Bug 1640087: Part 2: tuck optimized prefetches behind a preference. r=dthayer,aklotz

PrefetchRegistryInfo is intended to be a temporary file in order to conduct
this experiment on startup times vs. retention.
Most of the implementation is similar to LauncherRegistryInfo.
If we startup and the registry is different than the preference,
we will want to use the preference for the purpose of this experiment.

Differential Revision: https://phabricator.services.mozilla.com/D76993

Author: Emma Malysz

toolkit/xre/DllPrefetchExperimentRegistryInfo.cpp

@@ -0,0 +1,112 @@
+/* -*- 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 https://mozilla.org/MPL/2.0/. */
+
+#include "DllPrefetchExperimentRegistryInfo.h"
+
+#include "mozilla/Assertions.h"
+#include "mozilla/NativeNt.h"
+#include "mozilla/ResultExtensions.h"
+
+namespace mozilla {
+
+const wchar_t DllPrefetchExperimentRegistryInfo::kExperimentSubKeyPath[] =
+    L"SOFTWARE"
+    L"\\" MOZ_APP_VENDOR L"\\" MOZ_APP_BASENAME L"\\DllPrefetchExperiment";
+
+Result<Ok, nsresult> DllPrefetchExperimentRegistryInfo::Open() {
+  if (!!mRegKey) {
+    return Ok();
+  }
+
+  DWORD disposition;
+  HKEY rawKey;
+  LSTATUS result = ::RegCreateKeyExW(
+      HKEY_CURRENT_USER, kExperimentSubKeyPath, 0, nullptr,
+      REG_OPTION_NON_VOLATILE, KEY_ALL_ACCESS, nullptr, &rawKey, &disposition);
+
+  if (result != ERROR_SUCCESS) {
+    return Err(NS_ERROR_UNEXPECTED);
+  }
+
+  mRegKey.own(rawKey);
+
+  if (disposition == REG_CREATED_NEW_KEY ||
+      disposition == REG_OPENED_EXISTING_KEY) {
+    return Ok();
+  }
+
+  MOZ_ASSERT_UNREACHABLE("Invalid disposition from RegCreateKeyExW");
+  return Err(NS_ERROR_UNEXPECTED);
+}
+
+Result<Ok, nsresult> DllPrefetchExperimentRegistryInfo::ReflectPrefToRegistry(
+    int32_t aVal) {
+  MOZ_TRY(Open());
+
+  mPrefetchMode = aVal;
+
+  LSTATUS status =
+      ::RegSetValueExW(mRegKey.get(), mBinPath.get(), 0, REG_DWORD,
+                       reinterpret_cast<PBYTE>(&aVal), sizeof(aVal));
+
+  if (status != ERROR_SUCCESS) {
+    return Err(NS_ERROR_UNEXPECTED);
+  }
+
+  return Ok();
+}
+
+Result<Ok, nsresult> DllPrefetchExperimentRegistryInfo::ReadRegistryValueData(
+    DWORD expectedType) {
+  MOZ_TRY(Open());
+
+  int32_t data;
+  DWORD dataLen = sizeof((ULONG)data);
+  DWORD type;
+  LSTATUS status =
+      ::RegQueryValueExW(mRegKey.get(), mBinPath.get(), nullptr, &type,
+                         reinterpret_cast<PBYTE>(&data), &dataLen);
+
+  if (status == ERROR_FILE_NOT_FOUND) {
+    // The registry key has not been created, set to default 0
+    mPrefetchMode = 0;
+    return Ok();
+  }
+
+  if (status != ERROR_SUCCESS) {
+    return Err(NS_ERROR_UNEXPECTED);
+  }
+
+  if (type != expectedType) {
+    return Err(NS_ERROR_UNEXPECTED);
+  }
+
+  mPrefetchMode = data;
+  return Ok();
+}
+
+AlteredDllPrefetchMode
+DllPrefetchExperimentRegistryInfo::GetAlteredDllPrefetchMode() {
+  Result<Ok, nsresult> result = ReadRegistryValueData(REG_DWORD);
+  if (!result.isOk()) {
+    MOZ_ASSERT(false);
+    return AlteredDllPrefetchMode::CurrentPrefetch;
+  }
+
+  switch (mPrefetchMode) {
+    case 0:
+      return AlteredDllPrefetchMode::CurrentPrefetch;
+    case 1:
+      return AlteredDllPrefetchMode::NoPrefetch;
+    case 2:
+      return AlteredDllPrefetchMode::OptimizedPrefetch;
+    default:
+      MOZ_ASSERT(false);
+      return AlteredDllPrefetchMode::CurrentPrefetch;
+  }
+}
+
+}  // namespace mozilla

