Prevent rule from triggering twice

[rlkoshak (Rich Koshak)]

[No longer relevant on OH 3.0+] Design Pattern: Rule Latching

Edit: Updates for OH 4. Please see Design Pattern: What is a Design Pattern and How Do I Use Them for details on how to work with DPs. Problem Statement Sometimes one wants to make sure that only one instance of a Rule is running at a given time. For example, when a rule is triggered by a Group Item’s receiving updates, the Rule gets triggered more than once per event. Another use is if one needs to implement debouncing where events that take place within a certain time are ignored. No more t…

This is also called “debounce” and if you search the forum for that you will find lots of other posts.

There are a ton of ways to implement it besides ReentrantLocks. For your use case I would probably recommend just using a timestamp.

var lastRing = now

rule "Doorbell"
when
    Item Doorbell received command
then
    if(lastRing.isBefore(now.minusSeconds(30)) {
        // make the doorbell sound/alert
        lastRing = now
    }
end

This way doesn’t depend on finiky locks nor does it require persistence which lastUpdate would require.