1 files changed, 238 insertions, 0 deletions
diff --git a/js/xpconnect/tests/browser/browser_weak_xpcwjs.js b/js/xpconnect/tests/browser/browser_weak_xpcwjs.js
new file mode 100644
index 0000000000..b8c8c2f85d
--- /dev/null
+++ b/js/xpconnect/tests/browser/browser_weak_xpcwjs.js
@@ -0,0 +1,238 @@
+/* Any copyright is dedicated to the Public Domain.
+   http://creativecommons.org/publicdomain/zero/1.0/ */
+
+"use strict";
+
+// Some basic tests of the lifetime of an XPCWJS with a weak reference.
+
+// Create a weak reference, with a single-element weak map.
+let make_weak_ref = function (obj) {
+  let m = new WeakMap();
+  m.set(obj, {});
+  return m;
+};
+
+// Check to see if a weak reference is dead.
+let weak_ref_dead = function (r) {
+  return !SpecialPowers.nondeterministicGetWeakMapKeys(r).length;
+};
+
+add_task(async function gc_wwjs() {
+  // This subtest checks that a WJS with only a weak reference to it gets
+  // cleaned up, if its JS object is garbage, after just a GC.
+  // For the browser, this probably isn't important, but tests seem to rely
+  // on it.
+  const TEST_PREF = "wjs.pref1";
+  let wjs_weak_ref = null;
+  let observed_count = 0;
+
+  {
+    Services.prefs.clearUserPref(TEST_PREF);
+
+    // Create the observer object.
+    let observer1 = {
+      QueryInterface: ChromeUtils.generateQI(["nsISupportsWeakReference"]),
+      observe() {
+        observed_count += 1;
+        info(TEST_PREF + " pref observer.");
+      },
+    };
+
+    // Register the weak observer.
+    Services.prefs.addObserver(TEST_PREF, observer1, true);
+
+    // Invoke the observer to make sure it is doing something.
+    info("Flipping the pref " + TEST_PREF);
+    Services.prefs.setBoolPref(TEST_PREF, true);
+    is(observed_count, 1, "Ran observer1 once after first flip.");
+
+    wjs_weak_ref = make_weak_ref(observer1);
+
+    // Exit the scope, making observer1 garbage.
+  }
+
+  // Run the GC.
+  info("Running the GC.");
+  SpecialPowers.forceGC();
+
+  // Flip the pref again to make sure that the observer doesn't run.
+  info("Flipping the pref " + TEST_PREF);
+  Services.prefs.setBoolPref(TEST_PREF, false);
+
+  is(observed_count, 1, "After GC, don't run the observer.");
+  ok(weak_ref_dead(wjs_weak_ref), "WJS with weak ref should be freed.");
+
+  Services.prefs.clearUserPref(TEST_PREF);
+});
+
+add_task(async function alive_wwjs() {
+  // This subtest checks that a WJS with only a weak reference should not get
+  // cleaned up if the underlying JS object is held alive (here, via the
+  // variable |observer2|).
+  const TEST_PREF = "wjs.pref2";
+  let observed_count = 0;
+
+  Services.prefs.clearUserPref(TEST_PREF);
+  let observer2 = {
+    QueryInterface: ChromeUtils.generateQI(["nsISupportsWeakReference"]),
+    observe() {
+      observed_count += 1;
+      info(TEST_PREF + " pref observer");
+    },
+  };
+  Services.prefs.addObserver(TEST_PREF, observer2, true);
+
+  Services.prefs.setBoolPref(TEST_PREF, true);
+  is(observed_count, 1, "Run observer2 once after first flip.");
+
+  await new Promise(resolve =>
+    SpecialPowers.exactGC(() => {
+      SpecialPowers.forceCC();
+      SpecialPowers.forceGC();
+      SpecialPowers.forceCC();
+
+      Services.prefs.setBoolPref(TEST_PREF, false);
+
+      is(observed_count, 2, "Run observer2 again after second flip.");
+
+      Services.prefs.removeObserver(TEST_PREF, observer2);
+      Services.prefs.clearUserPref(TEST_PREF);
+
+      resolve();
+    })
+  );
+});
+
+add_task(async function cc_wwjs() {
+  // This subtest checks that a WJS with only a weak reference to it, where the
+  // underlying JS object is part of a garbage cycle, gets cleaned up after a
+  // cycle collection. It also checks that things held alive by the JS object
+  // don't end up in an unlinked state, although that's mostly for fun, because
+  // it is redundant with checking that the JS object gets cleaned up.
+  const TEST_PREF = "wjs.pref3";
+  let wjs_weak_ref = null;
+  let observed_count = 0;
+  let canary_count;
+
+  {
+    Services.prefs.clearUserPref(TEST_PREF);
+
+    // Set up a canary object that lets us detect unlinking.
