test_weak_observer.js

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

"use strict";

// Tests that preference helpers work properly with custom types of Float and Json.

const { PrefObserver } = require("devtools/client/shared/prefs");
// Use sinon for mocking.
const {sinon} = ChromeUtils.import("resource://testing-common/Sinon.jsm");

const AUTO_CLOSE = "devtools.editor.autoclosebrackets";
const TAB_SIZE = "devtools.editor.tabsize";

add_task(async function testPrefObserver() {
  info("Init pref to a given value");
  Services.prefs.setBoolPref(AUTO_CLOSE, false);
  Services.prefs.setIntPref(TAB_SIZE, 2);

  const prefObserver = new PrefObserver("devtools.editor.");

  const autoCloseBracketSpy = sinon.spy();
  prefObserver.on(AUTO_CLOSE, autoCloseBracketSpy);

  const tabSizeSpy = sinon.spy();
  prefObserver.on(TAB_SIZE, tabSizeSpy);

  Services.prefs.setBoolPref(AUTO_CLOSE, true);
  Services.prefs.setIntPref(TAB_SIZE, 3);
  Services.prefs.setBoolPref(AUTO_CLOSE, false);
  Services.prefs.setIntPref(TAB_SIZE, 9);
  Services.prefs.setBoolPref(AUTO_CLOSE, true);

  is(tabSizeSpy.callCount, 2, `${TAB_SIZE} observer was called as expected`);
  is(autoCloseBracketSpy.callCount, 3, `${AUTO_CLOSE} observer was called as expected`);

  prefObserver.destroy();

  const weakPrefObserver = new PrefObserver("devtools.editor.", true);
  weakPrefObserver.on(AUTO_CLOSE, autoCloseBracketSpy);
  Services.prefs.setBoolPref(AUTO_CLOSE, false);
  is(autoCloseBracketSpy.callCount, 4, `${AUTO_CLOSE} observer was called as expected`);

  weakPrefObserver.destroy();
  Services.prefs.setBoolPref(AUTO_CLOSE, true);
  is(autoCloseBracketSpy.callCount, 4, `${AUTO_CLOSE} observer was called as expected`);

  createAnotherWeakObserver(autoCloseBracketSpy);
  await forceGC();
  Services.prefs.setBoolPref(AUTO_CLOSE, false);
  // should be immediately removed since nobody has a reference on this observer.
  is(autoCloseBracketSpy.callCount, 4, `${AUTO_CLOSE} observer was called as expected`);

  let obj = {};
  obj.referencedWeakObserver = createAnotherWeakObserver(autoCloseBracketSpy);
  await forceGC();
  Services.prefs.setBoolPref(AUTO_CLOSE, true);
  // should be caught since we have reference on the observer this time.
  is(autoCloseBracketSpy.callCount, 5, `${AUTO_CLOSE} observer was called as expected`);

  obj.referencedWeakObserver = null;
  delete obj.referencedWeakObserver;
  obj = null;
  await forceGC();
  await forceGC();
  await forceGC();
  Services.prefs.setBoolPref(AUTO_CLOSE, false);
  // I would expect the observer to be gone after so many GC, but it's still called.
  is(autoCloseBracketSpy.callCount, 5, `${AUTO_CLOSE} observer was called as expected`);
});

function createAnotherWeakObserver(spy) {
  const weakPrefObserver = new PrefObserver("devtools.editor.", true);
  weakPrefObserver.on(AUTO_CLOSE, spy);
  return weakPrefObserver;
}

async function forceGC() {
  for (let i = 0; i < 3; i++) {
    // See minimizeMemoryUsage code here to justify the GC+CC+GC:
    // https://searchfox.org/mozilla-central/rev/be78e6ea9b10b1f5b2b3b013f01d86e1062abb2b/dom/base/nsJSEnvironment.cpp#341-349
    Cu.forceGC();
    Cu.forceCC();
    Cu.forceGC();
    await new Promise(done => setTimeout(done, 0));
  }
}