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[Performance] Use ArrayDeque for remaining LinkedList queues #516

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[Performance] Use ArrayDeque for remaining LinkedList queues #516

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5fcce7a
[Performance] Use ArrayDeque for remaining LinkedList queues.
Jawnnypoo Jun 15, 2026
7dcc6ad
Size ArrayDeques and reclaim backing array after spikes.
Jawnnypoo Jun 16, 2026
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5 changes: 2 additions & 3 deletions formula/src/main/java/com/instacart/formula/FormulaRuntime.kt
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Original file line number Diff line number Diff line change
Expand Up @@ -11,7 +11,6 @@ import kotlinx.coroutines.CoroutineScope
import kotlinx.coroutines.Job
import kotlinx.coroutines.SupervisorJob
import kotlinx.coroutines.cancel
import java.util.LinkedList
import java.util.concurrent.atomic.AtomicBoolean
import java.util.concurrent.atomic.AtomicReference
import kotlin.coroutines.CoroutineContext
Expand Down Expand Up @@ -82,7 +81,7 @@ class FormulaRuntime<Input : Any, Output : Any>(
/**
* Global transition effect queue which executes side-effects after all formulas are idle.
*/
private val globalEffectQueue = LinkedList<Effect>()
private val globalEffectQueue = ArrayDeque<Effect>()

/**
* Determines if we are iterating through [globalEffectQueue]. It prevents us from
Expand Down Expand Up @@ -342,7 +341,7 @@ class FormulaRuntime<Input : Any, Output : Any>(
private fun executeTransitionEffects() {
isExecutingEffects = true
while (globalEffectQueue.isNotEmpty()) {
val effect = globalEffectQueue.pollFirst()
val effect = globalEffectQueue.removeFirst()
val dispatcher = when (effect.type) {
Effect.Unconfined -> Dispatcher.None
Effect.Main -> Dispatcher.Main
Expand Down
5 changes: 2 additions & 3 deletions formula/src/main/java/com/instacart/formula/batch/BatchImpl.kt
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@@ -1,6 +1,5 @@
package com.instacart.formula.batch

import java.util.LinkedList
import java.util.concurrent.atomic.AtomicBoolean

internal class BatchImpl internal constructor(
Expand All @@ -10,10 +9,10 @@ internal class BatchImpl internal constructor(
) : BatchScheduler.Batch {

private val isScheduled = AtomicBoolean(false)
private val updates = LinkedList<() -> Unit>()
private val updates = ArrayDeque<() -> Unit>()

@Laimiux Laimiux Jun 16, 2026

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Some things to consider with ArrayDeque

  • What is the initial memory allocation? Is that right for our use case?
  • I'm not sure if ArrayDeque sizes down. How likely is it that it spikes in items for a brief moment and then stays there long-term.

@Jawnnypoo Jawnnypoo Jun 16, 2026

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Good callout. It sounds as though the initial memory size would be quite small, less than 100 bytes. As for growing infinitely, that is in fact a problem that this would introduce, though I think even in the thousands, it would be maybe a few kilobytes of memory usage.

We can size down manually. Let me look into that.


fun add(update: () -> Unit) {
updates.add(update)
updates.addLast(update)
}

override fun execute() {
Expand Down
7 changes: 3 additions & 4 deletions formula/src/main/java/com/instacart/formula/runtime/FormulaManagerImpl.kt
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Expand Up @@ -16,7 +16,6 @@ import com.instacart.formula.lifecycle.LifecycleScheduler
import com.instacart.formula.lifecycle.ValidationException
import com.instacart.formula.plugin.ChildAlreadyUsedException
import com.instacart.formula.plugin.FormulaError
import java.util.LinkedList

/**
* Responsible for keeping track of formula's state, running actions, and child formulas. The
Expand Down Expand Up @@ -69,7 +68,7 @@ internal class FormulaManagerImpl<Input, State, Output>(
* while [isRunning] is true. If [isRunning] is false, we will pass the transitions
* to [ManagerDelegate].
*/
private val transitionQueue = LinkedList<DeferredTransition<*, *, *>>()
private val transitionQueue = ArrayDeque<DeferredTransition<*, *, *>>()

fun canUpdatesContinue(evaluationId: Long): Boolean {
return !isEvaluationNeeded(evaluationId) && transitionQueue.isEmpty()
Expand Down Expand Up @@ -307,7 +306,7 @@ internal class FormulaManagerImpl<Input, State, Output>(

// Execute deferred transitions
while (transitionQueue.isNotEmpty()) {
transitionQueue.pollFirst().execute()
transitionQueue.removeFirst().execute()
}

inspector?.onFormulaFinished(formulaType)
Expand Down Expand Up @@ -381,7 +380,7 @@ internal class FormulaManagerImpl<Input, State, Output>(
*/
private fun handleTransitionQueue(evaluationId: Long): Boolean {
while (transitionQueue.isNotEmpty()) {
val event = transitionQueue.pollFirst()
val event = transitionQueue.removeFirst()
event.execute()
if (isEvaluationNeeded(evaluationId)) {
return true
Expand Down
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