Added new ProcessQueue struct for classes that need this pattern a lot

v3/src/structs/ProcessQueue.js

@@ -0,0 +1,99 @@
+//  Phaser.Structs.ProcessQueue
+
+var Class = require('../utils/Class');
+
+var ProcessQueue = new Class({
+
+    initialize:
+
+    function ProcessQueue ()
+    {
+        this._pending = [];
+        this._active = [];
+        this._destroy = [];
+
+        this._toProcess = 0;
+    },
+
+    add: function (item)
+    {
+        this._pending.push(item);
+
+        this._toProcess++;
+
+        return this;
+    },
+
+    remove: function (item)
+    {
+        this._destroy.push(item);
+
+        this._toProcess++;
+
+        return this;
+    },
+
+    update: function ()
+    {
+        if (this._toProcess === 0)
+        {
+            //  Quick bail
+            return this._active;
+        }
+
+        var list = this._destroy;
+        var active = this._active;
+        var i;
+        var item;
+
+        //  Clear the 'destroy' list
+        for (i = 0; i < list.length; i++)
+        {
+            item = list[i];
+
+            //  Remove from the 'active' array
+            var idx = active.indexOf(item);
+
+            if (idx !== -1)
+            {
+                active.splice(idx, 1);
+            }
+        }
+
+        list.length = 0;
+
+        //  Process the pending addition list
+        //  This stops callbacks and out of sync events from populating the active array mid-way during an update
+
+        list = this._pending;
+
+        for (i = 0; i < list.length; i++)
+        {
+            item = list[i];
+
+            this._active.push(item);
+        }
+
+        list.length = 0;
+
+        this._toProcess = 0;
+
+        //  The owner of this queue can now safely do whatever it needs to with the active list
+        return this._active;
+    },
+
+    getActive: function ()
+    {
+        return this._active;
+    },
+
+    destroy: function ()
+    {
+        this._pending = [];
+        this._active = [];
+        this._destroy = [];
+    }
+
+});
+
+module.exports = ProcessQueue;

v3/src/structs/index.js

@@ -2,7 +2,9 @@
 
 module.exports = {
 
+    List: require('./List'),
     Map: require('./Map'),
+    ProcessQueue: require('./ProcessQueue'),
     RTree: require('./RTree'),
     Set: require('./Set')