如果再次调用相同的函数，则取消 kotlin 中的挂起函数

Question

I want to cancel the function i created which simply increments a counter value. For example, if the specific function is triggered by click, I only want to display the log for the last uninterrupted click within 2 seconds. Basically, i want the function to cancel itself if called again if its ongoing (delay is ongoing). Is there such thing in kotlin?

val counter = mutableStateOf(0)
suspend fun addCounter(){
    counter.value++
    
   
    delay(2000)
    Log.e("click cat","click $counter")
}`

Answer 1

This kind of event processing is usually handled using reactive streams and is often named the debounce operator. It exists in both ReactiveX ( Debounce ) and in Kotlin flows ( debounce() ).

As you already use coroutines, I suggest going with Kotlin flows. Please see the example below:

private val flow = MutableStateFlow(0)

suspend fun main() = coroutineScope {
    launch {
        // consumer of events
        flow
            .debounce(2.seconds)
            .collect { println(it) }
    }

    // producer
    delay(100)
    addCounter() // 1
    delay(500)
    addCounter() // 2, ignore 1
    delay(500)
    addCounter() // 3, ignore 2
    delay(2500) // show 3
    addCounter() // 4
    delay(500)
    addCounter() // 5, ignore 4
    delay(3000) // show 5
}

fun addCounter() {
    flow.value++
}

It shows only 3 and 5 , because all other events were "cancelled" by subsequent events that came too fast.

Answer 2

Suspend function is a function that could be started, paused, and resume. Suspend functions are only allowed to be called from a coroutine or another suspend function and you can not cancel it in this way. Coroutine structured concurrency is the thing that you're looking for. You can use a Job to perform your task above. Now you can cancel the job anytime you need.