WaitableTimer in C++

This is an example code for calling a waitable timer. This is a good way to wait for a timer event without using CPU (thread blocks). There is a small trick in the code. It’s hard to create a FILETIME properly so I create a SYSTEMTIME (and set it according to my needs), convert it to FILETIME, finally I cast that to LARGE_INTEGER* (to fulfill the needs of SetWaitableTimer).

I set the timer to autoreset, so it will restart counting after firing the event (counts again and again). The first event (“CALLED”) occurs after 3 secs, the subsequent events occur after 2 secs.

The WaitForSingleObject blocks until a timer event is fired. I break the loop after 5 events, stop the timer and delete the timer handle.

stdafx.h

#pragma once

#include "targetver.h"

#include <stdio.h>
#include <tchar.h>
#include <iostream>
#include <Windows.h>

using namespace std;

WaitableTimer.cpp

#include "stdafx.h"

int _tmain(int argc, _TCHAR* argv[])
{
    int count = 0;    // Iteration counter

    HANDLE hTimer = NULL;    // WaitableTimer handle
    hTimer = CreateWaitableTimer(    // Create waitable timer
        NULL,
        FALSE,    // Autoreset --> timer restarts counting after event fired
        NULL);

    SYSTEMTIME time;        // System time structure
    GetSystemTime(&time);    // Curren time
    time.wSecond += 3;        // Wait 3 sec

    FILETIME ftime;    // File time (expected by SetWaitableTimer)
    SystemTimeToFileTime(&time, &ftime);    // Convert system to file time


    if(!SetWaitableTimer(    // Set waitable timer
        hTimer,    // Timer handle
        reinterpret_cast<LARGE_INTEGER*>(&ftime),    // Convert file time to large integer
        2000,    // Period time, fire again after 2 sec
        NULL,
        NULL,
        0))
    {
            cout << "SetWaitableTimer failed" <<  GetLastError() << endl;
    };

    
    while(WaitForSingleObject(hTimer, 5000) == WAIT_OBJECT_0){    // Wait for timer event
        cout << "CALLED " << ++count << endl;
        if(count+1 > 5){    // Exit after 5 events
            break;
        }
    }
        
    CancelWaitableTimer(hTimer);    // Stop timer
    CloseHandle(hTimer);            // Delete handle

    return 0;
}

See source code: http://code.google.com/p/artur02/source/browse/trunk/CPP/WaitableTimer/WaitableTimer.cpp

Waitable timer objects: http://msdn.microsoft.com/en-us/library/ms687012(VS.85).aspx
CreateWaitableTimer function: http://msdn.microsoft.com/en-us/library/ms682492(v=VS.85).aspx
SetWaitableTimer function: http://msdn.microsoft.com/en-us/library/ms686289(v=VS.85).aspx
Systemtime structure: http://msdn.microsoft.com/en-us/library/ms687008(v=VS.85).aspx
Usage example: http://msdn.microsoft.com/en-us/library/ms687008(v=VS.85).aspx