Merge autoland to mozilla-central a=merge

browser/base/content/test/performance/PerfTestHelpers.jsm

@@ -0,0 +1,78 @@
+/* Any copyright is dedicated to the Public Domain.
+   http://creativecommons.org/publicdomain/zero/1.0/ */
+
+var EXPORTED_SYMBOLS = ["PerfTestHelpers"];
+
+const lazy = {};
+
+ChromeUtils.defineModuleGetter(
+  lazy,
+  "NetUtil",
+  "resource://gre/modules/NetUtil.jsm"
+);
+
+var PerfTestHelpers = {
+  /**
+   * Maps the entries in the given iterable to the given
+   * promise-returning task function, and waits for all returned
+   * promises to have resolved. At most `limit` promises may remain
+   * unresolved at a time. When the limit is reached, the function will
+   * wait for some to resolve before spawning more tasks.
+   */
+  async throttledMapPromises(iterable, task, limit = 64) {
+    let pending = new Set();
+    let promises = [];
+    for (let data of iterable) {
+      while (pending.size >= limit) {
+        await Promise.race(pending);
+      }
+
+      let promise = task(data);
+      promises.push(promise);
+      if (promise) {
+        promise.finally(() => pending.delete(promise));
+        pending.add(promise);
+      }
+    }
+
+    return Promise.all(promises);
+  },
+
+  /**
+   * Returns a promise which resolves to true if the resource at the
+   * given URI exists, false if it doesn't. This should only be used
+   * with local resources, such as from resource:/chrome:/jar:/file:
+   * URIs.
+   */
+  checkURIExists(uri) {
+    return new Promise(resolve => {
+      try {
+        let channel = lazy.NetUtil.newChannel({
+          uri,
+          loadUsingSystemPrincipal: true,
+        });
+
+        channel.asyncOpen({
+          onStartRequest(request) {
+            resolve(Components.isSuccessCode(request.status));
+            request.cancel(Cr.NS_BINDING_ABORTED);
+          },
+
+          onStopRequest(request, status) {
+            // We should have already resolved from `onStartRequest`, but
+            // we resolve again here just as a failsafe.
+            resolve(Components.isSuccessCode(status));
+          },
+        });
+      } catch (e) {
+        if (
+          e.result != Cr.NS_ERROR_FILE_NOT_FOUND &&
+          e.result != Cr.NS_ERROR_NOT_AVAILABLE
+        ) {
+          throw e;
+        }
+        resolve(false);
+      }
+    });
+  },
+};

browser/base/content/test/performance/browser_startup.js

@@ -57,8 +57,6 @@ const startupPhases = {
   "before first paint": {
     denylist: {
       modules: new Set([
-        "chrome://webcompat/content/data/ua_overrides.jsm",
-        "chrome://webcompat/content/lib/ua_overrider.jsm",
         "resource:///modules/AboutNewTab.jsm",
         "resource:///modules/BrowserUsageTelemetry.jsm",
         "resource:///modules/ContentCrashHandlers.jsm",
@@ -86,7 +84,6 @@ const startupPhases = {
         "resource://gre/modules/BookmarkHTMLUtils.jsm",
         "resource://gre/modules/Bookmarks.jsm",
         "resource://gre/modules/ContextualIdentityService.jsm",
-        "resource://gre/modules/CrashSubmit.jsm",
         "resource://gre/modules/FxAccounts.jsm",
         "resource://gre/modules/FxAccountsStorage.jsm",
         "resource://gre/modules/PlacesBackups.jsm",
@@ -94,10 +91,7 @@ const startupPhases = {
         "resource://gre/modules/PlacesSyncUtils.jsm",
         "resource://gre/modules/PushComponents.jsm",
       ]),
-      services: new Set([
-        "@mozilla.org/browser/annotation-service;1",
-        "@mozilla.org/browser/nav-bookmarks-service;1",
-      ]),
+      services: new Set(["@mozilla.org/browser/nav-bookmarks-service;1"]),
     },
   },
 
