Java code to illustrate the regression in Runtime.availableProcessors function

availableProcessorsBug.java

import java.util.concurrent.atomic.AtomicBoolean;
import java.util.concurrent.atomic.AtomicInteger;

public class Main {
    public static void main(String[] args) throws Exception {
        AtomicBoolean stop = new AtomicBoolean();
        AtomicInteger count = new AtomicInteger();

        int numThreads = 1;
        String numThreadsEnv = System.getenv("NUM_THREADS");
        if (numThreadsEnv != null) {
            numThreads = Integer.parseInt(numThreadsEnv);
        }
        System.out.println("Num of Threads = "+ numThreads);

        for (int i = 0; i < numThreads; i++) {
            new Thread(() -> {
                while (!stop.get()) {
                    Runtime.getRuntime().availableProcessors();
                    count.incrementAndGet();
                }
            }).start();
        }

        try {
            int lastCount = 0;
            while (true) {
                Thread.sleep(1000);
                int thisCount = count.get();
                System.out.printf("%s calls/sec %n", thisCount - lastCount);
                lastCount = thisCount;
            }
        }
        finally {
            stop.set(true);
        }
    }
}