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?

• SirPython: Welcome to Code Review! What do you mean by, "Will my code work as expected?" Have you not tested your code?
• sdgfsdh: Well it works in my simple tests, but I don't know if I have applied the concurrency primitives correctly.

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.