@@ -128,6 +122,12 @@ if (
   );
 }
 
+if (AppConstants.MOZ_CRASHREPORTER) {
+  startupPhases["before handling user events"].denylist.modules.add(
+    "resource://gre/modules/CrashSubmit.jsm"
+  );
+}
+
 add_task(async function() {
   if (
     !AppConstants.NIGHTLY_BUILD &&
@@ -219,6 +219,29 @@ add_task(async function() {
           }
         }
       }
+
+      if (denylist.modules) {
+        let results = await PerfTestHelpers.throttledMapPromises(
+          denylist.modules,
+          async uri => ({
+            uri,
+            exists: await PerfTestHelpers.checkURIExists(uri),
+          })
+        );
+
+        for (let { uri, exists } of results) {
+          ok(exists, `denylist entry ${uri} for phase "${phase}" must exist`);
+        }
+      }
+
+      if (denylist.services) {
+        for (let contract of denylist.services) {
+          ok(
+            contract in Cc,
+            `denylist entry ${contract} for phase "${phase}" must exist`
+          );
+        }
+      }
     }
   }
 });

browser/base/content/test/performance/browser_startup_content.js

@@ -170,7 +170,7 @@ add_task(async function() {
     loadedInfo.processScripts[uri] = "";
   }
 
-  checkLoadedScripts({
+  await checkLoadedScripts({
     loadedInfo,
     known: known_scripts,
     intermittent: intermittently_loaded_scripts,

browser/base/content/test/performance/browser_startup_content_subframe.js

@@ -141,7 +141,7 @@ add_task(async function() {
     loadedInfo.processScripts[uri] = "";
   }
 
-  checkLoadedScripts({
+  await checkLoadedScripts({
     loadedInfo,
     known: known_scripts,
     intermittent: intermittently_loaded_scripts,

browser/base/content/test/performance/browser_startup_images.js

@@ -82,6 +82,19 @@ add_task(async function() {
     return el.platforms.includes(AppConstants.platform);
   });
 
+  {
+    let results = await PerfTestHelpers.throttledMapPromises(
+      knownImagesForPlatform,
+      async image => ({
+        uri: image.file,
+        exists: await PerfTestHelpers.checkURIExists(image.file),
+      })
+    );
+    for (let { uri, exists } of results) {
+      ok(exists, `Unshown image entry ${uri} must exist`);
+    }
+  }
+
   let loadedImages = data["image-loading"];
   let shownImages = data["image-drawing"];
 

browser/base/content/test/performance/head.js

@@ -2,6 +2,7 @@
 
 XPCOMUtils.defineLazyModuleGetters(this, {
   AboutNewTab: "resource:///modules/AboutNewTab.jsm",
+  PerfTestHelpers: "resource://testing-common/PerfTestHelpers.jsm",
   PlacesTestUtils: "resource://testing-common/PlacesTestUtils.jsm",
   PlacesUtils: "resource://gre/modules/PlacesUtils.jsm",
   UrlbarTestUtils: "resource://testing-common/UrlbarTestUtils.jsm",
@@ -843,7 +844,7 @@ async function runUrlbarTest(
  *        If true, dump the stacks for all loaded modules. Makes the output
  *        noisy.
  */
-function checkLoadedScripts({
+async function checkLoadedScripts({
   loadedInfo,
   known,
   intermittent,
@@ -852,6 +853,32 @@ function checkLoadedScripts({
 }) {
   let loadedList = {};
 
+  async function checkAllExist(scriptType, list, listType) {
+    if (scriptType == "services") {
+      for (let contract of list) {
+        ok(
+          contract in Cc,
+          `${listType} entry ${contract} for content process startup must exist`
+        );
+      }
+    } else {
+      let results = await PerfTestHelpers.throttledMapPromises(
+        list,
+        async uri => ({
+          uri,
+          exists: await PerfTestHelpers.checkURIExists(uri),
+        })
+      );
+
+      for (let { uri, exists } of results) {
+        ok(
+          exists,
+          `${listType} entry ${uri} for content process startup must exist`
+        );
+      }
+    }
+  }
+
   for (let scriptType in known) {
     loadedList[scriptType] = Object.keys(loadedInfo[scriptType]).filter(c => {
       if (!known[scriptType].has(c)) {
@@ -880,6 +907,8 @@ function checkLoadedScripts({
       );
     }
 
