package demo;

import java.util.concurrent.ForkJoinPool;
import java.util.concurrent.locks.LockSupport;

public class ForkJoinPoolTest {
	/*
	 * java -version
	 * java version "21.0.8" 2025-07-15 LTS
	 * Java(TM) SE Runtime Environment (build 21.0.8+12-LTS-250)
     * Java HotSpot(TM) 64-Bit Server VM (build 21.0.8+12-LTS-250, mixed mode, sharing)
     */
	public static void main(String[] args) throws InterruptedException {
		//Add a breakpoint on the 1864th line of ForkJoinPool source code in awaitWork method.
		
		ForkJoinPool pool = new ForkJoinPool(2);//total 2 Threads
		
		//create worker w1, keep running and printing pool information
		pool.submit(() -> {
			while(true) {
				System.err.println("===================");
				System.err.println("QueuedSubmissionCount:" + pool.getQueuedSubmissionCount());
				System.err.println("ActiveThreadCount:" + pool.getActiveThreadCount());
				System.err.println("PoolSize:" + pool.getPoolSize());
				System.err.println("===================");
				
				LockSupport.parkNanos(5 * 1000_000_000L);//5s
			}
		});
		
		//create another worker w2
		pool.submit(() -> System.out.println(Thread.currentThread().getName() + " : finished task1"));
		System.out.println("submited task1");
		
		Thread.sleep(3 * 1000);// waiting for task1 to end
		//now task1 finished and no task in queue, w2 is pausing at breakpoint in  awaitWork method.
		
		pool.submit(() -> System.out.println(Thread.currentThread().getName() + " : finished task2"));
		System.out.println("submited task2");
		//after submitted task2, resume w2 , and then w2 will park on line 1891 ,although there is still task2 in the Submission queue 
		
		Thread.sleep(5 * 60 * 1000);
		pool.close();
	}

}