import java.util.ArrayList;
import java.util.List;

/**
 * Allocates a large number of a trivial fixed-shape object and a trivial
 * array, then sleeps so `jcmd <pid> GC.class_histogram` can be run against
 * it from outside the container. Used to measure the per-instance byte cost
 * that -XX:+/-UseCompactObjectHeaders actually makes, rather than quoting
 * the JEP's own number. See
 * https://ankurm.com/jvm-flags-for-spring-boot-in-containers-jdk-25-27/
 */
public class HeaderSizeDemo {
    static final class Pair { int a; int b; Pair(int a, int b) { this.a = a; this.b = b; } }

    public static void main(String[] args) throws Exception {
        int count = args.length > 0 ? Integer.parseInt(args[0]) : 2_000_000;
        List<Pair> pairs = new ArrayList<>(count);
        for (int i = 0; i < count; i++) {
            pairs.add(new Pair(i, i));
        }
        System.out.println("allocated " + pairs.size() + " Pair instances, pid=" + ProcessHandle.current().pid());
        System.gc();
        Thread.sleep(120_000);
        System.out.println(pairs.size());
    }
}