+    await checkAllExist(scriptType, intermittent[scriptType], "intermittent");
+
     is(
       known[scriptType].size,
       0,
@@ -919,5 +948,7 @@ function checkLoadedScripts({
         );
       }
     }
+
+    await checkAllExist(scriptType, forbidden[scriptType], "forbidden");
   }
 }

browser/base/content/test/performance/moz.build

@@ -0,0 +1,17 @@
+# -*- Mode: python; indent-tabs-mode: nil; tab-width: 40 -*-
+# vim: set filetype=python:
+# This Source Code Form is subject to the terms of the Mozilla Public
+# License, v. 2.0. If a copy of the MPL was not distributed with this
+# file, You can obtain one at http://mozilla.org/MPL/2.0/.
+
+
+BROWSER_CHROME_MANIFESTS += [
+    "browser.ini",
+    "hidpi/browser.ini",
+    "io/browser.ini",
+    "lowdpi/browser.ini",
+]
+
+TESTING_JS_MODULES += [
+    "PerfTestHelpers.jsm",
+]

browser/base/content/test/static/browser_all_files_referenced.js

@@ -744,30 +744,13 @@ function convertToCodeURI(fileUri) {
   }
 }
 
-function chromeFileExists(aURI) {
-  let available = 0;
+async function chromeFileExists(aURI) {
   try {
-    let channel = NetUtil.newChannel({
-      uri: aURI,
-      loadUsingSystemPrincipal: true,
-      contentPolicyType: Ci.nsIContentPolicy.TYPE_FETCH,
-    });
-    let stream = channel.open();
-    let sstream = Cc["@mozilla.org/scriptableinputstream;1"].createInstance(
-      Ci.nsIScriptableInputStream
-    );
-    sstream.init(stream);
-    available = sstream.available();
-    sstream.close();
+    return await PerfTestHelpers.checkURIExists(aURI);
   } catch (e) {
-    if (
-      e.result != Cr.NS_ERROR_FILE_NOT_FOUND &&
-      e.result != Cr.NS_ERROR_NOT_AVAILABLE
-    ) {
-      todo(false, "Failed to check if " + aURI + "exists: " + e);
+    todo(false, `Failed to check if ${aURI} exists: ${e}`);
+    return false;
   }
-  }
-  return available > 0;
 }
 
 function findChromeUrlsFromArray(array, prefix) {
@@ -875,7 +858,7 @@ add_task(async function checkAllTheFiles() {
   });
 
   // Wait for all manifest to be parsed
-  await throttledMapPromises(manifestURIs, parseManifest);
+  await PerfTestHelpers.throttledMapPromises(manifestURIs, parseManifest);
 
   for (let jsm of Components.manager.getComponentJSMs()) {
     gReferencesFromCode.set(jsm, null);
@@ -908,7 +891,9 @@ add_task(async function checkAllTheFiles() {
   }
 
   // Wait for all the files to have actually loaded:
-  await throttledMapPromises(allPromises, ([task, uri]) => task(uri));
+  await PerfTestHelpers.throttledMapPromises(allPromises, ([task, uri]) =>
+    task(uri)
+  );
 
   // Keep only chrome:// files, and filter out either the devtools paths or
   // the non-devtools paths:
@@ -1069,7 +1054,7 @@ add_task(async function checkAllTheFiles() {
 
     if (
       (file.startsWith("chrome://") || file.startsWith("resource://")) &&
-      !chromeFileExists(file)
+      !(await chromeFileExists(file))
     ) {
       // Ignore chrome prefixes that have been automatically expanded.
       let pathParts =

browser/base/content/test/static/browser_parsable_css.js

@@ -437,7 +437,7 @@ add_task(async function checkAllTheCSS() {
     return true;
   });
   // Wait for all manifest to be parsed
-  await throttledMapPromises(manifestURIs, parseManifest);
+  await PerfTestHelpers.throttledMapPromises(manifestURIs, parseManifest);
 
   // filter out either the devtools paths or the non-devtools paths:
   let isDevtools = SimpleTest.harnessParameters.subsuite == "devtools";
@@ -488,7 +488,7 @@ add_task(async function checkAllTheCSS() {
   }
 
   // Wait for all the files to have actually loaded:
-  await throttledMapPromises(allPromises, loadCSS);
+  await PerfTestHelpers.throttledMapPromises(allPromises, loadCSS);
 
   // Check if all the files referenced from CSS actually exist.
   // Files in browser/ should never be referenced outside browser/.

