如何更改 ScheduledExecutorService 中的线程池大小？

Question

I need ScheduledExecutorService with a dynamic thread pool. I want to change the thread pool size dynamically. How can I do this?

class ExecutorTask {
    private ScheduledExecutorService service;

    public void add(Task task) {
        // I need thread pool size == count added tasks.
        service.scheduleAtFixedRate(this::start, 0, 10, TimeUnit.SECONDS);
    }
}

Maybe you can advice me another thread pool?

Answer 1

You can easily do that with ScheduledThreadPoolExecutor .

    //Init executor
    int initialPoolSize = 5;
    ScheduledThreadPoolExecutor executor = new ScheduledThreadPoolExecutor(initialPoolSize);

    //[...] do something

    //Change max size
    int newPoolSize = 10;
    executor.setCorePoolSize(newPoolSize);

Note that the inherited method setMaximumPoolSize(int) has no effect on ScheduledThreadPoolExecutor . To change the pool size you need to change the corePoolSize:

While this class inherits from ThreadPoolExecutor, a few of the inherited tuning methods are not useful for it. In particular, because it acts as a fixed-sized pool using corePoolSize threads and an unbounded queue, adjustments to maximumPoolSize have no useful effect. Additionally, it is almost never a good idea to set corePoolSize to zero or use allowCoreThreadTimeOut because this may leave the pool without threads to handle tasks once they become eligible to run.

Answer 2

也许这就是您在 Executors Util 类中寻找的内容：

ExecutorService executorService = Executors.newScheduledThreadPool(5)

Answer 3

you can use setCorePoolSize(int) method for that.

Also using Executors.newCachedThreadPool you provide the responsibility of creating the thread pool size to ThreadPoolExecutor .

The ThreadPoolExecutor creates new threads if needed to execute the new tasks, and reuses the existing ones with Executors.newCachedThreadPool()