Bug 1541819 - Record allocations of Target class. r=jdescottes

This records on Talos the number of allocated objects after creating, attaching and destroying a Tab Target.

Depends on D26107

Differential Revision: https://phabricator.services.mozilla.com/D26108

--HG--
extra : moz-landing-system : lando

devtools/client/framework/moz.build

@@ -5,6 +5,7 @@
 # file, You can obtain one at http://mozilla.org/MPL/2.0/.
 
 BROWSER_CHROME_MANIFESTS += [
+    'test/allocations/browser_allocations_target.ini',
     'test/browser.ini',
     'test/metrics/browser_metrics_debugger.ini',
     'test/metrics/browser_metrics_inspector.ini',

devtools/client/framework/test/allocations/browser_allocations_target.ini

@@ -0,0 +1,10 @@
+[DEFAULT]
+tags = devtools
+subsuite = devtools
+support-files =
+  !/devtools/shared/test-helpers/allocation-tracker.js
+
+# Each metrics tests is loaded in a separate .ini file. This way the test is executed
+# individually, without any other test being executed before or after.
+[browser_allocations_target.js]
+skip-if = os != 'linux' || debug || asan || pgo # Results should be platform agnostic - only run on linux64-opt

devtools/client/framework/test/allocations/browser_allocations_target.js

@@ -0,0 +1,106 @@
+const TEST_URL = "data:text/html;charset=UTF-8,<div>Target allocations test</div>";
+
+// Load the tracker very first in order to ensure tracking all objects created by DevTools.
+// Loader.jsm shouldn't be loaded, not any other DevTools module until an explicit user action.
+let tracker;
+{
+  const { DevToolsLoader } = ChromeUtils.import("resource://devtools/shared/Loader.jsm");
+  const loader = new DevToolsLoader();
+  loader.invisibleToDebugger = true;
+  const { allocationTracker } = loader.require("chrome://mochitests/content/browser/devtools/shared/test-helpers/allocation-tracker");
+  tracker = allocationTracker({ watchDevToolsGlobals: true });
+}
+
+// So that PERFHERDER data can be extracted from the logs.
+SimpleTest.requestCompleteLog();
+
+const {require} = ChromeUtils.import("resource://devtools/shared/Loader.jsm");
+
+const {TargetFactory} = require("devtools/client/framework/target");
+
+async function doGC() {
+  // In order to get stable results, we really have to do 3 GC attempts
+  // *and* do wait for 1s between each GC.
+  const numCycles = 3;
+  for (let i = 0; i < numCycles; i++) {
+    Cu.forceGC();
+    Cu.forceCC();
+    await new Promise(resolve => Cu.schedulePreciseShrinkingGC(resolve));
+
+    // eslint-disable-next-line mozilla/no-arbitrary-setTimeout
+    await new Promise(resolve => setTimeout(resolve, 1000));
+  }
+}
+
+async function addTab(url) {
+  const tab = BrowserTestUtils.addTab(gBrowser, url);
+  gBrowser.selectedTab = tab;
+  await BrowserTestUtils.browserLoaded(tab.linkedBrowser);
+  return tab;
+}
+
+async function testScript(tab) {
+  const target = await TargetFactory.forTab(tab);
+  await target.attach();
+
+  // eslint-disable-next-line mozilla/no-arbitrary-setTimeout
+  await new Promise(resolve => setTimeout(resolve, 1000));
+
+  await target.destroy();
+}
+
+add_task(async function() {
+  const tab = await addTab(TEST_URL);
+
+  // Run the test scenario first before recording in order to load all the
+  // modules. Otherwise they get reported as "still allocated" objects,
+  // whereas we do expect them to be kept in memory as they are loaded via
+  // the main DevTools loader, which keeps the module loaded until the
+  // shutdown of Firefox
+  await testScript(tab);
+
+  // Do a first pass of GC, to ensure all to-be-freed objects from the first run
+  // are really freed.
+  await doGC();
+
+  // Then, record what was already allocated, which should not be declared
+  // as potential leaks. For ex, there is all the modules already loaded
+  // in the main DevTools loader.
+  const totalBefore = tracker.stillAllocatedObjects();
+
+  // Now, run the test script. This time, we record this run.
+  await testScript(tab);
+
+  // After that, re-do some GCs in order to free all what is to-be-freed.
+  await doGC();
+
+  // Ensure that Memory API didn't ran out of buffers
+  ok(!tracker.overflowed, "Allocation were all recorded");
+
+  // And finally, retrieve the number of objects that are still allocated.
+  const totalAfter = tracker.stillAllocatedObjects();
+
+  gBrowser.removeTab(tab);
+
+  const PERFHERDER_DATA = {
+    framework: {
+      name: "devtools",
+    },
+    suites: [{
+      name: "total-after-gc",
+      value: totalAfter - totalBefore,
+      subtests: [
+        {
+          name: "before",
+          value: totalBefore,
+        },
+        {
+          name: "after",
+          value: totalAfter - totalBefore,
+        },
+      ],
+    }],
+  };
+  info("PERFHERDER_DATA: " + JSON.stringify(PERFHERDER_DATA));
+  ok(true, "Test succeeded");
+});