browser/base/content/test/static/browser_parsable_script.js

@@ -153,7 +153,7 @@ add_task(async function checkAllTheJS() {
 
   // We create an array of promises so we can parallelize all our parsing
   // and file loading activity:
-  await throttledMapPromises(uris, uri => {
+  await PerfTestHelpers.throttledMapPromises(uris, uri => {
     if (uriIsWhiteListed(uri)) {
       info("Not checking whitelisted " + uri.spec);
       return undefined;

browser/base/content/test/static/head.js

@@ -17,6 +17,9 @@ const ZipReader = new Components.Constructor(
 
 const IS_ALPHA = /^[a-z]+$/i;
 
+var { PerfTestHelpers } = ChromeUtils.import(
+  "resource://testing-common/PerfTestHelpers.jsm"
+);
 var { Services } = ChromeUtils.import("resource://gre/modules/Services.jsm");
 var { OS, require } = ChromeUtils.import("resource://gre/modules/osfile.jsm");
 
@@ -157,23 +160,6 @@ function fetchFile(uri) {
   });
 }
 
-async function throttledMapPromises(iterable, task, limit = 64) {
-  let promises = new Set();
-  for (let data of iterable) {
-    while (promises.size >= limit) {
-      await Promise.race(promises);
-    }
-
-    let promise = task(data);
-    if (promise) {
-      promise.finally(() => promises.delete(promise));
-      promises.add(promise);
-    }
-  }
-
-  await Promise.all(promises);
-}
-
 /**
  * Returns whether or not a word (presumably in en-US) is capitalized per
  * expectations.

browser/base/moz.build

@@ -39,10 +39,6 @@ BROWSER_CHROME_MANIFESTS += [
     "content/test/pageActions/browser.ini",
     "content/test/pageinfo/browser.ini",
     "content/test/pageStyle/browser.ini",
-    "content/test/performance/browser.ini",
-    "content/test/performance/hidpi/browser.ini",
-    "content/test/performance/io/browser.ini",
-    "content/test/performance/lowdpi/browser.ini",
     "content/test/permissions/browser.ini",
     "content/test/plugins/browser.ini",
     "content/test/popupNotifications/browser.ini",
@@ -71,6 +67,10 @@ BROWSER_CHROME_MANIFESTS += [
     "content/test/zoom/browser.ini",
 ]
 
+DIRS += [
+    "content/test/performance/",
+]
+
 PERFTESTS_MANIFESTS += ["content/test/perftest.ini"]
 
 DEFINES["MOZ_APP_VERSION"] = CONFIG["MOZ_APP_VERSION"]

browser/components/urlbar/UrlbarProviderAutofill.jsm

@@ -778,16 +778,20 @@ class ProviderAutofill extends UrlbarProvider {
       queryType != QUERYTYPE.AUTOFILL_ORIGIN &&
       queryContext.searchString.length == autofilledValue.length
     ) {
+      // Use `new URL().href` to lowercase the domain in the final completed
+      // URL. This isn't necessary since domains are case insensitive, but it
+      // looks nicer because it means the domain will remain lowercased in the
+      // input, and it also reflects the fact that Firefox will visit the
+      // lowercased name.
       const originalCompleteValue = new URL(finalCompleteValue).href;
-      // Make sure the domain is lowercased in the final URL. This isn't
-      // necessary since domains are case insensitive, but it looks nicer
-      // because it means the domain will remain lowercased in the input, and it
-      // also reflects the fact that Firefox will visit the lowercased name.
+      let strippedAutofilledValue = autofilledValue.substring(
+        this._strippedPrefix.length
+      );
       finalCompleteValue = new URL(
         finalCompleteValue.substring(
           0,
-          finalCompleteValue.length - autofilledValue.length
-        ) + autofilledValue
+          finalCompleteValue.length - strippedAutofilledValue.length
+        ) + strippedAutofilledValue
       ).href;
 
