fune/docshell/test/unit/test_browsing_context_structured_clone.js

"use strict";

add_task(async function test_BrowsingContext_structured_clone() {
  let browser = Services.appShell.createWindowlessBrowser(false);

  let frame = browser.document.createElement("iframe");
  browser.document.body.appendChild(frame);

  let {browsingContext} = frame;

  let sch = new StructuredCloneHolder({browsingContext});

  let deserialize = () => sch.deserialize({}, true);

  // Check that decoding a live browsing context produces the correct
  // object.
  equal(deserialize().browsingContext, browsingContext,
        "Got correct browsing context from StructuredClone deserialize");

  // Check that decoding a second time still succeeds.
  equal(deserialize().browsingContext, browsingContext,
        "Got correct browsing context from second StructuredClone deserialize");

  // Destroy the browsing context and make sure that the decode fails
  // with a DataCloneError.
  //
  // Making sure the BrowsingContext is actually destroyed by the time
  // we do the second decode is a bit tricky. We obviously have clear
  // our local references to it, and give the GC a chance to reap them.
  // And we also, of course, have to destroy the frame that it belongs
  // to, or its frame loader and window global would hold it alive.
  //
  // Beyond that, we don't *have* to reload or destroy the parent
  // document, but we do anyway just to be safe.
  //
  // Then comes the tricky bit: The WindowGlobal actors (which keep
  // references to their BrowsingContexts) require an IPC round trip to
  // be completely destroyed, even though they're in-process, so we make
  // a quick trip through the event loop, and then run the CC in order
  // to allow their (now snow-white) references to be collected.

  frame.remove();
  frame = null;
  browsingContext = null;

  browser.document.location.reload();
  browser.close();

  Cu.forceGC();

  // Give the IPC messages that destroy the actors a chance to be
  // processed.
  await new Promise(executeSoon);

  Cu.forceCC();

  // OK. We can be fairly confident that the BrowsingContext object
  // stored in our structured clone data has been destroyed. Make sure
  // that attempting to decode it again leads to the appropriate error.
  Assert.throws(deserialize, e => e.name === "DataCloneError",
                "Should get a DataCloneError when trying to decode a dead BrowsingContext");
});