如果未启动，如何仅执行调度程序？

发布于 2025-02-08 13:27:28 字数 255 浏览 1 评论 0原文

ScheduledExecutorService executor = Executors.newScheduledThreadPool(1);
if(executor.isShutdown()) {
    executor.scheduleAtFixedRate(helloRunnable, 0, 1, TimeUnit.SECONDS);
}

每次发生事件时都执行此代码，我该如何仅第一次执行它

？ >但是它不起作用

原文

ScheduledExecutorService executor = Executors.newScheduledThreadPool(1);
if(executor.isShutdown()) {
    executor.scheduleAtFixedRate(helloRunnable, 0, 1, TimeUnit.SECONDS);
}

This piece of code is executed everytime a event happens, how do i make it only execute for the first time?(like, if the scheduler is starter, do not execute)

I tried using executor.isShutdown() but it does not work

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紫瑟鸿黎 2025-02-15 13:27:28

您可以使用atomicboolean来管理对执行者的访问：

    private final ScheduledExecutorService executor = Executors.newSingleThreadScheduledExecutor();
    private static final AtomicBoolean IS_ACTIVE = new AtomicBoolean(false);

    private void startScheduler() {
        if (IS_ACTIVE.compareAndSet(false, true)) {
            executor.scheduleAtFixedRate(() -> {}, 0L, 5L, TimeUnit.SECONDS);
        }
    }

或者您可以使用同步和懒惰的初始化来使其起作用：

    private volatile ScheduledExecutorService scheduler;

    public void startScheduler() {
        if (scheduler == null) {
            this.initAndStart();
        }
    }

    private synchronized void initAndStart() {
        if (scheduler == null) {
            scheduler = Executors.newSingleThreadScheduledExecutor();
            scheduler.schedule(() -> log.info("Started, Thread: {}", Thread.currentThread().getName()), 0L, TimeUnit.SECONDS);
        }
    }

note note ：它将尝试尝试要阻止设法调用initandstart的当前类和线程也将导致阻塞，但是一旦调度程序初始化

You can use AtomicBoolean to manage access to the executor:

    private final ScheduledExecutorService executor = Executors.newSingleThreadScheduledExecutor();
    private static final AtomicBoolean IS_ACTIVE = new AtomicBoolean(false);

    private void startScheduler() {
        if (IS_ACTIVE.compareAndSet(false, true)) {
            executor.scheduleAtFixedRate(() -> {}, 0L, 5L, TimeUnit.SECONDS);
        }
    }

Or you can use synchronized and lazy initialization to make it work:

    private volatile ScheduledExecutorService scheduler;

    public void startScheduler() {
        if (scheduler == null) {
            this.initAndStart();
        }
    }

    private synchronized void initAndStart() {
        if (scheduler == null) {
            scheduler = Executors.newSingleThreadScheduledExecutor();
            scheduler.schedule(() -> log.info("Started, Thread: {}", Thread.currentThread().getName()), 0L, TimeUnit.SECONDS);
        }
    }

Note: It will try to block current class and threads which managed to call initAndStart will also cause blocking, but as soon as scheduler is initialized there will be no blocking

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