#375: M1351303

dom/base/Element.cpp

@@ -1197,10 +1197,10 @@ Element::SetAttribute(const nsAString& aName,
     if (IsHTMLElement() && IsInHTMLDocument()) {
       nsAutoString lower;
       nsContentUtils::ASCIIToLower(aName, lower);
-      nameAtom = do_GetAtom(lower);
+      nameAtom = NS_AtomizeMainThread(lower);
     }
     else {
-      nameAtom = do_GetAtom(aName);
+      nameAtom = NS_AtomizeMainThread(aName);
     }
     if (!nameAtom) {
       aError.Throw(NS_ERROR_OUT_OF_MEMORY);
@@ -1282,7 +1282,7 @@ Element::GetAttributeNS(const nsAString& aNamespaceURI,
     return;
   }
 
-  nsCOMPtr<nsIAtom> name = do_GetAtom(aLocalName);
+  nsCOMPtr<nsIAtom> name = NS_AtomizeMainThread(aLocalName);
   bool hasAttr = GetAttr(nsid, name, aReturn);
   if (!hasAttr) {
     SetDOMStringToNull(aReturn);
@@ -1314,7 +1314,7 @@ Element::RemoveAttributeNS(const nsAString& aNamespaceURI,
                            const nsAString& aLocalName,
                            ErrorResult& aError)
 {
-  nsCOMPtr<nsIAtom> name = do_GetAtom(aLocalName);
+  nsCOMPtr<nsIAtom> name = NS_AtomizeMainThread(aLocalName);
   int32_t nsid =
     nsContentUtils::NameSpaceManager()->GetNameSpaceID(aNamespaceURI);
 
@@ -1400,7 +1400,7 @@ Element::HasAttributeNS(const nsAString& aNamespaceURI,
     return false;
   }
 
-  nsCOMPtr<nsIAtom> name = do_GetAtom(aLocalName);
+  nsCOMPtr<nsIAtom> name = NS_AtomizeMainThread(aLocalName);
   return HasAttr(nsid, name);
 }
 

dom/base/nsAttrValue.cpp

@@ -735,7 +735,7 @@ nsAttrValue::GetAsAtom() const
 {
   switch (Type()) {
     case eString:
-      return do_GetAtom(GetStringValue());
+      return NS_AtomizeMainThread(GetStringValue());
 
     case eAtom:
       {
@@ -747,7 +747,7 @@ nsAttrValue::GetAsAtom() const
       {
         nsAutoString val;
         ToString(val);
-        return do_GetAtom(val);
+        return NS_AtomizeMainThread(val);
       }
   }
 }
@@ -1260,7 +1260,7 @@ nsAttrValue::ParseAtomArray(const nsAString& aValue)
     ++iter;
   } while (iter != end && !nsContentUtils::IsHTMLWhitespace(*iter));
 
-  nsCOMPtr<nsIAtom> classAtom = do_GetAtom(Substring(start, iter));
+  nsCOMPtr<nsIAtom> classAtom = NS_AtomizeMainThread(Substring(start, iter));
   if (!classAtom) {
     Reset();
     return;
@@ -1301,7 +1301,7 @@ nsAttrValue::ParseAtomArray(const nsAString& aValue)
       ++iter;
     } while (iter != end && !nsContentUtils::IsHTMLWhitespace(*iter));
 
-    classAtom = do_GetAtom(Substring(start, iter));
+    classAtom = NS_AtomizeMainThread(Substring(start, iter));
 
     if (!array->AppendElement(classAtom)) {
       Reset();
@@ -1718,7 +1718,7 @@ nsAttrValue::SetMiscAtomOrString(const nsAString* aValue)
                  "Empty string?");
     MiscContainer* cont = GetMiscContainer();
     if (len <= NS_ATTRVALUE_MAX_STRINGLENGTH_ATOM) {
-      nsCOMPtr<nsIAtom> atom = NS_NewAtom(*aValue);
+      nsCOMPtr<nsIAtom> atom = NS_AtomizeMainThread(*aValue);
       if (atom) {
         cont->mStringBits =
           reinterpret_cast<uintptr_t>(atom.forget().take()) | eAtomBase;

dom/base/nsContentUtils.cpp

@@ -2850,11 +2850,11 @@ nsContentUtils::SplitQName(const nsIContent* aNamespaceResolver,
     if (*aNamespace == kNameSpaceID_Unknown)
       return NS_ERROR_FAILURE;
 
-    *aLocalName = NS_NewAtom(Substring(colon + 1, end)).take();
+    *aLocalName = NS_AtomizeMainThread(Substring(colon + 1, end)).take();
   }
   else {
     *aNamespace = kNameSpaceID_None;
-    *aLocalName = NS_NewAtom(aQName).take();
+    *aLocalName = NS_AtomizeMainThread(aQName).take();
   }
   NS_ENSURE_TRUE(aLocalName, NS_ERROR_OUT_OF_MEMORY);
   return NS_OK;
@@ -2879,7 +2879,7 @@ nsContentUtils::GetNodeInfoFromQName(const nsAString& aNamespaceURI,
     const char16_t* end;
     qName.EndReading(end);
 
