SingleThreadPool

package multithreading.thread_pool.types;

import java.util.HashSet;
import java.util.Set;
import java.util.concurrent.*;

public class ScheduledThreadPoolClient {

    private static final int TASKS_COUNT = 10_000;
    private static final Set<String> threadNames = new HashSet<>();
    public static void main(String[] args) throws InterruptedException {
        ExecutorService service = Executors.newSingleThreadExecutor();

        for (int i = 0; i < TASKS_COUNT; i++) {
            int finalI = i;
            Runnable task = () -> {
                System.out.println("Thread " + Thread.currentThread().getName() + " executes " + finalI + " task");
                synchronized (threadNames) {
                    threadNames.add(Thread.currentThread().getName());
                }
            };
            service.submit(task);
        }

        service.shutdown();
        service.awaitTermination(30, TimeUnit.SECONDS);
        System.out.println("Count of used threads " + threadNames.size());
    }
}