Collapse promise state value; combine with length field.

This reduces memory usage, and also ensures the type of all the handlers is consistently `Function`.
cscott · Dec 8, 2015 · dd0c7e4 · dd0c7e4
1 parent eb1f4ea
commit dd0c7e4
Showing 1 changed file with 21 additions and 18 deletions.
diff --git a/lib/promise.js b/lib/promise.js
@@ -159,11 +159,11 @@ var enqueue = useAsap ? require('asap/raw') : IsCallable(global.setImmediate) ?
      function(task) { setTimeout(task, 0); }); // Fallback
 
 // Constants for Promise implementation
-var PROMISE_IDENTITY = 1;
-var PROMISE_THROWER = 2;
-var PROMISE_PENDING = 3;
-var PROMISE_FULFILLED = 4;
-var PROMISE_REJECTED = 5;
+var PROMISE_IDENTITY = (function(v) { return v; });
+var PROMISE_THROWER = (function(t) { throw t; });
+var PROMISE_PENDING = 0;
+var PROMISE_FULFILLED = 1;
+var PROMISE_REJECTED = 2;
 
 var promiseReactionJob = function(reaction, argument) {
   var promiseCapability = reaction.capabilities;
@@ -196,33 +196,35 @@ var triggerPromiseReactions = function(reactions, argument) {
 };
 
 var fulfillPromise = function(promise, value) {
+  /* jshint bitwise: false */
   var reactions = [];
-  if (promise._promise_length > 0) {
+  var length = promise._promise_state >>> 2;
+  if (length > 0) {
     reactions.push(promise._promise_fulfillReactions0);
-    for (var i = 1; i < promise._promise_length; i++) {
+    for (var i = 1; i < length; i++) {
       reactions.push(promise[2 * (i - 1)]);
     }
   }
   promise._promise_result = value;
   promise._promise_fulfillReactions0 = void 0;
   promise._promise_rejectReactions0 = void 0;
-  promise._promise_length = 0;
   promise._promise_state = PROMISE_FULFILLED;
   triggerPromiseReactions(reactions, value);
 };
 
 var rejectPromise = function(promise, reason) {
+  /* jshint bitwise: false */
   var reactions = [];
-  if (promise._promise_length > 0) {
+  var length = promise._promise_state >>> 2;
+  if (length > 0) {
     reactions.push(promise._promise_rejectReactions0);
-    for (var i = 1; i < promise._promise_length; i++) {
+    for (var i = 1; i < length; i++) {
       reactions.push(promise[1 + 2 * (i - 1)]);
     }
   }
   promise._promise_result = reason;
   promise._promise_fulfillReactions0 = void 0;
   promise._promise_rejectReactions0 = void 0;
-  promise._promise_length = 0;
   promise._promise_state = PROMISE_REJECTED;
   triggerPromiseReactions(reactions, reason);
 };
@@ -272,7 +274,7 @@ var Promise = function Promise(resolver) {
   if (!(this instanceof Promise)) {
     throw new TypeError('Constructor Promise requires "new"');
   }
-  if (this && this._promise_state) {
+  if (this && typeof this._promise_state !== 'undefined') {
     throw new TypeError('Bad construction');
   }
   // see https://bugs.ecmascript.org/show_bug.cgi?id=2482
@@ -286,7 +288,6 @@ var Promise = function Promise(resolver) {
   // on the object's element array to avoid unnecessary indirection.
   this._promise_result = void 0;
   this._promise_state = PROMISE_PENDING;
-  this._promise_length = 0;
   this._promise_fulfillReactions0 = void 0;
   this._promise_rejectReactions0 = void 0;
   var resolvingFunctions = createResolvingFunctions(this);
@@ -333,6 +334,7 @@ defineProperties(Promise$prototype, {
   },
 
   then: function then(onFulfilled, onRejected) {
+    /* jshint bitwise: false */
     var promise = this;
     if (!IsPromise(promise)) { throw new TypeError('not a promise'); }
     var C = SpeciesConstructor(promise, Promise);
@@ -352,18 +354,19 @@ defineProperties(Promise$prototype, {
       capabilities: resultCapability,
       handler: onRejected,
     };
-    var value;
-    switch (promise._promise_state) {
+    var value, length;
+    switch (promise._promise_state & 3) {
     case PROMISE_PENDING:
-      if (promise._promise_length === 0) {
+      length = promise._promise_state >>> 2;
+      if (length === 0) {
         promise._promise_fulfillReactions0 = fulfillReaction;
         promise._promise_rejectReactions0 = rejectReaction;
       } else {
-        var i = 2 * (promise._promise_length - 1);
+        var i = 2 * (length - 1);
         promise[i] = fulfillReaction;
         promise[i + 1] = rejectReaction;
       }
-      promise._promise_length++;
+      promise._promise_state += (1 << 2);
       break;
     case PROMISE_FULFILLED:
       value = promise._promise_result;