimerThread()
@@ -49,8 +47,9 @@

 void Mytimer::startTimer()
 {
-    m_pThread = new boost::thread(&Mytimer::runTimerThread, this);
     m_pTimer->expires_from_now(boost::posix_time::seconds(10));
+    m_pTimer->async_wait(handler1); 
+    m_pThread = new boost::thread(&Mytimer::runTimerThread, this);
 }

 bool Mytimer::isRunning()

这会导致预期的行为

mbp:stackoverflow samm$ ./a.out
20120413 11:17:22922529 before timer construction
20120413 11:17:22923155 before startTimer()
20120413 11:17:22923530 IsRunning: 1
20120413 11:17:23924702 IsRunning: 1
20120413 11:17:24925971 IsRunning: 1
20120413 11:17:25927320 IsRunning: 1
20120413 11:17:26928715 IsRunning: 1
20120413 11:17:27929969 IsRunning: 1
20120413 11:17:28930601 IsRunning: 1
20120413 11:17:29931843 IsRunning: 1
20120413 11:17:30933098 IsRunning: 1
20120413 11:17:31934366 IsRunning: 0
20120413 11:17:32923594 Handler1: expired.
20120413 11:17:32934692 IsRunning: 0
20120413 11:17:33935922 IsRunning: 0
20120413 11:17:34936638 IsRunning: 0
20120413 11:17:35937905 IsRunning: 0
20120413 11:17:36939133 IsRunning: 0
20120413 11:17:37940407 IsRunning: 0
20120413 11:17:38941043 IsRunning: 0
20120413 11:17:39942319 IsRunning: 0
20120413 11:17:40942662 IsRunning: 0
20120413 11:17:41943989 IsRunning: 0
20120413 11:17:42945284 IsRunning: 0
20120413 11:17:43946555 IsRunning: 0
mbp:stackoverflow samm$