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[ZScheduler] Store pointers to mutable references in stack memory to avoid reading them from the heap #9868

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Merged
merged 1 commit into from
May 20, 2025
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[ZScheduler] Store pointers to mutable references in stack memory to avoid reading them from the heap #9868

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19 changes: 14 additions & 5 deletions core/jvm-native/src/main/scala/zio/internal/ZScheduler.scala
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Original file line number Diff line number Diff line change
Expand Up @@ -29,7 +29,7 @@ import scala.collection.mutable
* applications. Inspired by "Making the Tokio Scheduler 10X Faster" by Carl
* Lerche. [[https://tokio.rs/blog/2019-10-scheduler]]
*/
private final class ZScheduler(autoBlocking: Boolean) extends Executor {
private final class ZScheduler(autoBlocking: Boolean) extends Executor { parent =>

import Trace.{empty => emptyTrace}
import ZScheduler.{poolSize, workerOrNull}
Expand Down Expand Up @@ -266,14 +266,23 @@ private final class ZScheduler(autoBlocking: Boolean) extends Executor {
private[this] def makeWorker(): ZScheduler.Worker =
new ZScheduler.Worker {
self =>
override val submittedLocations = makeLocations()
override val submittedLocations: ZScheduler.Locations = makeLocations()

final override def run(): Unit = {
// Store parent mutable object references in stack memory to avoid fetching it from the heap every time
val globalQueue = parent.globalQueue
val workers = parent.workers
val state = parent.state
val cache = parent.cache
val idle = parent.idle
val poolSize = ZScheduler.poolSize

override def run(): Unit = {
var currentBlocking = false
var currentOpCount = 0L
val random = ThreadLocalRandom.current
var runnable = null.asInstanceOf[Runnable]
var searching = false

while (!isInterrupted) {
currentBlocking = blocking
val currentNextRunnable = nextRunnable
Expand Down Expand Up @@ -321,7 +330,7 @@ private final class ZScheduler(autoBlocking: Boolean) extends Executor {
currentBlocking = blocking
if (currentBlocking) {
val runnables = localQueue.pollUpTo(256)
if (runnables.nonEmpty) {
if (!runnables.isEmpty) {
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Is this because of the interface dispatch? I think we could override it even though it's marked deprecatedOverriding

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@kyri-petrou kyri-petrou May 20, 2025 •
edited
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Is this because of the interface dispatch

Yeap

I think we could override it

I'm a bit worried that it'll make things a bit worse for the rest of the std library collections. My knowledge on the matter is not the best but I think that the more overrides a method has, it makes interface dispatches for that method slower. I could be wrong on that though, I vaguely remember reading that somewhere.

globalQueue.offerAll(runnables, random)
}
}
Expand Down Expand Up @@ -388,7 +397,7 @@ private final class ZScheduler(autoBlocking: Boolean) extends Executor {

// NOTE: Synchronized block in case the supervisor attempts to mark the worker as blocking at the same time
// as an external call
def markAsBlocking(): Unit = synchronized {
final def markAsBlocking(): Unit = synchronized {
if (blocking) ()
else {
blocking = true
Expand Down