toolkit/xre/DllPrefetchExperimentRegistryInfo.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 https://mozilla.org/MPL/2.0/. */
+
+#ifndef mozilla_DllPrefetchExperimentRegistryInfo_h
+#define mozilla_DllPrefetchExperimentRegistryInfo_h
+
+#include "mozilla/Maybe.h"
+#include "mozilla/WinHeaderOnlyUtils.h"
+#include "nsWindowsHelpers.h"
+
+/**
+ * This is a temporary file in order to conduct an experiment on the impact of
+ * startup time on retention (see Bug 1640087).
+ * This was generally adapted from LauncherRegistryInfo.h
+ */
+
+namespace mozilla {
+
+enum class AlteredDllPrefetchMode {
+  CurrentPrefetch,
+  NoPrefetch,
+  OptimizedPrefetch
+};
+
+class DllPrefetchExperimentRegistryInfo final {
+ public:
+  DllPrefetchExperimentRegistryInfo() : mBinPath(GetFullBinaryPath().get()) {}
+  ~DllPrefetchExperimentRegistryInfo() {}
+
+  Result<Ok, nsresult> ReflectPrefToRegistry(int32_t aVal);
+  Result<Ok, nsresult> ReadRegistryValueData(DWORD expectedType);
+
+  AlteredDllPrefetchMode GetAlteredDllPrefetchMode();
+
+ private:
+  Result<Ok, nsresult> Open();
+
+  nsAutoRegKey mRegKey;
+  nsString mBinPath;
+  int32_t mPrefetchMode;
+
+  static const wchar_t kExperimentSubKeyPath[];
+};
+
+}  // namespace mozilla
+
+#endif  // mozilla_DllPrefetchExperimentRegistryInfo_h

toolkit/xre/moz.build

@@ -47,6 +47,7 @@ if CONFIG['MOZ_INSTRUMENT_EVENT_LOOP']:
 if CONFIG['MOZ_WIDGET_TOOLKIT'] == 'windows':
     EXPORTS.mozilla += [
         'AssembleCmdLine.h',
+        'DllPrefetchExperimentRegistryInfo.h',
         'ModuleVersionInfo.h',
         'PolicyChecks.h',
         'UntrustedModulesProcessor.h',
@@ -55,6 +56,7 @@ if CONFIG['MOZ_WIDGET_TOOLKIT'] == 'windows':
     ]
     UNIFIED_SOURCES += [
         '/toolkit/mozapps/update/common/updateutils_win.cpp',
+        'DllPrefetchExperimentRegistryInfo.cpp',
         'ModuleEvaluator.cpp',
         'ModuleVersionInfo.cpp',
         'nsNativeAppSupportWin.cpp',

toolkit/xre/nsAppRunner.cpp

@@ -101,6 +101,7 @@
 #  include <intrin.h>
 #  include <math.h>
 #  include "cairo/cairo-features.h"
+#  include "mozilla/DllPrefetchExperimentRegistryInfo.h"
 #  include "mozilla/WindowsDllBlocklist.h"
 #  include "mozilla/WindowsProcessMitigations.h"
 #  include "mozilla/WinHeaderOnlyUtils.h"
@@ -1561,6 +1562,28 @@ static void RegisterApplicationRestartChanged(const char* aPref, void* aData) {
   }
 }
 