       // If the character case of except origin part of the original

browser/components/urlbar/tests/unit/test_autofill_urls.js

@@ -814,3 +814,95 @@ add_task(async function aboutAsPrefix() {
 
   await cleanupPlaces();
 });
+
+// Checks a URL that has www name in history.
+add_task(async function wwwHistory() {
+  const testData = [
+    {
+      input: "example.com/",
+      visitHistory: [{ uri: "http://www.example.com/", title: "Example" }],
+      expected: {
+        autofilled: "example.com/",
+        completed: "http://www.example.com/",
+        hasAutofillTitle: true,
+        results: [
+          context =>
+            makeVisitResult(context, {
+              uri: "http://www.example.com/",
+              title: "Example",
+              heuristic: true,
+            }),
+        ],
+      },
+    },
+    {
+      input: "https://example.com/",
+      visitHistory: [{ uri: "https://www.example.com/", title: "Example" }],
+      expected: {
+        autofilled: "https://example.com/",
+        completed: "https://www.example.com/",
+        hasAutofillTitle: true,
+        results: [
+          context =>
+            makeVisitResult(context, {
+              uri: "https://www.example.com/",
+              title: "Example",
+              heuristic: true,
+            }),
+        ],
+      },
+    },
+    {
+      input: "https://example.com/abc",
+      visitHistory: [{ uri: "https://www.example.com/abc", title: "Example" }],
+      expected: {
+        autofilled: "https://example.com/abc",
+        completed: "https://www.example.com/abc",
+        hasAutofillTitle: true,
+        results: [
+          context =>
+            makeVisitResult(context, {
+              uri: "https://www.example.com/abc",
+              title: "Example",
+              heuristic: true,
+            }),
+        ],
+      },
+    },
+    {
+      input: "https://example.com/ABC",
+      visitHistory: [{ uri: "https://www.example.com/abc", title: "Example" }],
+      expected: {
+        autofilled: "https://example.com/ABC",
+        completed: "https://www.example.com/ABC",
+        hasAutofillTitle: false,
+        results: [
+          context =>
+            makeVisitResult(context, {
+              uri: "https://www.example.com/ABC",
+              title: "https://www.example.com/ABC",
+              heuristic: true,
+            }),
+          context =>
+            makeVisitResult(context, {
+              uri: "https://www.example.com/abc",
+              title: "Example",
+            }),
+        ],
+      },
+    },
+  ];
+
+  for (const { input, visitHistory, expected } of testData) {
+    await PlacesTestUtils.addVisits(visitHistory);
+    const context = createContext(input, { isPrivate: false });
+    await check_results({
+      context,
+      completed: expected.completed,
+      autofilled: expected.autofilled,
+      hasAutofillTitle: expected.hasAutofillTitle,
+      matches: expected.results.map(f => f(context)),
+    });
+    await cleanupPlaces();
+  }
+});

build/clang-plugin/ThreadAllows.txt

@@ -12,6 +12,7 @@ COM Intcpt Log
 COM MTA
 Cache I/O
 Cameras IPC
+CanvasRenderer
 ChainedPipePump
 ChainedPipeRecv
 Checker Test

gfx/config/gfxVars.h

@@ -92,7 +92,8 @@ class gfxVarReceiver;
   _(UseVP9HwDecode, bool, false)                                   \
   _(HwDecodedVideoZeroCopy, bool, false)                           \
   _(UseDMABufSurfaceExport, bool, true)                            \
-  _(ReuseDecoderDevice, bool, false)
+  _(ReuseDecoderDevice, bool, false)                               \
+  _(UseCanvasRenderThread, bool, false)
 
 /* Add new entries above this line. */
 

gfx/ipc/CanvasManagerParent.cpp

@@ -6,6 +6,7 @@
 
 #include "CanvasManagerParent.h"
 #include "mozilla/dom/WebGLParent.h"
+#include "mozilla/gfx/CanvasRenderThread.h"
 #include "mozilla/gfx/gfxVars.h"
 #include "mozilla/ipc/Endpoint.h"
 #include "mozilla/layers/CompositorThread.h"
@@ -23,9 +24,7 @@ CanvasManagerParent::ManagerSet CanvasManagerParent::sManagers;
 
   auto manager = MakeRefPtr<CanvasManagerParent>();
 
