Bug 1438732 - Use nsClassHashtable for prefs hashtable. r=njn

--HG--
extra : rebase_source : a17b9490b6d52d2ed4e510f27a2410f56724f861

modules/libpref/Preferences.cpp

@@ -326,9 +326,8 @@ static ArenaAllocator<8192, 1> gPrefNameArena;
 class Pref
 {
 public:
-  explicit Pref(const char* aName)
-    : mName(ArenaStrdup(aName, gPrefNameArena))
-    , mType(static_cast<uint32_t>(PrefType::None))
+  explicit Pref()
+    : mType(static_cast<uint32_t>(PrefType::None))
     , mIsSticky(false)
     , mIsLocked(false)
     , mHasDefaultValue(false)
@@ -341,15 +340,10 @@ public:
 
   ~Pref()
   {
-    // There's no need to free mName because it's allocated in memory owned by
-    // gPrefNameArena.
-
     mDefaultValue.Clear(Type());
     mUserValue.Clear(Type());
   }
 
-  const char* Name() { return mName; }
-
   // Types.
 
   PrefType Type() const { return static_cast<PrefType>(mType); }
@@ -401,15 +395,6 @@ public:
 
   // Other operations.
 
-  bool MatchEntry(const char* aPrefName)
-  {
-    if (!mName || !aPrefName) {
-      return false;
-    }
-
-    return strcmp(mName, aPrefName) == 0;
-  }
-
   nsresult GetBoolValue(PrefValueKind aKind, bool* aResult)
   {
     if (!IsTypeBool()) {
@@ -469,11 +454,16 @@ public:
     return NS_OK;
   }
 
-  void ToDomPref(dom::Pref* aDomPref)
+  // Fills out a dom pref with the values from this pref.
+  // @param aDomPref The pref to update.
+  // @param aName Optional. Override the dom pref's name with aName.
+  void ToDomPref(dom::Pref* aDomPref, const char* aName = nullptr)
   {
     MOZ_ASSERT(XRE_IsParentProcess());
 
-    aDomPref->name() = mName;
+    if (aName) {
+      aDomPref->name() = aName;
+    }
 
     aDomPref->isLocked() = mIsLocked;
 
@@ -502,7 +492,6 @@ public:
   void FromDomPref(const dom::Pref& aDomPref, bool* aValueChanged)
   {
     MOZ_ASSERT(!XRE_IsParentProcess());
-    MOZ_ASSERT(strcmp(mName, aDomPref.name().get()) == 0);
 
     mIsLocked = aDomPref.isLocked();
 
@@ -688,7 +677,6 @@ public:
 
   void AddSizeOfIncludingThis(MallocSizeOf aMallocSizeOf, PrefsSizes& aSizes)
   {
-    // Note: mName is allocated in gPrefNameArena, measured elsewhere.
     aSizes.mPrefValues += aMallocSizeOf(this);
     if (IsTypeString()) {
       if (mHasDefaultValue) {
@@ -701,8 +689,6 @@ public:
   }
 
 private:
-  const char* mName; // allocated in gPrefNameArena
-
   uint32_t mType : 2;
   uint32_t mIsSticky : 1;
   uint32_t mIsLocked : 1;
@@ -714,36 +700,6 @@ private:
   PrefValue mUserValue;
 };
 
-class PrefEntry : public PLDHashEntryHdr
-{
-public:
-  Pref* mPref;  // Note: this is never null in a live entry.
-
-  static bool MatchEntry(const PLDHashEntryHdr* aEntry, const void* aKey)
-  {
-    auto entry = static_cast<const PrefEntry*>(aEntry);
-    auto prefName = static_cast<const char*>(aKey);
-
-    return entry->mPref->MatchEntry(prefName);
-  }
-
-  static void InitEntry(PLDHashEntryHdr* aEntry, const void* aKey)
-  {
-    auto entry = static_cast<PrefEntry*>(aEntry);
-    auto prefName = static_cast<const char*>(aKey);
-
-    entry->mPref = new Pref(prefName);
-  }
-
-  static void ClearEntry(PLDHashTable* aTable, PLDHashEntryHdr* aEntry)
-  {
-    auto entry = static_cast<PrefEntry*>(aEntry);
-
-    delete entry->mPref;
-    entry->mPref = nullptr;
-  }
-};
-
 struct CallbackNode
 {
   CallbackNode(const char* aDomain,
@@ -769,7 +725,21 @@ struct CallbackNode
   CallbackNode* mNext;
 };
 
-static PLDHashTable* gHashTable;
+// Hash key that allocates its string from the `gPrefNameArena`. The base class
+// `nsDepCharHashKey` does not own the string data and no copies are made.
+class StringArenaHashKey : public nsDepCharHashKey
+{
+public:
+  explicit StringArenaHashKey(const char* aKey)
+    : nsDepCharHashKey(ArenaStrdup(aKey, gPrefNameArena))
+  {
+  }
+};
+
+// Hashtable used to map names to pref objects. StringArenaHashKey is used to
+// allocate the strings out of an arena.
+using PrefsTable = nsClassHashtable<StringArenaHashKey, Pref>;
+static PrefsTable* gHashTable;
 
