timers: use only a single TimerWrap instance

Hang all timer lists off a single TimerWrap and use the PriorityQueue
to manage expiration priorities. This makes the Timers code clearer,
consumes significantly less resources and improves performance.

PR-URL: #20555
Fixes: #16105
Reviewed-By: Ben Noordhuis <info@bnoordhuis.nl>
Reviewed-By: Jeremiah Senkpiel <fishrock123@rocketmail.com>
Reviewed-By: Matteo Collina <matteo.collina@gmail.com>
Reviewed-By: James M Snell <jasnell@gmail.com>
Reviewed-By: Ruben Bridgewater <ruben@bridgewater.de>

benchmark/timers/timers-cancel-unpooled.js

@@ -4,18 +4,26 @@ const assert = require('assert');
 
 const bench = common.createBenchmark(main, {
   n: [1e6],
+  direction: ['start', 'end']
 });
 
-function main({ n }) {
+function main({ n, direction }) {
 
   const timersList = [];
   for (var i = 0; i < n; i++) {
     timersList.push(setTimeout(cb, i + 1));
   }
 
+  var j;
   bench.start();
-  for (var j = 0; j < n + 1; j++) {
-    clearTimeout(timersList[j]);
+  if (direction === 'start') {
+    for (j = 0; j < n; j++) {
+      clearTimeout(timersList[j]);
+    }
+  } else {
+    for (j = n - 1; j >= 0; j--) {
+      clearTimeout(timersList[j]);
+    }
   }
   bench.end(n);
 }

benchmark/timers/timers-insert-unpooled.js

@@ -4,18 +4,26 @@ const assert = require('assert');
 
 const bench = common.createBenchmark(main, {
   n: [1e6],
+  direction: ['start', 'end']
 });
 
-function main({ n }) {
+function main({ direction, n }) {
   const timersList = [];
 
+  var i;
   bench.start();
-  for (var i = 0; i < n; i++) {
-    timersList.push(setTimeout(cb, i + 1));
+  if (direction === 'start') {
+    for (i = 1; i <= n; i++) {
+      timersList.push(setTimeout(cb, i));
+    }
+  } else {
+    for (i = n; i > 0; i--) {
+      timersList.push(setTimeout(cb, i));
+    }
   }
   bench.end(n);
 
-  for (var j = 0; j < n + 1; j++) {
+  for (var j = 0; j < n; j++) {
     clearTimeout(timersList[j]);
   }
 }

lib/internal/timers.js

@@ -19,14 +19,15 @@ const {
 // Timeout values > TIMEOUT_MAX are set to 1.
 const TIMEOUT_MAX = 2 ** 31 - 1;
 
-const unrefedSymbol = Symbol('unrefed');
+const kRefed = Symbol('refed');
 
 module.exports = {
   TIMEOUT_MAX,
   kTimeout: Symbol('timeout'), // For hiding Timeouts on other internals.
   async_id_symbol,
   trigger_async_id_symbol,
   Timeout,
+  kRefed,
   initAsyncResource,
   setUnrefTimeout,
   validateTimerDuration
@@ -50,7 +51,7 @@ function initAsyncResource(resource, type) {
 
 // Timer constructor function.
 // The entire prototype is defined in lib/timers.js
-function Timeout(callback, after, args, isRepeat, isUnrefed) {
+function Timeout(callback, after, args, isRepeat) {
   after *= 1; // coalesce to number or NaN
   if (!(after >= 1 && after <= TIMEOUT_MAX)) {
     if (after > TIMEOUT_MAX) {
@@ -62,7 +63,6 @@ function Timeout(callback, after, args, isRepeat, isUnrefed) {
     after = 1; // schedule on next tick, follows browser behavior
   }
 
-  this._called = false;
   this._idleTimeout = after;
   this._idlePrev = this;
   this._idleNext = this;
@@ -75,22 +75,16 @@ function Timeout(callback, after, args, isRepeat, isUnrefed) {
   this._repeat = isRepeat ? after : null;
   this._destroyed = false;
 
-  this[unrefedSymbol] = isUnrefed;
+  this[kRefed] = null;
 
   initAsyncResource(this, 'Timeout');
 }
 
 Timeout.prototype.refresh = function() {
-  if (this._handle) {
-    // Would be more ideal with uv_timer_again(), however that API does not
-    // cause libuv's sorted timers data structure (a binary heap at the time
-    // of writing) to re-sort itself. This causes ordering inconsistencies.
-    this._handle.start(this._idleTimeout);
-  } else if (this[unrefedSymbol]) {
-    getTimers()._unrefActive(this);
-  } else {
+  if (this[kRefed])
     getTimers().active(this);
-  }
+  else
+    getTimers()._unrefActive(this);
 
   return this;
 };
@@ -122,7 +116,7 @@ function setUnrefTimeout(callback, after, arg1, arg2, arg3) {
       break;
   }
 
-  const timer = new Timeout(callback, after, args, false, true);
+  const timer = new Timeout(callback, after, args, false);
   getTimers()._unrefActive(timer);
 
   return timer;