+static void OnAlteredPrefetchPrefChanged(const char* aPref, void* aData) {
+  int32_t prefVal = Preferences::GetInt(PREF_WIN_ALTERED_DLL_PREFETCH, 0);
+
+  mozilla::DllPrefetchExperimentRegistryInfo prefetchRegInfo;
+  mozilla::DebugOnly<mozilla::Result<Ok, nsresult>> reflectResult =
+      prefetchRegInfo.ReflectPrefToRegistry(prefVal);
+
+  MOZ_ASSERT(reflectResult.value.isOk());
+}
+
+static void SetupAlteredPrefetchPref() {
+  mozilla::DllPrefetchExperimentRegistryInfo prefetchRegInfo;
+
+  mozilla::DebugOnly<mozilla::Result<Ok, nsresult>> reflectResult =
+      prefetchRegInfo.ReflectPrefToRegistry(
+          Preferences::GetInt(PREF_WIN_ALTERED_DLL_PREFETCH, 0));
+  MOZ_ASSERT(reflectResult.value.isOk());
+
+  Preferences::RegisterCallback(&OnAlteredPrefetchPrefChanged,
+                                PREF_WIN_ALTERED_DLL_PREFETCH);
+}
+
 #  if defined(MOZ_LAUNCHER_PROCESS)
 
 static void OnLauncherPrefChanged(const char* aPref, void* aData) {
@@ -3600,14 +3623,12 @@ static void ReadAheadSystemDll(const wchar_t* dllName) {
   }
 }
 
-#  ifdef NIGHTLY_BUILD
 static void ReadAheadPackagedDll(const wchar_t* dllName,
                                  const wchar_t* aGREDir) {
   wchar_t dllPath[MAX_PATH];
   swprintf(dllPath, MAX_PATH, L"%s\\%s", aGREDir, dllName);
   ReadAheadLib(dllPath);
 }
-#  endif
 
 static void PR_CALLBACK ReadAheadDlls_ThreadStart(void* arg) {
   UniquePtr<wchar_t[]> greDir(static_cast<wchar_t*>(arg));
@@ -3618,32 +3639,32 @@ static void PR_CALLBACK ReadAheadDlls_ThreadStart(void* arg) {
   // retention (see Bug 1640087). Before we place this within a pref,
   // we should ensure this feature only ships to the nightly channel
   // and monitor results from that subset.
-#  ifdef NIGHTLY_BUILD
-  // Prefetch the DLLs shipped with firefox
-  ReadAheadPackagedDll(L"libegl.dll", greDir.get());
-  ReadAheadPackagedDll(L"libGLESv2.dll", greDir.get());
-  ReadAheadPackagedDll(L"nssckbi.dll", greDir.get());
-  ReadAheadPackagedDll(L"freebl3.dll", greDir.get());
-  ReadAheadPackagedDll(L"softokn3.dll", greDir.get());
-
-  // Prefetch the system DLLs
-  ReadAheadSystemDll(L"DWrite.dll");
-  ReadAheadSystemDll(L"D3DCompiler_47.dll");
-#  else
-  // Load DataExchange.dll and twinapi.appcore.dll for
-  // nsWindow::EnableDragDrop
-  ReadAheadSystemDll(L"DataExchange.dll");
-  ReadAheadSystemDll(L"twinapi.appcore.dll");
+  if (greDir) {
+    // Prefetch the DLLs shipped with firefox
+    ReadAheadPackagedDll(L"libegl.dll", greDir.get());
+    ReadAheadPackagedDll(L"libGLESv2.dll", greDir.get());
+    ReadAheadPackagedDll(L"nssckbi.dll", greDir.get());
+    ReadAheadPackagedDll(L"freebl3.dll", greDir.get());
+    ReadAheadPackagedDll(L"softokn3.dll", greDir.get());
+
+    // Prefetch the system DLLs
+    ReadAheadSystemDll(L"DWrite.dll");
+    ReadAheadSystemDll(L"D3DCompiler_47.dll");
+  } else {
+    // Load DataExchange.dll and twinapi.appcore.dll for
+    // nsWindow::EnableDragDrop
+    ReadAheadSystemDll(L"DataExchange.dll");
+    ReadAheadSystemDll(L"twinapi.appcore.dll");
 
