Add Timer.isCancelled() method

[jimtng]

I found the need for Timer.isCancelled() inside a long running timer that self-reschedules itself.

Example:

var timer = null

rule "Long running timer"
when
    System started
then
    timer = createTimer(now.plusSeconds(1), [|
        downloadFile() // do something that takes a long time here, e.g. a http get from a large source            
        timer.reschedule(now.plusSeconds(1))
    ])
end

rule "Cancel the timer"
when
    Item Switch1 received command ON
then
    timer.cancel()
end

When Switch1 received a command ON while downloadFile() is executing, the timer got cancelled, but the currently running task is still continuing, it will reschedule the timer and therefore the timer continues to run despite having been "cancelled".

In this case, the timer code can check with isCancelled() before calling reschedule as such:

rule "Long running timer"
when
    System started
then
    timer = createTimer(now.plusSeconds(1), [|
        downloadFile() // do something that takes a long time here, e.g. a http get from a large source
        if (!timer.isCancelled())  {
            timer.reschedule(now.plusSeconds(1))
        }
    ])
end

[cweitkamp]

LGTM. Thanks.

[cweitkamp]

Not related to your contribution but I am wondering if we should synchronize this method to have a thread safe implementation? Wdyt?

[jimtng]

It appears to be thread safe already https://docs.oracle.com/en/java/javase/11/docs/api/java.base/java/util/concurrent/CompletableFuture.html#cancel(boolean)

[cweitkamp]

What I am talking about is a small race condition on the future property of this implementation when calling the reschedule(...) method because we first cancel the existing future and afterwards assign a new CompletableFuture to it.