Bug 1559675 - P1. Initialize StaticPrefs early in non-parent process. r=njn

We can initialize the StaticPrefs as soon as the SharedMap object is created outside the parent process.

Additionally when resetting the preferences to their default values, we no longer modify the `Once` StaticPrefs as they are immutable, only the underlying preference.

Differential Revision: https://phabricator.services.mozilla.com/D35263

--HG--
extra : moz-landing-system : lando

modules/libpref/Preferences.cpp

@@ -3747,6 +3747,8 @@ void Preferences::InitSnapshot(const FileDescriptor& aHandle, size_t aSize) {
   MOZ_ASSERT(!gSharedMap);
 
   gSharedMap = new SharedPrefMap(aHandle, aSize);
+
+  StaticPrefs::InitStaticPrefsFromShared();
 }
 
 /* static */
@@ -4475,30 +4477,14 @@ struct PreferencesInternalMethods {
 
 // Initialize default preference JavaScript buffers from appropriate TEXT
 // resources.
-/* static */ Result<Ok, const char*> Preferences::InitInitialObjects(
-    bool aIsStartup) {
+/* static */
+Result<Ok, const char*> Preferences::InitInitialObjects(bool aIsStartup) {
   // Initialize static prefs before prefs from data files so that the latter
   // will override the former.
   StaticPrefs::InitAll(aIsStartup);
 
   if (!XRE_IsParentProcess()) {
-    MOZ_ASSERT(gSharedMap);
-
-    // We got our initial preference values from the content process, so we
-    // don't need to add them to the DB. For static var caches, though, the
-    // current preference values may differ from their static defaults. So we
-    // still need to notify callbacks for each of our shared prefs which have
-    // user values, of whose default values have changed since they were
-    // initialized.
-    for (auto& pref : gSharedMap->Iter()) {
-      if (pref.HasUserValue() || pref.DefaultChanged()) {
-        NotifyCallbacks(pref.Name(), PrefWrapper(pref));
-      }
-    }
-
-    if (aIsStartup) {
-      StaticPrefs::InitOncePrefsFromShared();
-    }
+    MOZ_DIAGNOSTIC_ASSERT(gSharedMap);
 
 #ifdef DEBUG
     // Check that all varcache preferences match their current values. This
@@ -5376,13 +5362,32 @@ static void InitVarCachePref(StaticPrefs::UpdatePolicy aPolicy,
                              const nsACString& aName, T* aCache,
                              StripAtomic<T> aDefaultValue, bool aIsStartup,
                              bool aSetValue) {
-  if (aSetValue) {
+  // aSetValue is set when we are running in the parent process.
+  // aIsStartup will be true when we first initialize the StaticPrefs and false
+  // when we want to reset the Preferences/StaticPrefs to their default value.
+
+  // InitVarCachePref is called under the following scenarios:
+  // aSetValue | aIsStartup | Action
+  // true      | true       | Set underlying preference and StaticPrefs to
+  //           |            | their default value, set callback for Live pref.
+  // true      | false      | reset underlying preference and StaticPref to
+  //           |            | default value.
+  // false     | true       | set callback for Live pref.
+  // false     | false      | none.
+  //
+  // We only set *aCache if the policy is Live as:
+  // 1- On startup, `Once` prefs will be initialized lazily in InitOncePrefs(),
+  // 2- After that, `Once` prefs are immutable.
+
+  if (aSetValue && MOZ_LIKELY(aPolicy != StaticPrefs::UpdatePolicy::Skip)) {
     SetPref(PromiseFlatCString(aName).get(), aDefaultValue);
+    if (MOZ_LIKELY(aPolicy == StaticPrefs::UpdatePolicy::Live)) {
+      *aCache = aDefaultValue;
+    }
   }
 
