gecko-dev/devtools/shared/test-helpers/browser_allocation_tracker.js

/* Any copyright is dedicated to the Public Domain.
 * http://creativecommons.org/publicdomain/zero/1.0/ */

"use strict";

// Load the tracker in a dedicated loader using invisibleToDebugger and freshCompartment
// so that it can inspect any other module/compartment, even DevTools, chrome,
// and this script!
const { DevToolsLoader } = ChromeUtils.import(
  "resource://devtools/shared/Loader.jsm"
);
const loader = new DevToolsLoader({
  invisibleToDebugger: true,
  freshCompartment: true,
});
const { allocationTracker } = loader.require(
  "chrome://mochitests/content/browser/devtools/shared/test-helpers/allocation-tracker"
);

add_task(async function() {
  // Use a sandbox to allocate test javascript object in order to avoid any
  // external noise
  const global = Cu.Sandbox("http://example.com");

  const tracker = allocationTracker({ watchGlobal: global });
  const before = tracker.stillAllocatedObjects();

  /* eslint-disable no-undef */
  Cu.evalInSandbox(
    "let list; new " +
      function() {
        list = [];
        for (let i = 0; i < 1000; i++) {
          list.push({});
        }
      },
    global,
    undefined,
    "test-file.js",
    1
  );
  /* eslint-enable no-undef */

  const allocations = tracker.countAllocations();
  ok(
    allocations > 1000,
    `At least 1000 objects are reported as created (${allocations})`
  );

  // Uncomment this and comment the call to `countAllocations` to debug the allocations.
  // The call to `countAllocations` will reset the allocation record.
  // tracker.logAllocationSites();

  const afterCreation = tracker.stillAllocatedObjects();
  ok(
    afterCreation - before > 1000,
    `At least 1000 more objects are reported still allocated (${before}` +
      ` + ${afterCreation - before} -> ${afterCreation})`
  );

  Cu.evalInSandbox("list = null;", global, undefined, "test-file.js", 7);

  Cu.forceGC();
  Cu.forceCC();

  const afterGC = tracker.stillAllocatedObjects();
  ok(
    afterCreation - afterGC > 1000,
    `At least 1000 less objects are reported still allocated (${afterCreation}` +
      ` -(${afterGC - afterCreation})-> ${afterGC})`
  );

  tracker.stop();
});