From 12f1887fd56bbd5eebb82ff3e389a61e73192962 Mon Sep 17 00:00:00 2001
From: kyri-petrou <67301607+kyri-petrou@users.noreply.github.com>
Date: Fri, 16 May 2025 18:17:22 -0600
Subject: [PATCH] [ZScheduler] Store pointers to mutable references in stack
 memory to avoid fetching them from the heap

---
 .../main/scala/zio/internal/ZScheduler.scala  | 19 ++++++++++++++-----
 1 file changed, 14 insertions(+), 5 deletions(-)

diff --git a/core/jvm-native/src/main/scala/zio/internal/ZScheduler.scala b/core/jvm-native/src/main/scala/zio/internal/ZScheduler.scala
index 725ec50e73aa..e6a22715d3f4 100644
--- a/core/jvm-native/src/main/scala/zio/internal/ZScheduler.scala
+++ b/core/jvm-native/src/main/scala/zio/internal/ZScheduler.scala
@@ -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}
@@ -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
@@ -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) {
                             globalQueue.offerAll(runnables, random)
                           }
                         }
@@ -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