Bug 1126880 - FlameGraphUtils should have a cache to avoid duplicating work, r=jsantell

browser/devtools/shared/test/browser.ini

@@ -24,6 +24,7 @@ support-files =
 [browser_flame-graph-utils-02.js]
 [browser_flame-graph-utils-03.js]
 [browser_flame-graph-utils-04.js]
+[browser_flame-graph-utils-05.js]
 [browser_flame-graph-utils-hash.js]
 [browser_graphs-01.js]
 [browser_graphs-02.js]

browser/devtools/shared/test/browser_flame-graph-utils-05.js

@@ -0,0 +1,42 @@
+/* Any copyright is dedicated to the Public Domain.
+   http://creativecommons.org/publicdomain/zero/1.0/ */
+
+// Tests that flame graph data is cached, and that the cache may be cleared.
+
+let {FlameGraphUtils} = Cu.import("resource:///modules/devtools/FlameGraph.jsm", {});
+
+add_task(function*() {
+  yield promiseTab("about:blank");
+  yield performTest();
+  gBrowser.removeCurrentTab();
+});
+
+function* performTest() {
+  let out1 = FlameGraphUtils.createFlameGraphDataFromSamples(TEST_DATA);
+  let out2 = FlameGraphUtils.createFlameGraphDataFromSamples(TEST_DATA);
+  is(out1, out2, "The outputted data is identical.")
+
+  let out3 = FlameGraphUtils.createFlameGraphDataFromSamples(TEST_DATA, { flattenRecursion: true });
+  is(out2, out3, "The outputted data is still identical.");
+
+  FlameGraphUtils.removeFromCache(TEST_DATA);
+  let out4 = FlameGraphUtils.createFlameGraphDataFromSamples(TEST_DATA, { flattenRecursion: true });
+  isnot(out3, out4, "The outputted data is not identical anymore.");
+}
+
+let TEST_DATA = [{
+  frames: [{
+    location: "A"
+  }, {
+    location: "A"
+  }, {
+    location: "A"
+  }, {
+    location: "B",
+  }, {
+    location: "B",
+  }, {
+    location: "C"
+  }],
+  time: 50,
+}];

browser/devtools/shared/widgets/FlameGraph.jsm

@@ -856,10 +856,16 @@ const COLOR_PALLETTE = Array.from(Array(PALLETTE_SIZE)).map((_, i) => "hsla" +
  * into a format drawable by the FlameGraph.
  */
 let FlameGraphUtils = {
+  _cache: new WeakMap(),
+
   /**
    * Converts a list of samples from the profiler data to something that's
    * drawable by a FlameGraph widget.
    *
+   * The outputted data will be cached, so the next time this method is called
+   * the previous output is returned. If this is undesirable, or should the
+   * options change, use `removeFromCache`.
+   *
    * @param array samples
    *        A list of { time, frames: [{ location }] } objects.
    * @param object options [optional]
@@ -876,6 +882,11 @@ let FlameGraphUtils = {
    *         The flame graph data.
    */
   createFlameGraphDataFromSamples: function(samples, options = {}, out = []) {
+    let cached = this._cache.get(samples);
+    if (cached) {
+      return cached;
+    }
+
     // 1. Create a map of colors to arrays, representing buckets of
     // blocks inside the flame graph pyramid sharing the same style.
 
@@ -952,9 +963,18 @@ let FlameGraphUtils = {
       out.push({ color, blocks });
     }
 
+    this._cache.set(samples, out);
     return out;
   },
 
+  /**
+   * Clears the cached flame graph data created for the given source.
+   * @param any source
+   */
+  removeFromCache: function(source) {
+    this._cache.delete(source);
+  },
+
   /**
    * Checks if the provided frame is the same as the next one in a sample.
    *