demo using 100% CPU

Java 2D
#1

Hi there! I have coded a small demo, but it is using 100% of the CPU. How can I avoid this? Below is the run() method

I am running on win2000 and FPS=60. Is Thread.yield() not working or I missed something?


final int FRAME_LENGTH = 1000 / FPS;
            long startTime = System.currentTimeMillis();
            int frameCount = 0;
            System.out.println(FRAME_LENGTH);
            while (!this.quit) {
                  this.paint(this.getGraphics());
                  frameCount++;
                  while ((System.currentTimeMillis() - startTime) / FRAME_LENGTH < frameCount) {
                        System.out.println("fc=" + frameCount + " elapsed="
                                    + ((System.currentTimeMillis() - startTime) * 1000)
                                    + " fps=" + (float) frameCount
                                    / (System.currentTimeMillis() - startTime) * 1000);
                        frameCount = 0;
                        Thread.yield();
                  }
            }
#2

yield() changes threads. Thus, if your thread is the only one that is ready to run, you’ll be back immediately.

Thread.sleep()?

#3

That’s right. And there’s nothing intrinsically wrong with using 100% CPU if you’re being kind to other processes by yielding.

Cas :slight_smile:

#4

I have re-designed my demo and in the main run() loop of the demo as follows:


            int delayPerFrame = 1000/60;
            PreciseTimer preciseTimer = new PreciseTimer(delayPerFrame);             
            while (!this.quit) {
                  preciseTimer.start();
                  this.paint(this.getGraphics());
                  try{
                        Thread.sleep(delayPerFrame-preciseTimer.getMilliSeconds());
                  }catch(Exception e) {}
                  preciseTimer.endTimer();
            }

Here is the code for PreciseTimer:


      private class PreciseTimer implements Runnable{

            private Thread preciseTimerThread = new Thread(this, "precise");
            private long milliSeconds=0;
            private boolean endTimer = false;
            private int maxMilliSeconds=0;

            public PreciseTimer()
            {
            preciseTimerThread.start(); 
            }

            public PreciseTimer(int max)
            {
            maxMilliSeconds=max;
            preciseTimerThread.start(); 
            }

            public void start(){
            milliSeconds=0;
            }

            public long getMilliSeconds(){
            if (milliSeconds>maxMilliSeconds){milliSeconds=maxMilliSeconds;}
            return (milliSeconds);
            }

            public void endTimer(){
            endTimer=true;
            }



            public void run(){
            while (!endTimer){ 
            milliSeconds++;
            try{preciseTimerThread.sleep(1);}catch(java.lang.InterruptedException e){}
            }

            }

            }

Now the question: What about this code? Is this valid code to lock my demo at 60fps?

#5

Is this valid code to lock my demo at 60fps?

Theoretically, yes.

However, sleep is only accurate down to ~5msec (on windows at least).

If you need accurate throtteling and you still want to use sleep you can check if the time to waste is >5msec and sleep then.

Eg something like this (change accordingly):


public static void sync2b(long fps) //hz+1
{
      long gapTo = Sys.getTimerResolution() / fps + timeThen;
      timeNow = Sys.getTime();

      while(gapTo > timeNow+timeLate)
      {
            if(gapTo > timeNow+timeLate+5000L)
                  Thread.sleep(5);
            else
                  Thread.yield();
            timeNow = Sys.getTime();
      }

      if(gapTo<timeNow)
            timeLate = timeNow-gapTo;
      else
            timeLate = 0;

      timeThen = timeNow;
}