Remove trailing references from ManagedArray and Heap

Author: lilleyse

Source/Core/Heap.js

@@ -24,6 +24,16 @@ function Heap(options) {
   this._maximumLength = undefined;
 }
 
+function removeTrailingReferences(heap, newLength) {
+  var originalLength = heap._length;
+  if (newLength < originalLength) {
+    var array = heap._array;
+    for (var i = newLength; i < originalLength; ++i) {
+      array[i] = undefined;
+    }
+  }
+}
+
 Object.defineProperties(Heap.prototype, {
   /**
    * Gets the length of the heap.
@@ -65,6 +75,7 @@ Object.defineProperties(Heap.prototype, {
       return this._maximumLength;
     },
     set: function (value) {
+      removeTrailingReferences(this, value);
       this._maximumLength = value;
       if (this._length > value && value > 0) {
         this._length = value;
@@ -211,6 +222,7 @@ Heap.prototype.pop = function (index) {
   var root = array[index];
   swap(array, index, --this._length);
   this.heapify(index);
+  array[this._length] = undefined; // Remove trailing reference
   return root;
 };
 

Source/Core/ManagedArray.js

@@ -16,6 +16,16 @@ function ManagedArray(length) {
   this._length = length;
 }
 
+function removeTrailingReferences(managedArray, newLength) {
+  var array = managedArray._array;
+  var originalLength = managedArray._length;
+  if (newLength < originalLength) {
+    for (var i = newLength; i < originalLength; ++i) {
+      array[i] = undefined;
+    }
+  }
+}
+
 Object.defineProperties(ManagedArray.prototype, {
   /**
    * Gets or sets the length of the array.
@@ -29,6 +39,7 @@ Object.defineProperties(ManagedArray.prototype, {
       return this._length;
     },
     set: function (length) {
+      removeTrailingReferences(this, length);
       this._length = length;
       if (length > this._array.length) {
         this._array.length = length;
@@ -74,7 +85,7 @@ ManagedArray.prototype.set = function (index, element) {
   Check.typeOf.number("index", index);
   //>>includeEnd('debug');
 
-  if (index >= this.length) {
+  if (index >= this._length) {
     this.length = index + 1;
   }
   this._array[index] = element;
@@ -105,7 +116,12 @@ ManagedArray.prototype.push = function (element) {
  * @returns {*} The last element in the array.
  */
 ManagedArray.prototype.pop = function () {
-  return this._array[--this.length];
+  if (this._length === 0) {
+    return undefined;
+  }
+  var element = this._array[this._length - 1];
+  --this.length;
+  return element;
 };
 
 /**
@@ -142,7 +158,7 @@ ManagedArray.prototype.resize = function (length) {
  * @param {Number} [length] The length.
  */
 ManagedArray.prototype.trim = function (length) {
-  length = defaultValue(length, this.length);
+  length = defaultValue(length, this._length);
   this._array.length = length;
 };
 export default ManagedArray;

Specs/Core/HeapSpec.js

@@ -3,6 +3,15 @@ import { Heap } from "../../Source/Cesium.js";
 describe("Core/Heap", function () {
   var length = 100;
 
+  function expectTrailingReferenceToBeRemoved(heap) {
+    var array = heap._array;
+    var length = heap._length;
+    var reservedLength = array.length;
+    for (var i = length; i < reservedLength; ++i) {
+      expect(array[i]).toBeUndefined();
+    }
+  }
+
   function checkHeap(heap, comparator) {
     var array = heap.internalArray;
     var pass = true;
@@ -90,6 +99,34 @@ describe("Core/Heap", function () {
     expect(pass).toBe(true);
   });
 
+  it("pop removes trailing references", function () {
+    var heap = new Heap({
+      comparator: comparator,
+    });
+
+    for (var i = 0; i < 10; ++i) {
+      heap.insert(Math.random());
+    }
+
+    heap.pop();
+    heap.pop();
+
+    expectTrailingReferenceToBeRemoved(heap);
+  });
+
+  it("setting maximum length less than current length removes trailing references", function () {
+    var heap = new Heap({
+      comparator: comparator,
+    });
+
+    for (var i = 0; i < 10; ++i) {
+      heap.insert(Math.random());
+    }
+
+    heap.maximumLength = 5;
+    expectTrailingReferenceToBeRemoved(heap);
+  });
+
   it("insert returns the removed element when maximumLength is set", function () {
     var heap = new Heap({
       comparator: comparator,

Specs/Core/ManagedArraySpec.js

@@ -1,6 +1,15 @@
 import { ManagedArray } from "../../Source/Cesium.js";
 
 describe("Core/ManagedArray", function () {
+  function expectTrailingReferenceToBeRemoved(managedArray) {
+    var array = managedArray._array;
+    var length = managedArray._length;
+    var reservedLength = array.length;
+    for (var i = length; i < reservedLength; ++i) {
+      expect(array[i]).toBeUndefined();
+    }
+  }
+
   it("constructor has expected default values", function () {
     var array = new ManagedArray();
     expect(array.length).toEqual(0);
@@ -90,6 +99,24 @@ describe("Core/ManagedArray", function () {
     }
   });
 
+  it("pop removes trailing references", function () {
+    var length = 10;
+    var array = new ManagedArray(length);
+    array.set(0, Math.random());
+    array.set(1, Math.random());
+    array.set(2, Math.random());
+    array.pop();
+    array.pop();
+    expectTrailingReferenceToBeRemoved(array);
+  });
+
+  it("pop returns undefined if array is empty", function () {
+    var array = new ManagedArray();
+    array.push(1);
+    expect(array.pop()).toBe(1);
+    expect(array.pop()).toBeUndefined();
+  });
+
   it("reserve throws if length is less than 0", function () {
     var array = new ManagedArray();
     expect(function () {
@@ -130,6 +157,16 @@ describe("Core/ManagedArray", function () {
     expect(array.length).toEqual(5);
   });
 
+  it("resize removes trailing references", function () {
+    var length = 10;
+    var array = new ManagedArray(length);
+    array.set(0, Math.random());
+    array.set(1, Math.random());
+    array.set(2, Math.random());
+    array.resize(1);
+    expectTrailingReferenceToBeRemoved(array);
+  });
+
   it("trim", function () {
     var array = new ManagedArray(2);
     array.reserve(10);