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Optimize debounce operator allocation pressure by using conflated pro… #1415

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Merged
merged 1 commit into from
Aug 9, 2019
Merged

Optimize debounce operator allocation pressure by using conflated pro… #1415

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8 changes: 8 additions & 0 deletions kotlinx-coroutines-core/common/src/flow/internal/NullSurrogate.kt
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Original file line number Diff line number Diff line change
Expand Up @@ -14,3 +14,11 @@ import kotlin.jvm.*
@JvmField
@SharedImmutable
internal val NULL = Symbol("NULL")

/*
* Symbol used to indicate that the flow is complete.
* It should never leak to the outside world.
*/
@JvmField
@SharedImmutable
internal val DONE = Symbol("DONE")
33 changes: 14 additions & 19 deletions kotlinx-coroutines-core/common/src/flow/operators/Delay.kt
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Expand Up @@ -62,18 +62,21 @@ public fun <T> Flow<T>.delayEach(timeMillis: Long): Flow<T> = flow {
public fun <T> Flow<T>.debounce(timeoutMillis: Long): Flow<T> {
require(timeoutMillis > 0) { "Debounce timeout should be positive" }
return scopedFlow { downstream ->
val values = Channel<Any?>(Channel.CONFLATED) // Actually Any, KT-30796
// Channel is not closed deliberately as there is no close with value
val collector = async {
collect { value -> values.send(value ?: NULL) }
// Actually Any, KT-30796
val values = produce<Any?>(capacity = Channel.CONFLATED) {
collect { value -> send(value ?: NULL) }
}

var isDone = false
var lastValue: Any? = null
while (!isDone) {
while (lastValue !== DONE) {
select<Unit> {
values.onReceive {
lastValue = it
// Should be receiveOrClosed when boxing issues are fixed
values.onReceiveOrNull {
if (it == null) {
if (lastValue != null) downstream.emit(NULL.unbox(lastValue))
lastValue = DONE
} else {
lastValue = it
}
}

lastValue?.let { value ->
Expand All @@ -83,12 +86,6 @@ public fun <T> Flow<T>.debounce(timeoutMillis: Long): Flow<T> {
downstream.emit(NULL.unbox(value))
}
}

// Close with value 'idiom'
collector.onAwait {
if (lastValue != null) downstream.emit(NULL.unbox(lastValue))
isDone = true
}
}
}
}
Expand Down Expand Up @@ -118,16 +115,14 @@ public fun <T> Flow<T>.sample(periodMillis: Long): Flow<T> {
// Actually Any, KT-30796
collect { value -> send(value ?: NULL) }
}

var isDone = false
var lastValue: Any? = null
val ticker = fixedPeriodTicker(periodMillis)
while (!isDone) {
while (lastValue !== DONE) {
select<Unit> {
values.onReceiveOrNull {
if (it == null) {
ticker.cancel(ChildCancelledException())
isDone = true
lastValue = DONE
} else {
lastValue = it
}
Expand Down