-  if (gfxVars::SupportsThreadsafeGL()) {
-    manager->Bind(std::move(aEndpoint));
-  } else {
+  if (!gfxVars::SupportsThreadsafeGL()) {
     nsCOMPtr<nsIThread> owningThread;
     owningThread = wr::RenderThread::GetRenderThread();
     MOZ_ASSERT(owningThread);
@@ -33,6 +32,16 @@ CanvasManagerParent::ManagerSet CanvasManagerParent::sManagers;
     owningThread->Dispatch(NewRunnableMethod<Endpoint<PCanvasManagerParent>&&>(
         "CanvasManagerParent::Bind", manager, &CanvasManagerParent::Bind,
         std::move(aEndpoint)));
+  } else if (gfxVars::UseCanvasRenderThread()) {
+    nsCOMPtr<nsIThread> owningThread;
+    owningThread = gfx::CanvasRenderThread::GetCanvasRenderThread();
+    MOZ_ASSERT(owningThread);
+
+    owningThread->Dispatch(NewRunnableMethod<Endpoint<PCanvasManagerParent>&&>(
+        "CanvasManagerParent::Bind", manager, &CanvasManagerParent::Bind,
+        std::move(aEndpoint)));
+  } else {
+    manager->Bind(std::move(aEndpoint));
   }
 }
 
@@ -40,10 +49,12 @@ CanvasManagerParent::ManagerSet CanvasManagerParent::sManagers;
   MOZ_ASSERT(NS_IsMainThread());
 
   nsCOMPtr<nsISerialEventTarget> owningThread;
-  if (gfxVars::SupportsThreadsafeGL()) {
-    owningThread = layers::CompositorThread();
-  } else {
+  if (!gfxVars::SupportsThreadsafeGL()) {
     owningThread = wr::RenderThread::GetRenderThread();
+  } else if (gfxVars::UseCanvasRenderThread()) {
+    owningThread = gfx::CanvasRenderThread::GetCanvasRenderThread();
+  } else {
+    owningThread = layers::CompositorThread();
   }
   if (!owningThread) {
     return;

gfx/ipc/CanvasRenderThread.cpp

@@ -0,0 +1,111 @@
+/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* vim: set ts=8 sts=2 et sw=2 tw=80: */
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+#include "CanvasRenderThread.h"
+
+#include "mozilla/BackgroundHangMonitor.h"
+#include "transport/runnable_utils.h"
+
+namespace mozilla::gfx {
+
+static StaticRefPtr<CanvasRenderThread> sCanvasRenderThread;
+static mozilla::BackgroundHangMonitor* sBackgroundHangMonitor;
+
+CanvasRenderThread::CanvasRenderThread(RefPtr<nsIThread> aThread)
+    : mThread(std::move(aThread)) {}
+
+CanvasRenderThread::~CanvasRenderThread() {}
+
+// static
+CanvasRenderThread* CanvasRenderThread::Get() { return sCanvasRenderThread; }
+
+// static
+void CanvasRenderThread::Start() {
+  MOZ_ASSERT(NS_IsMainThread());
+  MOZ_ASSERT(!sCanvasRenderThread);
+
+  // This is 512K, which is higher than the default 256K.
+  // Increased to accommodate Mesa in bug 1753340.
+  //
+  // Previously increased to 320K to avoid a stack overflow in the
+  // Intel Vulkan driver initialization in bug 1716120.
+  //
+  // Note: we only override it if it's limited already.
+  const uint32_t stackSize =
+      nsIThreadManager::DEFAULT_STACK_SIZE ? 512 << 10 : 0;
+
+  RefPtr<nsIThread> thread;
+  nsresult rv = NS_NewNamedThread(
+      "CanvasRenderer", getter_AddRefs(thread),
+      NS_NewRunnableFunction(
+          "CanvasRender::BackgroundHanSetup",
+          []() {
+            sBackgroundHangMonitor = new mozilla::BackgroundHangMonitor(
+                "CanvasRenderer",
+                /* Timeout values are powers-of-two to enable us get better
+                   data. 128ms is chosen for transient hangs because 8Hz should
+                   be the minimally acceptable goal for Compositor
+                   responsiveness (normal goal is 60Hz). */
+                128,
+                /* 2048ms is chosen for permanent hangs because it's longer than
+                 * most Compositor hangs seen in the wild, but is short enough
+                 * to not miss getting native hang stacks. */
+                2048);
+            nsCOMPtr<nsIThread> thread = NS_GetCurrentThread();
+            nsThread* nsthread = static_cast<nsThread*>(thread.get());
+            nsthread->SetUseHangMonitor(true);
+            nsthread->SetPriority(nsISupportsPriority::PRIORITY_HIGH);
+          }),
+      stackSize);
+
+  if (NS_FAILED(rv)) {
+    return;
+  }
+
+  sCanvasRenderThread = new CanvasRenderThread(thread);
+}
+
+// static
+void CanvasRenderThread::ShutDown() {
+  MOZ_ASSERT(NS_IsMainThread());
+  MOZ_ASSERT(sCanvasRenderThread);
+
+  layers::SynchronousTask task("CanvasRenderThread");
+  RefPtr<Runnable> runnable =
+      WrapRunnable(RefPtr<CanvasRenderThread>(sCanvasRenderThread.get()),
+                   &CanvasRenderThread::ShutDownTask, &task);
+  sCanvasRenderThread->PostRunnable(runnable.forget());
+  task.Wait();
+
+  sCanvasRenderThread = nullptr;
+}
+
+void CanvasRenderThread::ShutDownTask(layers::SynchronousTask* aTask) {
+  layers::AutoCompleteTask complete(aTask);
+  MOZ_ASSERT(IsInCanvasRenderThread());
+}
+
+// static
+bool CanvasRenderThread::IsInCanvasRenderThread() {
+  return sCanvasRenderThread &&
+         sCanvasRenderThread->mThread == NS_GetCurrentThread();
+}
+
+// static
+already_AddRefed<nsIThread> CanvasRenderThread::GetCanvasRenderThread() {
+  nsCOMPtr<nsIThread> thread;
+  if (sCanvasRenderThread) {
+    thread = sCanvasRenderThread->mThread;
+  }
+  return thread.forget();
+}
+
+void CanvasRenderThread::PostRunnable(already_AddRefed<nsIRunnable> aRunnable) {
+  nsCOMPtr<nsIRunnable> runnable = aRunnable;
+  mThread->Dispatch(runnable.forget());
+}
+
+}  // namespace mozilla::gfx

