When to shutdown Fixed Thread Pool executer in Java?

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I have a JSP application in which a webpage calls five methods one by one (all of them fetch data from different sources) and display charts based on data.
To load the webpage fastly, I planned to call all the five methods in parallel with the help of FixedThreadPool Executor.
Should I shut down my executor once I get the result from all five methods? Shutting down the executor is a bad idea according to me, since if someone opens the webpage a second time it will require the executor to initialize again in order to call the five methods parallelly.
However, I'm not sure about the consequences of leaving the executor open so not sure how to proceed.

thread-safety concurrency threadpool multithreading java
2 Answers

Leaving it open is the normal way to use a thread pool. That's the whole point of thread pools: It's to prevent your application from having to create and then destroy however many new threads every time it needs to load a page. Instead, it can just use the same threads again and again.

user_8018940

In chapter 7 of "Java Concurrency in Practice" there is an example just like this, where a so called one-shot execution service is proposed:

If a method needs to process a batch of tasks and does not return until all the tasks are finished, it can simplify service lifecycle management by using a private Executor whose lifetime is bounded by that method.

Its code example:

boolean checkMail(Set<String> hosts, long timeout, TimeUnit unit)
    throws InterruptedException {
    ExecutorService exec = Executors.newCachedThreadPool();
    final AtomicBoolean hasNewMail = new AtomicBoolean(false);
    try {
        for (final String host : hosts)
            exec.execute(new Runnable() {
                public void run() {
                    if (checkMail(host))
                        hasNewMail.set(true);
                }
    });
    } finally {
        exec.shutdown();
        exec.awaitTermination(timeout, unit);
    }
    return hasNewMail.get();
}

I'd suggest simplifying your code using this approach.

user_37686490
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