From 5755a94b869116219f891e1c275379c7791ef170 Mon Sep 17 00:00:00 2001
From: Anny Gakhokidze <agakhokidze@mozilla.com>
Date: Fri, 28 Aug 2020 17:20:57 +0000
Subject: [PATCH] Bug 1589102 - Part 7: Fix
 test_browsing_context_structured_clone.js to instead schedule precise gc,
 r=kmag

Differential Revision: https://phabricator.services.mozilla.com/D85086
---
 .../test_browsing_context_structured_clone.js | 23 ++++++++-----------
 testing/xpcshell/head.js                      | 12 ++++++++++
 2 files changed, 22 insertions(+), 13 deletions(-)

diff --git a/docshell/test/unit/test_browsing_context_structured_clone.js b/docshell/test/unit/test_browsing_context_structured_clone.js
index ebd27b09752b..d06f7aecf601 100644
--- a/docshell/test/unit/test_browsing_context_structured_clone.js
+++ b/docshell/test/unit/test_browsing_context_structured_clone.js
@@ -4,7 +4,11 @@ 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);
+
+  await new Promise(r => {
+    frame.onload = () => r();
+    browser.document.body.appendChild(frame);
+  });
 
   let { browsingContext } = frame;
 
@@ -39,11 +43,6 @@ add_task(async function test_BrowsingContext_structured_clone() {
   // 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;
@@ -52,13 +51,11 @@ add_task(async function test_BrowsingContext_structured_clone() {
   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();
+  // We will schedule a precise GC and do both GC and CC a few times, to make
+  // sure we have completely destroyed the WindowGlobal actors (which keep
+  // references to their BrowsingContexts) in order
+  // to allow their (now snow-white) references to be collected.
+  await schedulePreciseGCAndForceCC(3);
 
   // OK. We can be fairly confident that the BrowsingContext object
   // stored in our structured clone data has been destroyed. Make sure
diff --git a/testing/xpcshell/head.js b/testing/xpcshell/head.js
index ccab0d1175db..1bbadde6953f 100644
--- a/testing/xpcshell/head.js
+++ b/testing/xpcshell/head.js
@@ -1463,6 +1463,18 @@ function do_send_remote_message(name, data) {
   mm[sender](name, data);
 }
 
+/**
+ * Schedules and awaits a precise GC, and forces CC, `maxCount` number of times.
+ * @param maxCount
+ *        How many times GC and CC should be scheduled.
+ */
+async function schedulePreciseGCAndForceCC(maxCount) {
+  for (let count = 0; count < maxCount; count++) {
+    await new Promise(resolve => Cu.schedulePreciseGC(resolve));
+    Cu.forceCC();
+  }
+}
+
 /**
  * Add a test function to the list of tests that are to be run asynchronously.
  *