 // The callback list contains all the priority callbacks followed by the
 // non-priority callbacks. gLastPriorityNode records where the first part ends.
@@ -782,14 +752,6 @@ static bool gIsAnyPrefLocked = false;
 static bool gCallbacksInProgress = false;
 static bool gShouldCleanupDeadNodes = false;
 
-static PLDHashTableOps pref_HashTableOps = {
-  PLDHashTable::HashStringKey,
-  PrefEntry::MatchEntry,
-  PLDHashTable::MoveEntryStub,
-  PrefEntry::ClearEntry,
-  PrefEntry::InitEntry,
-};
-
 static Pref*
 pref_HashTableLookup(const char* aPrefName);
 
@@ -803,10 +765,10 @@ pref_savePrefs()
 {
   MOZ_ASSERT(NS_IsMainThread());
 
-  PrefSaveData savedPrefs(gHashTable->EntryCount());
+  PrefSaveData savedPrefs(gHashTable->Count());
 
   for (auto iter = gHashTable->Iter(); !iter.Done(); iter.Next()) {
-    Pref* pref = static_cast<PrefEntry*>(iter.Get())->mPref;
+    Pref* pref = iter.Data();
 
     nsAutoCString prefValueStr;
     if (!pref->UserValueToStringForSaving(prefValueStr)) {
@@ -814,7 +776,7 @@ pref_savePrefs()
     }
 
     nsAutoCString prefNameStr;
-    StrEscape(pref->Name(), prefNameStr);
+    StrEscape(iter.Key(), prefNameStr);
 
     nsPrintfCString str(
       "user_pref(%s, %s);", prefNameStr.get(), prefValueStr.get());
@@ -865,7 +827,7 @@ IsEarlyPref(const char* aPrefName)
 
 #endif // DEBUG
 
-static PrefEntry*
+static PrefsTable::LookupResult
 pref_HashTableLookupInner(const char* aPrefName)
 {
   MOZ_ASSERT(NS_IsMainThread() || mozilla::ServoStyleSet::IsInServoTraversal());
@@ -888,14 +850,14 @@ pref_HashTableLookupInner(const char* aPrefName)
   }
 #endif
 
-  return static_cast<PrefEntry*>(gHashTable->Search(aPrefName));
+  return gHashTable->Lookup(aPrefName);
 }
 
 static Pref*
 pref_HashTableLookup(const char* aPrefName)
 {
-  PrefEntry* entry = pref_HashTableLookupInner(aPrefName);
-  return entry ? entry->mPref : nullptr;
+  PrefsTable::LookupResult entry = pref_HashTableLookupInner(aPrefName);
+  return entry ? static_cast<Pref*>(entry.Data()) : nullptr;
 }
 
 static nsresult
@@ -912,12 +874,7 @@ pref_SetPref(const char* aPrefName,
     return NS_ERROR_OUT_OF_MEMORY;
   }
 
-  auto entry = static_cast<PrefEntry*>(gHashTable->Add(aPrefName, fallible));
-  if (!entry) {
-    return NS_ERROR_OUT_OF_MEMORY;
-  }
-
-  Pref* pref = entry->mPref;
+  Pref* pref = gHashTable->LookupOrAdd(aPrefName);
   if (pref->IsTypeNone()) {
     // New entry. Set the type.
     pref->SetType(aType);
@@ -2030,13 +1987,11 @@ nsPrefBranch::DeleteBranch(const char* aStartingAt)
     Substring(branchName, 0, branchName.Length() - 1);
 
   for (auto iter = gHashTable->Iter(); !iter.Done(); iter.Next()) {
-    Pref* pref = static_cast<PrefEntry*>(iter.Get())->mPref;
-
     // The first disjunct matches branches: e.g. a branch name "foo.bar."
     // matches a name "foo.bar.baz" (but it won't match "foo.barrel.baz").
     // The second disjunct matches leaf nodes: e.g. a branch name "foo.bar."
     // matches a name "foo.bar" (by ignoring the trailing '.').
-    nsDependentCString name(pref->Name());
+    nsDependentCString name(iter.Key());
     if (StringBeginsWith(name, branchName) || name.Equals(branchNameNoDot)) {
       iter.Remove();
     }
@@ -2071,9 +2026,8 @@ nsPrefBranch::GetChildList(const char* aStartingAt,
   const PrefName& parent = GetPrefName(aStartingAt);
   size_t parentLen = parent.Length();
   for (auto iter = gHashTable->Iter(); !iter.Done(); iter.Next()) {
-    Pref* pref = static_cast<PrefEntry*>(iter.Get())->mPref;
-    if (strncmp(pref->Name(), parent.get(), parentLen) == 0) {
-      prefArray.AppendElement(pref->Name());
+    if (strncmp(iter.Key(), parent.get(), parentLen) == 0) {
+      prefArray.AppendElement(iter.Key());
     }
   }
 
