Timer & Thread

[Kasi P.Pillai]

Sir,

I'm developing a Real time application program.
Based on the time i'm taking data from the database &
processing. So once the program is started, all the processes
are executed on the basis of time. So i want to get the time
at any time during the exexution. If i'm using the SetTimer() function i can't get that.
I'm using a PCI card(I/O) to send & recieve signals from
the external devices. I want to poll each external devices.
No i'm planning to use thread for that. Is there any other method for that.

kasi

[Andreas Masur]

Well...which operating system you are using? It looks like you are trying to achieve this under Windows.

First of all Windows is far away from being real-time. So, if you definitely need absolute real-time you should consider using such an operating system like QNX.

Nevertheless there are much better solutions under Windows than using the WM_TIMER messages like waitable timers or multimedia timers...

The following is a sample how to use waitable timers. They will delay execution by 10 seconds in the following...

#include <iostream>
#include <windows.h>
#include <conio.h>

int main()
{
  HANDLE hTimer = NULL;
  LARGE_INTEGER liTime;

  liTime.QuadPart=-100000000;

  // Create a waitable timer.
  hTimer = ::CreateWaitableTimer(NULL, TRUE, "WaitableTimer");
  if(!hTimer)
  {
    std::cout << "Could not create waitable timer (Error "
              << ::GetLastError() << ")" << std::endl;
    ::Sleep(5000);
    return -1;
  }

  std::cout << "Wait for 10 seconds..." << std::endl;

  // Set timer
  if(!::SetWaitableTimer(hTimer, &liTime, 0, NULL, NULL, 0))
  {
    std::cout << "Could not set waitable timer (Error "
              << ::GetLastError() << std::endl;
    ::Sleep(5000);
    return -1;
  }

  // Wait for timer
  if(::WaitForSingleObject(hTimer, INFINITE) != WAIT_OBJECT_0)
    std::cout << "Could not wait for timer object (Error "
              << ::GetLastError() << std::endl;
  else
    std::cout << "Time elapsed" << std::endl;

  // Wait for keystroke
  _getch();

  return 0;
}

For additional information you might take a look at http://www.codeproject.com/system/timers_intro.asp. It is a very comprehensive timer tutorial.