From cfb78bc1dfbac335e436eb6c3569535b9f4ebab6 Mon Sep 17 00:00:00 2001
From: Mathias Buus <mathiasbuus@gmail.com>
Date: Tue, 6 Feb 2018 14:58:10 +0100
Subject: [PATCH] process: use linked reusable queue for ticks

PR-URL: https://github.com/nodejs/node/pull/18617
Reviewed-By: Anna Henningsen <anna@addaleax.net>
Reviewed-By: Benjamin Gruenbaum <benjamingr@gmail.com>
Reviewed-By: Ruben Bridgewater <ruben@bridgewater.de>
Reviewed-By: Anatoli Papirovski <apapirovski@mac.com>
Reviewed-By: Benedikt Meurer <benedikt.meurer@gmail.com>
Reviewed-By: Matteo Collina <matteo.collina@gmail.com>
Reviewed-By: Luigi Pinca <luigipinca@gmail.com>
Reviewed-By: Tiancheng "Timothy" Gu <timothygu99@gmail.com>
---
 lib/internal/process/next_tick.js | 76 ++++++++++++++++++++-----------
 1 file changed, 49 insertions(+), 27 deletions(-)

diff --git a/lib/internal/process/next_tick.js b/lib/internal/process/next_tick.js
index e7fad84397c427..84a7402117c5c2 100644
--- a/lib/internal/process/next_tick.js
+++ b/lib/internal/process/next_tick.js
@@ -32,32 +32,55 @@ function setupNextTick() {
   const kHasScheduled = 0;
   const kHasPromiseRejections = 1;
 
-  const nextTickQueue = {
-    head: null,
-    tail: null,
+  // Queue size for each tick array. Must be a factor of two.
+  const kQueueSize = 2048;
+  const kQueueMask = kQueueSize - 1;
+
+  class FixedQueue {
+    constructor() {
+      this.bottom = 0;
+      this.top = 0;
+      this.list = new Array(kQueueSize);
+      this.next = null;
+    }
+
     push(data) {
-      const entry = { data, next: null };
-      if (this.tail !== null) {
-        this.tail.next = entry;
-      } else {
-        this.head = entry;
-        tickInfo[kHasScheduled] = 1;
-      }
-      this.tail = entry;
-    },
+      this.list[this.top] = data;
+      this.top = (this.top + 1) & kQueueMask;
+    }
+
     shift() {
-      if (this.head === null)
-        return;
-      const ret = this.head.data;
-      if (this.head === this.tail) {
-        this.head = this.tail = null;
+      const next = this.list[this.bottom];
+      if (next === undefined) return null;
+      this.list[this.bottom] = undefined;
+      this.bottom = (this.bottom + 1) & kQueueMask;
+      return next;
+    }
+  }
+
+  var head = new FixedQueue();
+  var tail = head;
+
+  function push(data) {
+    if (head.bottom === head.top) {
+      if (head.list[head.top] !== undefined)
+        head = head.next = new FixedQueue();
+      else
+        tickInfo[kHasScheduled] = 1;
+    }
+    head.push(data);
+  }
+
+  function shift() {
+    const next = tail.shift();
+    if (tail.top === tail.bottom) {
+      if (tail.next)
+        tail = tail.next;
+      else
         tickInfo[kHasScheduled] = 0;
-      } else {
-        this.head = this.head.next;
-      }
-      return ret;
     }
-  };
+    return next;
+  }
 
   process.nextTick = nextTick;
   // Needs to be accessible from beyond this scope.
@@ -69,7 +92,7 @@ function setupNextTick() {
   function _tickCallback() {
     let tock;
     do {
-      while (tock = nextTickQueue.shift()) {
+      while (tock = shift()) {
         const asyncId = tock[async_id_symbol];
         emitBefore(asyncId, tock[trigger_async_id_symbol]);
         // emitDestroy() places the async_id_symbol into an asynchronous queue
@@ -93,7 +116,7 @@ function setupNextTick() {
         emitAfter(asyncId);
       }
       runMicrotasks();
-    } while (nextTickQueue.head !== null || emitPromiseRejectionWarnings());
+    } while (head.top !== head.bottom || emitPromiseRejectionWarnings());
     tickInfo[kHasPromiseRejections] = 0;
   }
 
@@ -139,8 +162,7 @@ function setupNextTick() {
           args[i - 1] = arguments[i];
     }
 
-    nextTickQueue.push(new TickObject(callback, args,
-                                      getDefaultTriggerAsyncId()));
+    push(new TickObject(callback, args, getDefaultTriggerAsyncId()));
   }
 
   // `internalNextTick()` will not enqueue any callback when the process is
@@ -168,6 +190,6 @@ function setupNextTick() {
 
     if (triggerAsyncId === null)
       triggerAsyncId = getDefaultTriggerAsyncId();
-    nextTickQueue.push(new TickObject(callback, args, triggerAsyncId));
+    push(new TickObject(callback, args, triggerAsyncId));
   }
 }