How to avoid resource consumption

[Rocky651]

I am just a beginner in mutlithreading.
I have a main program that creates a single thread, which code looks like this:

MyThread
{
while (threadActive)
{
if (workToBeDone)
doTheWork();
}
return 0;
}

There is no need of a mutex because the variables used in 'doTheWork()' are local, only used there. The booleans 'threadActive' and 'workToBeDone' are set my the main program: when it sets 'threadActive' to false, the thread ends, and it sets 'workToBeDone' when the 'doTheWork' function needs to be called.

It works fine, but I have a problem:
When the thread is active, it takes 100% of the CPU for one of the cores, even if no work needs to be done and 'workToBeDone' remains false. The 'while' loop takes all the CPU. SO I thought about adding a 'Sleep' in the loop, but the problem is that it delays the invocation of 'doTheWork' when a work needs to be done (this is a problem because it is related to real-time graphics).

Is there a solution to avoid taking 100% of the CPU when no work has to be done and the thread just loops?

Thank you,
Eric

[ahoodin]

You could try something like this:

  int nTime = 100;//play with this value
  while (1)
  {
     if (work)
     {
        //do your work here
     }
     else
     {
       Sleep(nTime);  //wont sleep if there is work to be done                   
     }
  }
}

Although this is pretty rudimentary.

[Rocky651]

This would work, but if 'work' is set to true while the thread is sleeping, there can be a delay of 100 ms (in the worst case) before the work begins. This is not acceptable because of the constraints of my application.

Thanks for your help !!
Eric

[Codeplug]

You typically create a manual reset event for "thread exit", and either a manual reset or auto reset event for "do work". Then the thread uses WaitForMultipleObjects() to detect when the events are in a signaled state.
http://msdn.microsoft.com/en-us/libr...15(VS.85).aspx

gg

[ahoodin]

I did say that you could change the value of the nTime variable. On Windows XP you can get about 10ms and on Vista 1ms sleeps. Those are the perspective quantums. I agree with codeplug on the waitformultipleobjects(), although you should consider how time critical your code really is.

This would work, but if 'work' is set to true while the thread is sleeping, there can be a delay of 100 ms (in the worst case) before the work begins. This is not acceptable because of the constraints of my application.

Thanks for your help !!
Eric

[Rocky651]

You typically create a manual reset event for "thread exit", and either a manual reset or auto reset event for "do work". Then the thread uses WaitForMultipleObjects() to detect when the events are in a signaled state.
http://msdn.microsoft.com/en-us/libr...15(VS.85).aspx

gg

Indeed, using WaitForSingleObject to wait for the trigger (an event) that starts the work is much better. The CPU usage is now optimal and my thread is as fast as before !!

Thank for your help !!
Eric

[Lindley]

In general event-based programming is better than busywaiting, yes. Another way to accomplish this would be to have a condition variable which the loop waits on, that gets signaled whenever it's time to move on to another task.