-  *aCache = aDefaultValue;
-  if (MOZ_LIKELY(aIsStartup) &&
-      MOZ_LIKELY(aPolicy == StaticPrefs::UpdatePolicy::Live)) {
+  if (MOZ_LIKELY(aPolicy == StaticPrefs::UpdatePolicy::Live) &&
+      MOZ_LIKELY(aIsStartup)) {
     AddVarCache(aCache, aName, aDefaultValue, true);
   }
 }
@@ -5522,12 +5527,11 @@ void StaticPrefs::InitOncePrefs() {
 #ifdef DEBUG
 #  define VARCACHE_PREF(policy, name, id, cpp_type, value)                    \
     if (UpdatePolicy::policy == UpdatePolicy::Once) {                         \
+      MOZ_ASSERT(gOnceStaticPrefsAntiFootgun);                                \
       StaticPrefs::sVarCache_##id = PreferencesInternalMethods::GetPref(      \
           name, StripAtomic<cpp_type>(value));                                \
       auto checkPref = [&]() {                                                \
-        if (!sOncePrefRead) {                                                 \
-          return;                                                             \
-        }                                                                     \
+        MOZ_ASSERT(sOncePrefRead);                                            \
         StripAtomic<cpp_type> staticPrefValue = StaticPrefs::id();            \
         StripAtomic<cpp_type> preferenceValue =                               \
             PreferencesInternalMethods::GetPref(                              \
@@ -5642,7 +5646,7 @@ void StaticPrefs::RegisterOncePrefs(SharedPrefMapBuilder& aBuilder) {
 }
 
 /* static */
-void StaticPrefs::InitOncePrefsFromShared() {
+void StaticPrefs::InitStaticPrefsFromShared() {
   MOZ_ASSERT(!XRE_IsParentProcess());
   MOZ_DIAGNOSTIC_ASSERT(gSharedMap,
                         "Must be called once gSharedMap has been created");
@@ -5653,22 +5657,33 @@ void StaticPrefs::InitOncePrefsFromShared() {
   //
   // we generate registration calls:
   //
-  //   if (UpdatePolicy::Once == UpdatePolicy::Once) {
+  //   if (UpdatePolicy::Once != UpdatePolicy::Skip) {
   //     int32_t val;
-  //     MOZ_DIAGNOSTIC_ALWAYS_TRUE(
-  //       NS_SUCCEEDED(PreferencesInternalMethods::GetSharedPrefValue(
-  //           ONCE_PREF_NAME(name), &val)));
+  //     nsresult rv;
+  //     if (UpdatePolicy::Once == UpdatePolicy::Once) {
+  //       rv = PreferencesInternalMethods::GetSharedPrefValue(
+  //           "$$$my.varcache$$$", &val);
+  //     } else if (UpdatePolicy::Once == UpdatePolicy::Live) {
+  //       rv = PreferencesInternalMethods::GetSharedPrefValue(
+  //           "my.varcache", &val);
+  //     }
+  //     MOZ_DIAGNOSTIC_ALWAYS_TRUE(NS_SUCCEEDED(rv));
   //     StaticPrefs::sVarCache_my_varcache = val;
   //   }
 
 #define PREF(name, cpp_type, value)
-#define VARCACHE_PREF(policy, name, id, cpp_type, value)             \
-  if (UpdatePolicy::policy == UpdatePolicy::Once) {                  \
-    StripAtomic<cpp_type> val;                                       \
-    MOZ_DIAGNOSTIC_ALWAYS_TRUE(                                      \
-        NS_SUCCEEDED(PreferencesInternalMethods::GetSharedPrefValue( \
-            ONCE_PREF_NAME(name), &val)));                           \
-    StaticPrefs::sVarCache_##id = val;                               \
+#define VARCACHE_PREF(policy, name, id, cpp_type, value)               \
+  if (UpdatePolicy::policy != UpdatePolicy::Skip) {                    \
+    StripAtomic<cpp_type> val;                                         \
+    nsresult rv;                                                       \
+    if (UpdatePolicy::policy == UpdatePolicy::Once) {                  \
+      rv = PreferencesInternalMethods::GetSharedPrefValue(             \
+          ONCE_PREF_NAME(name), &val);                                 \
+    } else {                                                           \
+      rv = PreferencesInternalMethods::GetSharedPrefValue(name, &val); \
+    }                                                                  \
+    MOZ_DIAGNOSTIC_ALWAYS_TRUE(NS_SUCCEEDED(rv));                      \
+    StaticPrefs::sVarCache_##id = val;                                 \
   }
 #include "mozilla/StaticPrefList.h"
 #undef PREF

modules/libpref/StaticPrefs.h

@@ -115,9 +115,9 @@ class StaticPrefs {
  private:
   friend class Preferences;
   static void InitAll(bool aIsStartup);
-  static void InitOncePrefs();
-  static void InitOncePrefsFromShared();
   static void MaybeInitOncePrefs();
+  static void InitOncePrefs();
+  static void InitStaticPrefsFromShared();
   static void RegisterOncePrefs(SharedPrefMapBuilder& aBuilder);
 };