英文:
For Java's ScheduledExecutorService's scheduleAtFixedRate method does it return 1 ScheduledFuture or many?
问题
因为有一个可以多次执行的命令，所以我提出了这个问题。它在每次执行命令时是否都会返回一个ScheduledFuture，还是在某个时候会返回一个单独的ScheduledFuture？
英文:
I ask this question because there is a command that executes multiple times. Does it return a ScheduledFuture every time the command executes or does it return a single ScheduledFuture at some point?
答案1
得分: 4
仅在安排“Runnable命令”时返回单个ScheduledFuture<?>。
根据Javadoc，scheduleAtFixedRate 返回
> 一个代表重复任务系列待完成的ScheduledFuture
您还可以在方法签名中看到：
ScheduledFuture<?> scheduleAtFixedRate(Runnable command, long initialDelay, long period, TimeUnit unit)
“Runnable命令”将根据配置的间隔继续执行，无需进一步干预。
> 任务执行的序列持续无限期，直到发生以下异常完成之一：
>
> - 通过返回的future明确取消任务。
> - 执行程序终止，也会导致任务取消。
> - 任务的执行抛出异常。
通过在Future上调用cancel来通过编程方式终止Runnable命令的所有未来计划执行，scheduleAtFixedRate返回单个ScheduledFuture提供了有用的机制。
英文:
Only a single ScheduledFuture<?> is returned upon scheduling the Runnable command.
According to the Javadoc, scheduleAtFixedRate returns
> a ScheduledFuture representing pending completion of the series
> of repeated tasks
You can also see this in the method signature:
ScheduledFuture<?> scheduleAtFixedRate(Runnable command, long initialDelay, long period, TimeUnit unit)
The Runnable command continues to be executed according to the configured interval without further intervention.
> The sequence of task executions continues indefinitely until one of
> the following exceptional completions occur:
>
> - The task is explicitly cancelled via the returned future.
> - The executor terminates, also resulting in task cancellation.
> - An execution of the task throws an exception.
Having a single ScheduledFuture returned by scheduleAtFixedRate provides a useful mechanism to programmatically discontinue all future scheduled executions of Runnable command through a call to cancel on the Future.
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