does java timer start its own thread?

[robust agate]

title

[harsh violet]

<@&987246399047479336> please have a look, thanks.

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Title

No, Java Timer does not start its own thread. Instead, it uses a single background thread that is shared among all Timer instances. This means that if you have multiple Timer instances running, they will all share the same thread for executing their tasks.

This design choice was made to reduce the overhead of creating and managing multiple threads for each Timer instance. However, it also means that if a task takes a long time to execute or if one Timer instance blocks the shared thread, it can affect the execution of tasks in other Timer instances.

If you need more control over threading behavior or need to run tasks in parallel, you may want to consider using a different concurrency mechanism such as Executors in the java.util.concurrent package.

Overall, while Java Timer provides a simple way to schedule tasks to run at specific times or intervals, it is important to be aware of its threading behavior and limitations when designing your applications.

- AI generated response

[robust agate]

that is intresting bc I am being yelled at by my code for wrong thread

Thread.startVirtualThread(() -> physicsEngine = new PhysicsEngine()); I have this in my main class

and the constructor of physics engine has

        new Timer().schedule(new TimerTask() {
            long lastRan = System.nanoTime();
            @Override
            public void run() {
                long diff = System.nanoTime() - lastRan;
                float deltaTime = diff / 1_000_000_000f;

                lastRan = System.nanoTime();
                update(deltaTime);
            }
        }, 1L, 1L);```

it yells for using wrong thread everytime I update the engine

can it be because the variable is in main class? which is on main thread

[remote temple]

Which framework ? Swing ? JavaFX ? Other ?

[robust agate]

no its a lib named bullet

[remote temple]

Yes Timer or things like ScheduledExecutor use their own thread

[robust agate]

fucking knew it

is there a way to force timer to use my current thread? or is there an alternative

[remote temple]

no, it simply can't use your thread

otherwise the timer wouldn't work

[robust agate]

how do i make it run the method then?

[remote temple]

a framework would usually share a method when you can give it code to execute in their thread

With Swing, you have SwingUtilities.invokeLater, with JavaFX, you have Platform.runLater, etc

[robust agate]

it just needs the native library loaded on that thread too

    public void update(float timeInterval, int maxSteps, boolean doEnded,
            boolean doProcessed, boolean doStarted) {
        assert Validate.nonNegative(timeInterval, "time interval");
        assert Validate.nonNegative(maxSteps, "max steps");

        if (NativeLibrary.jniEnvId() != jniEnvId()) {
            logger.log(Level.WARNING, "invoked from wrong thread");
        }

        long spaceId = nativeId();
        assert accuracy > 0f : accuracy;
        stepSimulation(spaceId, timeInterval, maxSteps, accuracy, doEnded,
                doProcessed, doStarted);
    }```

maybe I can just load library there too?

[remote temple]

wdym

also note that frameworks tend to give you a special timer which work with them

Swing has Timer, and JavaFX has Animation

for example

[robust agate]

I am gonna have to check..

https://stephengold.github.io/Libbulletjme/javadoc/master/

I cant really find anything on their api

is there any other way?

[remote temple]

what are you trying to do requiring this ?

[robust agate]

to keep updating the physics space

[remote temple]

does this lib has a update method which is called automatically ?

[robust agate]

nope

you need to call update yourself if u wanna update

this is going to be hard

[remote temple]

@robust agate can you show me the error please ?

[robust agate]

does not have a stack trace

its their custom error for thread saftey ig

I can try and catch if u want

[remote temple]

move the physics in the correct thread then

instead of creating a timer

do the timer yourself with Thread.sleep

[robust agate]

should I just make the class extend TimerTask?

[remote temple]

no

[robust agate]

how would that work

[remote temple]

you do a while loop

and you sleep for a certain time

[robust agate]

which would be 50ms

[remote temple]

if you want 200fps yes

[robust agate]

I am just updating it every 1 tick

[remote temple]

but what is one tick ?

you want to update each 1000/tps ms

[robust agate]

1 tick = 1 second /20

[remote temple]

so 1000/20=50

ms

[robust agate]

small error.

[remote temple]

?

[robust agate]

        long lastRan = System.nanoTime();
        while (1 == 1) {
            Thread.sleep(50);
            long diff = System.nanoTime() - lastRan;
            float deltaTime = diff / 1_000_000_000f;

            lastRan = System.nanoTime();
            update(deltaTime);
        }```

yeah

do u just mean this?

it looks like its not giving any error

[remote temple]

why 1==1, you know that true exists right ?

also delta here is 50

always

and you are not updating lastRan

[robust agate]

I am?

[remote temple]

well actually, it's more

[remote temple]

you are not

[robust agate]

lastRan = System.nanotime

[remote temple]

ah my bad

but you system has still a problem

which is that you wait for more than 50ms

[robust agate]

hmm

java.lang.NullPointerException: Cannot invoke "io.github.unjoinable.physics.PhysicsEngine.addObject(io.github.unjoinable.physics.PhysicsObject)" because "physicsEngine" is null

I legit

private static volatile PhysicsEngine physicsEngine;

        Thread.startVirtualThread(() -> {
            try {
                physicsEngine = new PhysicsEngine();
            } catch (InterruptedException e) {
                throw new RuntimeException(e);
            }
        });```

thats all done on the main thread

[remote temple]

why did you assigned it in a thread ?

[robust agate]

because I am trying to run the engine on a seperate thread

[remote temple]

but why ?

[robust agate]

So if it gets laggy it does not block main thread

[remote temple]

and what is the main thread doing ?

[robust agate]

running the minecraft server

[remote temple]

huh

wait

what are you trying to do ?

[robust agate]

Running Physics Engine alongside Minecraft

to provide accurate physics in minecraft

[remote temple]

why can't you run it during minecraft ticks ?

[robust agate]

good question

I thought it would be more efficient and better

What if the physics space gets too populated and starts lagging server

[remote temple]

but how are you going to link minecraft ticks and the lib ticks ?

they don't happen at the same time

[robust agate]

why do u think I update it every 1 tick

[remote temple]

they don't happen at the same time

[robust agate]

how?

[remote temple]

Because you never made them happen at the same time ?

[robust agate]

this is confusing

i mean they dont really need to happen at same time do they

[remote temple]

depends

how are you linking them ?

[robust agate]

every entity has an update method

which automatically teleports the mc entity by getting coords from physics space

[remote temple]

what if minecraft ticks and your engine ticks don't happen at the same rate ? for example because of lag

[robust agate]

I have not thought about that yet BUT

I think concurrency is bad now

I can just get instance thread from minecraft and run it on that

[remote temple]

anyway

why don't you create your physics just before going in the sleep loop and in the same thread as the sleep loop ?

[robust agate]

what do u mean

[remote temple]

why don't you create the physics engine in the same thread as the while sleep loop ?

[robust agate]

i dont know

[remote temple]

then do it

[robust agate]

ooh I get it..thank u