gfx/ipc/CanvasRenderThread.h

@@ -0,0 +1,50 @@
+/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* vim: set ts=8 sts=2 et sw=2 tw=80: */
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+#ifndef _include_gfx_ipc_CanvasRenderThread_h__
+#define _include_gfx_ipc_CanvasRenderThread_h__
+
+#include "mozilla/DataMutex.h"
+#include "mozilla/layers/SynchronousTask.h"
+#include "mozilla/StaticPtr.h"
+#include "nsISupportsImpl.h"
+#include "nsThread.h"
+
+namespace mozilla::gfx {
+
+class CanvasRenderThread final {
+  NS_INLINE_DECL_THREADSAFE_REFCOUNTING_WITH_DELETE_ON_MAIN_THREAD(
+      CanvasRenderThread)
+
+ public:
+  /// Can be called from any thread.
+  static CanvasRenderThread* Get();
+
+  /// Can only be called from the main thread.
+  static void Start();
+
+  /// Can only be called from the main thread.
+  static void ShutDown();
+
+  /// Can be called from any thread.
+  static bool IsInCanvasRenderThread();
+
+  /// Can be called from any thread.
+  static already_AddRefed<nsIThread> GetCanvasRenderThread();
+
+ private:
+  explicit CanvasRenderThread(RefPtr<nsIThread> aThread);
+  ~CanvasRenderThread();
+
+  void ShutDownTask(layers::SynchronousTask* aTask);
+  void PostRunnable(already_AddRefed<nsIRunnable> aRunnable);
+
+  RefPtr<nsIThread> const mThread;
+};
+
+}  // namespace mozilla::gfx
+
+#endif  // _include_gfx_ipc_CanvasRenderThread_h__

gfx/ipc/GPUParent.cpp

@@ -38,6 +38,7 @@
 #include "mozilla/TimeStamp.h"
 #include "mozilla/dom/MemoryReportRequest.h"
 #include "mozilla/gfx/2D.h"
+#include "mozilla/gfx/CanvasRenderThread.h"
 #include "mozilla/gfx/gfxVars.h"
 #include "mozilla/glean/GleanMetrics.h"
 #include "mozilla/image/ImageMemoryReporter.h"
@@ -360,6 +361,9 @@ mozilla::ipc::IPCResult GPUParent::RecvInit(
 
