How Java precise sleep under 1ms-CodePudding

I'm working on swing & graphic2D, And I ran into some issue, How to precise sleep?

Because for 144 or 240 fps monitor , ms is too long. With 4.1667ms Thread.sleep will cause very unstable result and time been scaled. Question is is there some way to real sleep under 1ms?

I did some research and found something like this Thread.Sleep for less than 1 millisecond

And according to the post, Event sleep(1) will not sleep accurate 1ms, As my test there is 100 times result:

None of them is close, At least will cause 10ms, And some of them even more then 20ms!

And 20ms is unacceptable for even 60FPS monitor. Because 16.67ms is the frame rate.

And I seek into Thread.sleep

public static void sleep(long millis, int nanos)
throws InterruptedException {
    if (millis < 0) {
        throw new IllegalArgumentException("timeout value is negative");
    }

    if (nanos < 0 || nanos > 999999) {
        throw new IllegalArgumentException(
                            "nanosecond timeout value out of range");
    }

    if (nanos >= 500000 || (nanos != 0 && millis == 0)) {
        millis  ;
    }

    sleep(millis);
}

I can't even believe java just treat nano second as ms if longer then 0.5ms, And other things like TimeUnit.sleep or Object.wait just call thread.sleep or convert into ms internal. So is that mean in windows or linux or any non-realtimeOS, There is no way to precise sleep? How game engine do that?

CodePudding user response：

Game engines relies on Delta time for making games frame rate independent, Delata time is nothing but elapsed time between the last frame and current frame. You can measure delta time as

DeltaTime = 1/FPS

So you can use this variable to make the game independent by multiplying this with your game variables, for example if you want to move a player independent of Frame rate you would do something like

Player.position = Player.position MovementSpeed * DeltaTime

If initial position = 10 , MovementSpeed = 1 If FPS = 60, DeltaTime = 0.016666667 then distance after 1 second is

Player.position = 10 1 * (0.016666667*60) which is '11' (Here it's multiplied with 60 to simply acomodate the fact that same calculation will run for 60 times when game is running at 60 FPS so Player.position will be updated by 0.016666666 for 60 Times)

If FPS = 30 , DeltaTime = 0.03333 then distance moved after 1 seconds is Player.position = 10 1*(0.03333*30) which is '11' So game can run independent of Frame Rates

You could try to calculate DeltaTime like:

//In main Game loop
current time = getSystemTime()
Delta time = current time - old time 
old time = current time // save old time for next loop

CodePudding user response：

You need not sleep yourselvies. You should run your code as fast as possible. The monitor will help you synchronize your video output and you don't have to keep your code waiting for the monitor.

CodePudding user response：

Thread.sleep has 2 methods, one of which accepts nanoseconds.

 Thread.sleep(long millis, int nanos)

So Thread.sleep(1); is equal to Thread.sleep(0,1000000);

So if you want to sleep half of a milisecond, use

Thread.sleep(0,500000)

Helpful Links:-

Add a decimal millisecond delay to Java code

Can a Thread sleep for less than half milli seconds in Java/ Other language?