@@ -2685,7 +2639,7 @@ PreferenceServiceReporter::CollectReports(
   if (gHashTable) {
     sizes.mHashTable += gHashTable->ShallowSizeOfIncludingThis(mallocSizeOf);
     for (auto iter = gHashTable->Iter(); !iter.Done(); iter.Next()) {
-      Pref* pref = static_cast<PrefEntry*>(iter.Get())->mPref;
+      Pref* pref = iter.Data();
       pref->AddSizeOfIncludingThis(mallocSizeOf, sizes);
     }
   }
@@ -2878,8 +2832,7 @@ Preferences::GetInstanceForService()
   sPreferences = new Preferences();
 
   MOZ_ASSERT(!gHashTable);
-  gHashTable = new PLDHashTable(
-    &pref_HashTableOps, sizeof(PrefEntry), PREF_HASHTABLE_INITIAL_LENGTH);
+  gHashTable = new PrefsTable(PREF_HASHTABLE_INITIAL_LENGTH);
 
   gTelemetryLoadData =
     new nsDataHashtable<nsCStringHashKey, TelemetryLoadData>();
@@ -3134,7 +3087,7 @@ Preferences::ResetPrefs()
 {
   ENSURE_PARENT_PROCESS("Preferences::ResetPrefs", "all prefs");
 
-  gHashTable->ClearAndPrepareForLength(PREF_HASHTABLE_INITIAL_LENGTH);
+  gHashTable->Clear();
   gPrefNameArena.Clear();
 
   return InitInitialObjects().isOk() ? NS_OK : NS_ERROR_FAILURE;
@@ -3149,10 +3102,10 @@ Preferences::ResetUserPrefs()
 
   Vector<const char*> prefNames;
   for (auto iter = gHashTable->Iter(); !iter.Done(); iter.Next()) {
-    Pref* pref = static_cast<PrefEntry*>(iter.Get())->mPref;
+    Pref* pref = iter.Data();
 
     if (pref->HasUserValue()) {
-      if (!prefNames.append(pref->Name())) {
+      if (!prefNames.append(iter.Key())) {
         return NS_ERROR_OUT_OF_MEMORY;
       }
 
@@ -3226,12 +3179,7 @@ Preferences::SetPreference(const dom::Pref& aDomPref)
 
   const char* prefName = aDomPref.name().get();
 
-  auto entry = static_cast<PrefEntry*>(gHashTable->Add(prefName, fallible));
-  if (!entry) {
-    return;
-  }
-
-  Pref* pref = entry->mPref;
+  Pref* pref = gHashTable->LookupOrAdd(prefName);
 
   bool valueChanged = false;
   pref->FromDomPref(aDomPref, &valueChanged);
@@ -3247,7 +3195,7 @@ Preferences::SetPreference(const dom::Pref& aDomPref)
   //   needlessly, but that's ok because this case is rare.
   //
   if (!pref->HasDefaultValue() && !pref->HasUserValue()) {
-    gHashTable->RemoveEntry(entry);
+    gHashTable->Remove(prefName);
   }
 
   // Note: we don't have to worry about HandleDirty() because we are setting
@@ -3275,9 +3223,9 @@ Preferences::GetPreferences(InfallibleTArray<dom::Pref>* aDomPrefs)
   MOZ_ASSERT(XRE_IsParentProcess());
   MOZ_ASSERT(NS_IsMainThread());
 
-  aDomPrefs->SetCapacity(gHashTable->EntryCount());
+  aDomPrefs->SetCapacity(gHashTable->Count());
   for (auto iter = gHashTable->Iter(); !iter.Done(); iter.Next()) {
-    Pref* pref = static_cast<PrefEntry*>(iter.Get())->mPref;
+    Pref* pref = iter.Data();
 
     if (!pref->MustSendToContentProcesses()) {
       // The pref value hasn't changed since it was initialized at startup.
@@ -3288,7 +3236,7 @@ Preferences::GetPreferences(InfallibleTArray<dom::Pref>* aDomPrefs)
 
     if (pref->HasAdvisablySizedValues()) {
       dom::Pref* setting = aDomPrefs->AppendElement();
-      pref->ToDomPref(setting);
+      pref->ToDomPref(setting, iter.Key());
     }
   }
 }
@@ -4184,13 +4132,13 @@ Preferences::ClearUserInAnyProcess(const char* aPrefName)
 {
   NS_ENSURE_TRUE(InitStaticMembers(), NS_ERROR_NOT_AVAILABLE);
 
-  PrefEntry* entry = pref_HashTableLookupInner(aPrefName);
+  PrefsTable::LookupResult entry = pref_HashTableLookupInner(aPrefName);
   Pref* pref;
-  if (entry && (pref = entry->mPref) && pref->HasUserValue()) {
+  if (entry && (pref = entry.Data()) && pref->HasUserValue()) {
     pref->ClearUserValue();
 
     if (!pref->HasDefaultValue()) {
-      gHashTable->RemoveEntry(entry);
+      entry.Remove();
     }
 
     NotifyCallbacks(aPrefName);