   // Make sure to do this *after* we update gfxVars above.
   if (gfxVars::UseWebRender()) {
+    if (gfxVars::UseCanvasRenderThread()) {
+      gfx::CanvasRenderThread::Start();
+    }
     wr::RenderThread::Start(aWrNamespace);
     image::ImageMemoryReporter::InitForWebRender();
   }
@@ -695,6 +699,9 @@ void GPUParent::ActorDestroy(ActorDestroyReason aWhy) {
         if (wr::RenderThread::Get()) {
           wr::RenderThread::ShutDown();
         }
+        if (gfx::CanvasRenderThread::Get()) {
+          gfx::CanvasRenderThread::ShutDown();
+        }
 #ifdef XP_WIN
         if (widget::WinCompositorWindowThread::Get()) {
           widget::WinCompositorWindowThread::ShutDown();

gfx/ipc/moz.build

@@ -12,6 +12,7 @@ EXPORTS.mozilla += ["D3DMessageUtils.h", "GfxMessageUtils.h"]
 EXPORTS.mozilla.gfx += [
     "CanvasManagerChild.h",
     "CanvasManagerParent.h",
+    "CanvasRenderThread.h",
     "CrossProcessPaint.h",
     "GPUChild.h",
     "GPUParent.h",
@@ -39,6 +40,7 @@ EXPORTS.mozilla.widget += [
 UNIFIED_SOURCES += [
     "CanvasManagerChild.cpp",
     "CanvasManagerParent.cpp",
+    "CanvasRenderThread.cpp",
     "CompositorSession.cpp",
     "CompositorWidgetVsyncObserver.cpp",
     "CrossProcessPaint.cpp",

gfx/thebes/gfxPlatform.cpp

@@ -22,6 +22,7 @@
 #include "mozilla/gfx/GraphicsMessages.h"
 #include "mozilla/gfx/CanvasManagerChild.h"
 #include "mozilla/gfx/CanvasManagerParent.h"
+#include "mozilla/gfx/CanvasRenderThread.h"
 #include "mozilla/ClearOnShutdown.h"
 #include "mozilla/StaticPrefs_accessibility.h"
 #include "mozilla/StaticPrefs_apz.h"
@@ -1291,6 +1292,9 @@ void gfxPlatform::InitLayersIPC() {
 #endif
     if (!gfxConfig::IsEnabled(Feature::GPU_PROCESS) && UseWebRender()) {
       RemoteTextureMap::Init();
+      if (gfxVars::UseCanvasRenderThread()) {
+        gfx::CanvasRenderThread::Start();
+      }
       wr::RenderThread::Start(GPUProcessManager::Get()->AllocateNamespace());
       image::ImageMemoryReporter::InitForWebRender();
     }
@@ -1340,6 +1344,9 @@ void gfxPlatform::ShutdownLayersIPC() {
           nsDependentCString(
               StaticPrefs::GetPrefName_gfx_webrender_blob_tile_size()));
     }
+    if (gfx::CanvasRenderThread::Get()) {
+      gfx::CanvasRenderThread::ShutDown();
+    }
 #if defined(XP_WIN)
     widget::WinWindowOcclusionTracker::ShutDown();
 #endif
@@ -2854,6 +2861,10 @@ void gfxPlatform::InitWebGLConfig() {
   threadsafeGL &= !StaticPrefs::webgl_threadsafe_gl_force_disabled_AtStartup();
   gfxVars::SetSupportsThreadsafeGL(threadsafeGL);
 
+  bool useCanvasRenderThread =
+      threadsafeGL && StaticPrefs::webgl_use_canvas_render_thread_AtStartup();
+  gfxVars::SetUseCanvasRenderThread(useCanvasRenderThread);
+
   if (kIsAndroid) {
     // Don't enable robust buffer access on Adreno 630 devices.
     // It causes the linking of some shaders to fail. See bug 1485441.
@@ -3520,6 +3531,9 @@ void gfxPlatform::DisableGPUProcess() {
 
   RemoteTextureMap::Init();
   if (gfxVars::UseWebRender()) {
+    if (gfxVars::UseCanvasRenderThread()) {
+      gfx::CanvasRenderThread::Start();
+    }
     // We need to initialize the parent process to prepare for WebRender if we
     // did not end up disabling it, despite losing the GPU process.
     wr::RenderThread::Start(GPUProcessManager::Get()->AllocateNamespace());

modules/libpref/init/StaticPrefList.yaml

@@ -13480,6 +13480,11 @@
   value: false
   mirror: once
 
+- name: webgl.use-canvas-render-thread
+  type: bool
+  value: @IS_NOT_ANDROID@
+  mirror: once
+
 - name: webgl.override-unmasked-renderer
   type: String
   value: ""