Java Executors newCachedThreadPool example 2017-08-21 02:40

Executors.newCachedThreadPool() method will create a thread pool which core pool size is 0 and max pool size is Integer.MAX_VALUE. The detail of constructor function is here:

new ThreadPoolExecutor(0, Integer.MAX_VALUE, 60L, TimeUnit.SECONDS, new SynchronousQueue<Runnable>());

This thread pool will always create a thread when there is no thread for new tasks. It uses SynchronousQueue to queue the new tasks, that means new tasks will always be executed. I wrote the sample code to help me understand it.

ThreadInfo for recording the information of thread

public class ThreadInfo {
    private String threadName;
    private String workerName;

    public String getThreadName() {
        return threadName;

    public void setThreadName(String threadName) {
        this.threadName = threadName;

    public String getWorkerName() {
        return workerName;

    public void setWorkerName(String workerName) {
        this.workerName = workerName;


public class Worker implements Callable<ThreadInfo> {
    private String workerName;

    public Worker(String workerName) {
        this.workerName = workerName;

    public ThreadInfo call() throws Exception {
        ThreadInfo threadInfo = new ThreadInfo();
        return threadInfo;


public class NewCachedThreadPoolClient {
    public static void main(String[] args) throws ExecutionException, InterruptedException {
        Set<String> workersName = new HashSet<>();
        Set<String> threadsName = new HashSet<>();
        ExecutorService pool = Executors.newCachedThreadPool();
        List<Future<ThreadInfo>> futureList = new ArrayList<>();
        for (int i = 0; i < 1000; i++) {
            Worker t1 = new Worker("Thread " + i);
            Future<ThreadInfo> future = pool.submit(t1);
        for (Future<ThreadInfo> future : futureList) {
            ThreadInfo threadInfo = future.get();
        System.out.println("workers num:" + workersName.size());
        System.out.println("threads num:" + threadsName.size());

The output in my environment:

workers num:1000
threads num:379

The output means 1000 tasks are submitted, but only 379 threads are created. Thread pool will reuse the alive thread to execute the new task. You can change the Thread.sleep(10) to make the task finish more quickly or slower. The slower task finished the more threads will be created.