From 348287825cdefecdd6dda6ce5c8652fdfc69837c Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Bartek=20Iwa=C5=84czuk?= <biwanczuk@gmail.com>
Date: Wed, 14 Jun 2023 17:04:49 +0200
Subject: [PATCH] perf(web): optimize timer resolution (#19493)

Closes https://github.com/denoland/deno/issues/19348

This changes benchmark from the issue from:
```
deno run -A https://raw.githubusercontent.com/nats-io/nats.deno/deno-transport-changes/examples/bench.js --subject a --payload 3500 --pub --count 650000
pub 7,636 msgs/sec - [85.13 secs] ~ 25.49 MB/sec 85127.8765/85127.8765
```
to:
```
> ./target/release/deno run -A https://raw.githubusercontent.com/nats-io/nats.deno/deno-transport-changes/examples/bench.js --subject a --payload 3500 --pub --count 650000
pub 176,840 msgs/sec - [3.68 secs] ~ 590.27 MB/sec 3675.646833/3675.646833

> ./target/release/deno run -A https://raw.githubusercontent.com/nats-io/nats.deno/deno-transport-changes/examples/bench.js --subject a --payload 3500 --pub --count 650000
pub 174,589 msgs/sec - [3.72 secs] ~ 582.76 MB/sec 3723.01925/3723.01925
```
---
 ext/web/02_timers.js | 33 ++++++++++++++++-----------------
 1 file changed, 16 insertions(+), 17 deletions(-)

diff --git a/ext/web/02_timers.js b/ext/web/02_timers.js
index 27e2e953db..cfabdeb98b 100644
--- a/ext/web/02_timers.js
+++ b/ext/web/02_timers.js
@@ -15,7 +15,6 @@ const {
   MapPrototypeSet,
   Uint8Array,
   Uint32Array,
-  NumberPOSITIVE_INFINITY,
   PromisePrototypeThen,
   SafeArrayIterator,
   SafeMap,
@@ -190,7 +189,7 @@ function initializeTimer(
   // 13. Run steps after a timeout given global, "setTimeout/setInterval",
   // timeout, completionStep, and id.
   runAfterTimeout(
-    () => ArrayPrototypePush(timerTasks, task),
+    task,
     timeout,
     timerInfo,
   );
@@ -203,7 +202,7 @@ function initializeTimer(
 /**
  * @typedef ScheduledTimer
  * @property {number} millis
- * @property {() => void} cb
+ * @property { {action: () => void, nestingLevel: number}[] } task
  * @property {boolean} resolved
  * @property {ScheduledTimer | null} prev
  * @property {ScheduledTimer | null} next
@@ -216,12 +215,12 @@ function initializeTimer(
 const scheduledTimers = { head: null, tail: null };
 
 /**
- * @param {() => void} cb Will be run after the timeout, if it hasn't been
- * cancelled.
+ * @param { {action: () => void, nestingLevel: number}[] } task Will be run
+ * after the timeout, if it hasn't been cancelled.
  * @param {number} millis
  * @param {{ cancelRid: number, isRef: boolean, promiseId: number }} timerInfo
  */
-function runAfterTimeout(cb, millis, timerInfo) {
+function runAfterTimeout(task, millis, timerInfo) {
   const cancelRid = timerInfo.cancelRid;
   let sleepPromise;
   // If this timeout is scheduled for 0ms it means we want it to run at the
@@ -241,7 +240,6 @@ function runAfterTimeout(cb, millis, timerInfo) {
   /** @type {ScheduledTimer} */
   const timerObject = {
     millis,
-    cb,
     resolved: false,
     prev: scheduledTimers.tail,
     next: null,
@@ -260,6 +258,10 @@ function runAfterTimeout(cb, millis, timerInfo) {
   PromisePrototypeThen(
     sleepPromise,
     (cancelled) => {
+      if (timerObject.resolved) {
+        return;
+      }
+
       // "op_void_async_deferred" returns null
       if (cancelled !== null && !cancelled) {
         // The timer was cancelled.
@@ -280,18 +282,15 @@ function runAfterTimeout(cb, millis, timerInfo) {
       //   b) its timeout is lower than the lowest unresolved timeout found so
       //      far in the list.
 
-      timerObject.resolved = true;
-
-      let lowestUnresolvedTimeout = NumberPOSITIVE_INFINITY;
-
       let currentEntry = scheduledTimers.head;
       while (currentEntry !== null) {
-        if (currentEntry.millis < lowestUnresolvedTimeout) {
-          if (currentEntry.resolved) {
-            currentEntry.cb();
-            removeFromScheduledTimers(currentEntry);
-          } else {
-            lowestUnresolvedTimeout = currentEntry.millis;
+        if (currentEntry.millis <= timerObject.millis) {
+          currentEntry.resolved = true;
+          ArrayPrototypePush(timerTasks, task);
+          removeFromScheduledTimers(currentEntry);
+
+          if (currentEntry === timerObject) {
+            break;
           }
         }