Java “pulse” between threads

Question

I have two threads. One runs a simulation and one runs a UI.

In the UI, it is possible to trigger a "tick" of the simulation. There are a few constraints:

• Ticks run on the simulation thread
• Each tick takes a bit of time to complete.
• When the user asks for n ticks, n ticks should be completed, even if they are requested during the execution of a tick.

To manage the triggering of ticks between threads, I have created a Pulse class. Here it is:

public final class Pulse {

    private final Object Lock = new Object();

    private volatile int count;

    public Pulse() {

        super();

        count = 0;
    }

    public void pulse() {

        synchronized (Lock) {

            count++;

            Lock.notifyAll();
        }
    }

    public void waitForPulse() throws InterruptedException {

        synchronized (Lock) {

            while (count == 0) {

                Lock.wait();
            }

            count--;
        }
    }
}

A single Pulse instance is shared between the UI and simulation threads.

In the UI thread I would have something like:

void onTickRequested() {

    simulationPulse.pulse();
}

And in the simulation thread I have something like:

while (isRunningSimulation) {

    myPulse.waitForPulse();

    tick();
}

Will my code work as expected? Is it thread-safe?

Answer 1

Good code! Just a few points:

1. super();

   This line of code is automatically put in by the compiler and is unnecessary to write it yourself. If it is a habit that you have a hard time breaking, you may leave it, as it does not compromise speed, but I would leave it out, as it does clutter code slightly.

2. Over-spacing

   Though spacing is good, too much space makes code hard to read as well. Your spacing is good, with one thing: you have a space between each line. Maybe it helps you, but I find it difficult to read.

   Compare:

   public final class Pulse {
   
       private final Object Lock = new Object();
   
       private volatile int count;
   
       public Pulse() {
   
           super();
   
           count = 0;
       }
   
       public void pulse() {
   
           synchronized (Lock) {
   
               count++;
   
               Lock.notifyAll();
           }
       }
   
       public void waitForPulse() throws InterruptedException {
   
           synchronized (Lock) {
   
               while (count == 0) {
   
                   Lock.wait();
               }
   
               count--;
           }
       }
   }
   

   and:

   public final class Pulse {
   
       private final Object Lock = new Object();
       private volatile int count;
   
       public Pulse() {
           super();
           count = 0;
       }
   
       public void pulse() {
           synchronized (Lock) {
               count++;
               Lock.notifyAll();
           }
       }
   
       public void waitForPulse() throws InterruptedException {
           synchronized (Lock) {
               while (count == 0) {
                   Lock.wait();
               }
               count--;
           }
       }
   
   }
   

   Note that I've kept some spaces.

3. private final Object Lock = new Object();

   Java conventions state that variable names are camelCase, not PascalCase. Change Lock to lock.