+    // (When an nsArrayCC is unlinked, all of the elements are removed.)
+    // This is needed to distinguish the case where the observer was unlinked
+    // without removing the weak reference from the case where we did not
+    // collect the observer at all.
+    let canary = Cc["@mozilla.org/array;1"].createInstance(Ci.nsIMutableArray);
+    let someString = Cc["@mozilla.org/supports-string;1"].createInstance(
+      Ci.nsISupportsString
+    );
+    someString.data = "canary";
+    canary.appendElement(someString);
+    canary.appendElement(someString);
+    is(canary.Count(), 2, "The canary array should have two elements");
+
+    // Create the observer object.
+    let observer3 = {
+      QueryInterface: ChromeUtils.generateQI(["nsISupportsWeakReference"]),
+      canary,
+      cycle: new DOMMatrix(),
+      observe() {
+        observed_count += 1;
+        canary_count = this.canary.Count();
+        info(TEST_PREF + " pref observer. Canary count: " + canary_count);
+      },
+    };
+
+    // Set up a cycle between C++ and JS that requires the CC to collect.
+    // |cycle| is a random WebIDL object that we can set an expando on to
+    // create a nice clean cycle that doesn't involve any weird XPConnect stuff.
+    observer3.cycle.backEdge = observer3;
+
+    // Register the weak observer.
+    Services.prefs.addObserver(TEST_PREF, observer3, true);
+
+    // Invoke the observer to make sure it is doing something.
+    info("Flipping the pref " + TEST_PREF);
+    canary_count = -1;
+    Services.prefs.setBoolPref(TEST_PREF, true);
+    is(
+      canary_count,
+      2,
+      "Observer ran with expected value while observer3 is alive."
+    );
+    is(observed_count, 1, "Ran observer3 once after first flip.");
+
+    wjs_weak_ref = make_weak_ref(observer3);
+
+    // Exit the scope, making observer3 and canary garbage.
+  }
+
+  // Run the GC. This is necessary to mark observer3 gray so the CC
+  // might consider it to be garbage. This won't free it because it is held
+  // alive from C++ (namely the DOMMatrix via its expando).
+  info("Running the GC.");
+  SpecialPowers.forceGC();
+
+  // Note: Don't flip the pref here. Doing so will run the observer, which will
+  // cause it to get marked black again, preventing it from being freed.
+  // For the same reason, don't call weak_ref_dead(wjs_weak_ref) here.
+
+  // Run the CC. This should detect that the cycle between observer3 and the
+  // DOMMatrix is garbage, unlinking the DOMMatrix and the canary. Also, the
+  // weak reference for the WJS for observer3 should get cleared because the
+  // underlying JS object has been identifed as garbage. You can add logging to
+  // nsArrayCC's unlink method to see the canary getting unlinked.
+  info("Running the CC.");
+  SpecialPowers.forceCC();
+
+  // Flip the pref again to make sure that the observer doesn't run.
+  info("Flipping the pref " + TEST_PREF);
+  canary_count = -1;
+  Services.prefs.setBoolPref(TEST_PREF, false);
+
+  isnot(
+    canary_count,
+    0,
+    "After CC, don't run the observer with an unlinked canary."
+  );
+  isnot(
+    canary_count,
+    2,
+    "After CC, don't run the observer after it is garbage."
+  );
+  is(canary_count, -1, "After CC, don't run the observer.");
+  is(observed_count, 1, "After CC, don't run the observer.");
+
+  ok(
+    !weak_ref_dead(wjs_weak_ref),
+    "WJS with weak ref shouldn't be freed by the CC."
+  );
+
+  // Now that the CC has identified observer3 as garbage, running the GC again
+  // should free it.
+  info("Running the GC again.");
+  SpecialPowers.forceGC();
+
+  ok(weak_ref_dead(wjs_weak_ref), "WJS with weak ref should be freed.");
+
+  info("Flipping the pref " + TEST_PREF);
+  canary_count = -1;
+  Services.prefs.setBoolPref(TEST_PREF, true);
+
+  // Note: the original implementation of weak references for WJS fails most of
+  // the prior canary_count tests, but passes these.
+  isnot(
+    canary_count,
+    0,
+    "After GC, don't run the observer with an unlinked canary."
+  );
+  isnot(
+    canary_count,
+    2,
+    "After GC, don't run the observer after it is garbage."
+  );
+  is(canary_count, -1, "After GC, don't run the observer.");
+  is(observed_count, 1, "After GC, don't run the observer.");
+
+  Services.prefs.clearUserPref(TEST_PREF);
+});