Merge pull request #3895 from planetlabs/greedy-multi-queue

Rework the tile queue for multiple queues.

src/ol/tilequeue.js

@@ -89,14 +89,17 @@ ol.TileQueue.prototype.handleTileChange = function(event) {
  * @param {number} maxNewLoads Maximum number of new tiles to load.
  */
 ol.TileQueue.prototype.loadMoreTiles = function(maxTotalLoading, maxNewLoads) {
-  var newLoads = Math.min(
-      maxTotalLoading - this.getTilesLoading(), maxNewLoads, this.getCount());
-  var i, tile;
-  for (i = 0; i < newLoads; ++i) {
+  var newLoads = 0;
+  var tile;
+  while (this.tilesLoading_ < maxTotalLoading && newLoads < maxNewLoads &&
+         this.getCount() > 0) {
     tile = /** @type {ol.Tile} */ (this.dequeue()[0]);
-    goog.events.listen(tile, goog.events.EventType.CHANGE,
-        this.handleTileChange, false, this);
-    tile.load();
+    if (tile.getState() === ol.TileState.IDLE) {
+      goog.events.listen(tile, goog.events.EventType.CHANGE,
+          this.handleTileChange, false, this);
+      tile.load();
+      ++this.tilesLoading_;
+      ++newLoads;
+    }
   }
-  this.tilesLoading_ += newLoads;
 };

test/spec/ol/tilequeue.test.js

@@ -13,6 +13,73 @@ describe('ol.TileQueue', function() {
     }
   }
 
+  var tileId = 0;
+  function createImageTile() {
+    ++tileId;
+    var tileCoord = [tileId, tileId, tileId];
+    var state = ol.TileState.IDLE;
+    var src = 'data:image/gif;base64,R0lGODlhAQABAPAAAP8AAP///' +
+        'yH5BAAAAAAALAAAAAABAAEAAAICRAEAOw==#' + tileId;
+
+    return new ol.ImageTile(tileCoord, state, src, null,
+        ol.source.Image.defaultImageLoadFunction);
+  }
+
+  describe('#loadMoreTiles()', function() {
+    var noop = function() {};
+
+    it('works when tile queues share tiles', function(done) {
+      var q1 = new ol.TileQueue(noop, noop);
+      var q2 = new ol.TileQueue(noop, noop);
+
+      var numTiles = 20;
+      for (var i = 0; i < numTiles; ++i) {
+        var tile = createImageTile();
+        q1.enqueue([tile]);
+        q2.enqueue([tile]);
+      }
+
+      // Initially, both have all tiles.
+      expect(q1.getCount()).to.equal(numTiles);
+      expect(q2.getCount()).to.equal(numTiles);
+
+      var maxLoading = numTiles / 2;
+
+      // and nothing is loading
+      expect(q1.getTilesLoading()).to.equal(0);
+      expect(q2.getTilesLoading()).to.equal(0);
+
+      // ask both to load
+      q1.loadMoreTiles(maxLoading, maxLoading);
+      q2.loadMoreTiles(maxLoading, maxLoading);
+
+      // both tiles will be loading the max
+      expect(q1.getTilesLoading()).to.equal(maxLoading);
+      expect(q2.getTilesLoading()).to.equal(maxLoading);
+
+      // the second queue will be empty now
+      expect(q1.getCount()).to.equal(numTiles - maxLoading);
+      expect(q2.getCount()).to.equal(0);
+
+      // let all tiles load
+      setTimeout(function() {
+        expect(q1.getTilesLoading()).to.equal(0);
+        expect(q2.getTilesLoading()).to.equal(0);
+
+        // ask both to load, this should clear q1
+        q1.loadMoreTiles(maxLoading, maxLoading);
+        q2.loadMoreTiles(maxLoading, maxLoading);
+
+        expect(q1.getCount()).to.equal(0);
+        expect(q2.getCount()).to.equal(0);
+
+        done();
+      }, 20);
+
+    });
+
+  });
+
   describe('heapify', function() {
     it('does convert an arbitrary array into a heap', function() {
 
@@ -56,6 +123,9 @@ describe('ol.TileQueue', function() {
   });
 });
 
+goog.require('ol.ImageTile');
 goog.require('ol.Tile');
+goog.require('ol.TileState');
 goog.require('ol.TileQueue');
+goog.require('ol.source.Image');
 goog.require('ol.structs.PriorityQueue');