Multithreading — Yield

The static method Thread#yield() causes the current thread to yield its current use of a processor.

In other words the current thread may stop executing momentarily to give chance to other competing threads having the same priorities.

public class ThreadYieldExample {

    public static void main(String[] args) {
        Task task1 = new Task(true);
        new Thread(task1).start();

        Task task2 = new Task(false);
        new Thread(task2).start();
    }

    private static class Task implements Runnable {
        private int counter;
        private final boolean shouldYield;

        private Task(boolean shouldYield) {
            this.shouldYield = shouldYield;
        }

        @Override
        public void run() {
            System.out.println(Thread.currentThread().getName() + " started.");
            for (int i = 0; i < 1000; i++) {
                counter++;
                if(shouldYield){
                    Thread.yield();
                }
            }
            System.out.println(Thread.currentThread().getName() + " ended.");
        }
    }
}

In above example we are yielding the first thread in favor of other. As a result the first thread spends less CPU time and it becomes slower than the other, hence ‘Thread-0 ended.’ printed at the end all the time

Output

Thread-0 started.
Thread-1 started.
Thread-1 ended.
Thread-0 ended.

Just like thread priorities, yield method behavior varies from OS to OS. We shouldn’t make coding decisions based on this method. Also this is only a hint, the thread scheduler (on OS level) is free to ignore this hint.