-  // Load twinapi.dll for WindowsUIUtils::UpdateTabletModeState
-  ReadAheadSystemDll(L"twinapi.dll");
+    // Load twinapi.dll for WindowsUIUtils::UpdateTabletModeState
+    ReadAheadSystemDll(L"twinapi.dll");
 
-  // Load explorerframe.dll for WinTaskbar::Initialize
-  ReadAheadSystemDll(L"ExplorerFrame.dll");
+    // Load explorerframe.dll for WinTaskbar::Initialize
+    ReadAheadSystemDll(L"ExplorerFrame.dll");
 
-  // Load WinTypes.dll for nsOSHelperAppService::GetApplicationDescription
-  ReadAheadSystemDll(L"WinTypes.dll");
-#  endif
+    // Load WinTypes.dll for nsOSHelperAppService::GetApplicationDescription
+    ReadAheadSystemDll(L"WinTypes.dll");
+  }
 }
 #endif
 
@@ -4335,14 +4356,29 @@ nsresult XREMain::XRE_mainRun() {
   }
 
 #ifdef XP_WIN
-  if (!PR_GetEnv("XRE_NO_DLL_READAHEAD")) {
+  mozilla::DllPrefetchExperimentRegistryInfo prefetchRegInfo;
+  mozilla::AlteredDllPrefetchMode dllPrefetchMode =
+      prefetchRegInfo.GetAlteredDllPrefetchMode();
+
+  if (!PR_GetEnv("XRE_NO_DLL_READAHEAD") &&
+      dllPrefetchMode != mozilla::AlteredDllPrefetchMode::NoPrefetch) {
     nsCOMPtr<nsIFile> greDir = mDirProvider.GetGREDir();
     nsAutoString path;
     rv = greDir->GetPath(path);
     if (NS_SUCCEEDED(rv)) {
       PRThread* readAheadThread;
-      wchar_t* pathRaw = new wchar_t[MAX_PATH];
-      wcscpy_s(pathRaw, MAX_PATH, path.get());
+      wchar_t* pathRaw;
+
+      // We use the presence of a path argument inside the thread to determine
+      // which list of Dlls to use. The old list does not need access to the
+      // GRE dir, so the path argument is set to a null pointer.
+      if (dllPrefetchMode ==
+          mozilla::AlteredDllPrefetchMode::OptimizedPrefetch) {
+        pathRaw = new wchar_t[MAX_PATH];
+        wcscpy_s(pathRaw, MAX_PATH, path.get());
+      } else {
+        pathRaw = nullptr;
+      }
       readAheadThread = PR_CreateThread(
           PR_USER_THREAD, ReadAheadDlls_ThreadStart, (void*)pathRaw,
           PR_PRIORITY_NORMAL, PR_GLOBAL_THREAD, PR_UNJOINABLE_THREAD, 0);
@@ -4550,6 +4586,7 @@ nsresult XREMain::XRE_mainRun() {
 #ifdef XP_WIN
     Preferences::RegisterCallbackAndCall(RegisterApplicationRestartChanged,
                                          PREF_WIN_REGISTER_APPLICATION_RESTART);
+    SetupAlteredPrefetchPref();
 #  if defined(MOZ_LAUNCHER_PROCESS)
     SetupLauncherProcessPref();
 #  endif  // defined(MOZ_LAUNCHER_PROCESS)

toolkit/xre/nsAppRunner.h

@@ -124,6 +124,8 @@ BOOL WinLaunchChild(const wchar_t* exePath, int argc, char** argv,
 #  define PREF_WIN_REGISTER_APPLICATION_RESTART \
     "toolkit.winRegisterApplicationRestart"
 
+#  define PREF_WIN_ALTERED_DLL_PREFETCH "startup.experiments.alteredDllPrefetch"
+
 #  if defined(MOZ_LAUNCHER_PROCESS)
 #    define PREF_WIN_LAUNCHER_PROCESS_ENABLED "browser.launcherProcess.enabled"
 #  endif  // defined(MOZ_LAUNCHER_PROCESS)