-    nsCOMPtr<nsIAtom> prefix = do_GetAtom(Substring(qName.get(), colon));
+    nsCOMPtr<nsIAtom> prefix = NS_AtomizeMainThread(Substring(qName.get(), colon));
 
     rv = aNodeInfoManager->GetNodeInfo(Substring(colon + 1, end), prefix,
                                        nsID, aNodeType, aNodeInfo);
@@ -2939,7 +2939,7 @@ nsContentUtils::SplitExpatName(const char16_t *aExpatName, nsIAtom **aPrefix,
     nameStart = (uriEnd + 1);
     if (nameEnd)  {
       const char16_t *prefixStart = nameEnd + 1;
-      *aPrefix = NS_NewAtom(Substring(prefixStart, pos)).take();
+      *aPrefix = NS_AtomizeMainThread(Substring(prefixStart, pos)).take();
     }
     else {
       nameEnd = pos;
@@ -2952,7 +2952,7 @@ nsContentUtils::SplitExpatName(const char16_t *aExpatName, nsIAtom **aPrefix,
     nameEnd = pos;
     *aPrefix = nullptr;
   }
-  *aLocalName = NS_NewAtom(Substring(nameStart, nameEnd)).take();
+  *aLocalName = NS_AtomizeMainThread(Substring(nameStart, nameEnd)).take();
 }
 
 // static
@@ -3708,7 +3708,7 @@ nsContentUtils::GetEventMessageAndAtom(const nsAString& aName,
   }
 
   *aEventMessage = eUnidentifiedEvent;
-  nsCOMPtr<nsIAtom> atom = do_GetAtom(NS_LITERAL_STRING("on") + aName);
+  nsCOMPtr<nsIAtom> atom = NS_AtomizeMainThread(NS_LITERAL_STRING("on") + aName);
   sUserDefinedEvents->AppendObject(atom);
   mapping.mAtom = atom;
   mapping.mMessage = eUnidentifiedEvent;

parser/html/nsHtml5TreeOperation.h

@@ -110,7 +110,7 @@ class nsHtml5TreeOperation {
       }
       nsAutoString str;
       aAtom->ToString(str);
-      return do_GetAtom(str);
+      return NS_AtomizeMainThread(str);
     }
 
     static nsresult AppendTextToTextNode(const char16_t* aBuffer,

xpcom/ds/nsAtomTable.cpp

@@ -298,6 +298,9 @@ static const PLDHashTableOps AtomTableOps = {
   AtomTableInitEntry
 };
 
+#define RECENTLY_USED_MAIN_THREAD_ATOM_CACHE_SIZE 31
+static nsIAtom*
+  sRecentlyUsedMainThreadAtoms[RECENTLY_USED_MAIN_THREAD_ATOM_CACHE_SIZE] = {};
 
 static inline
 void
@@ -651,6 +654,8 @@ NS_NewAtom(const char16_t* aUTF16String)
   return NS_NewAtom(nsDependentString(aUTF16String));
 }
 
+// Equivalent to current NS_Atomize and called by NS_AtomizeMainThread.
+// Left as such for legacy callers in our older 45-era codebase.
 already_AddRefed<nsIAtom>
 NS_NewAtom(const nsAString& aUTF16String)
 {
@@ -671,6 +676,43 @@ NS_NewAtom(const nsAString& aUTF16String)
   return atom.forget();
 }
 
+// From bug 1351303, modified for Mozilla 45.
+already_AddRefed<nsIAtom>
+NS_AtomizeMainThread(const nsAString& aUTF16String)
+{
+  MOZ_ASSERT(NS_IsMainThread());
+  nsCOMPtr<nsIAtom> retVal;
+  uint32_t hash;
+  AtomTableKey key(aUTF16String.Data(), aUTF16String.Length(), &hash);
+  uint32_t index = hash % RECENTLY_USED_MAIN_THREAD_ATOM_CACHE_SIZE;
+  nsIAtom* atom = sRecentlyUsedMainThreadAtoms[index];
+
+  if (atom) {
+    // This isn't ideal, but covers for the collision case, I guess.
+    // The atom names shouldn't be very long in any event.
+    uint32_t length = atom->GetLength();
+    if (length == key.mLength &&
+        (memcmp(atom->GetUTF16String(),
+                key.mUTF16String, length * sizeof(char16_t)) == 0)) {
+      retVal = atom;
+      return retVal.forget();
+    }
+  }
+
+  // Inline relevant parts of GetAtomHashEntry.
+  AtomTableEntry* he = static_cast<AtomTableEntry*>(gAtomTable->Add(&key));
+  if (he->mAtom) {
+    retVal = he->mAtom;
+  } else {
+    RefPtr<AtomImpl> atom = new AtomImpl(aUTF16String, hash);
+    he->mAtom = atom;
+    retVal = he->mAtom; // XXX?
+  }
+
+  sRecentlyUsedMainThreadAtoms[index] = retVal;
+  return retVal.forget();
+}
+
 nsIAtom*
 NS_NewPermanentAtom(const nsAString& aUTF16String)
 {

xpcom/ds/nsIAtom.idl

@@ -127,6 +127,11 @@ extern nsIAtom* NS_NewPermanentAtom(const nsAString& aUTF16String);
 inline already_AddRefed<nsIAtom> do_GetAtom(const nsAString& aUTF16String)
     { return NS_NewAtom(aUTF16String); }
 
+/**
+ * An optimized version of the method above for the main thread (bug 1351303).
+ */
+extern already_AddRefed<nsIAtom> NS_AtomizeMainThread(const nsAString& aUTF16String);
+
 /**
  * Return a count of the total number of atoms currently
  * alive in the system.