1 files changed, 81 insertions, 0 deletions
diff --git a/layout/style/IncrementalClearCOMRuleArray.cpp b/layout/style/IncrementalClearCOMRuleArray.cpp
new file mode 100644
index 000000000..92cdced22
--- /dev/null
+++ b/layout/style/IncrementalClearCOMRuleArray.cpp
@@ -0,0 +1,81 @@
+/* -*- 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 "mozilla/IncrementalClearCOMRuleArray.h"
+
+#include <algorithm> // For std::min
+#include "nsCycleCollector.h"
+#include "mozilla/DeferredFinalize.h"
+#include "nsTArray.h"
+#include "nsCCUncollectableMarker.h"
+
+using namespace mozilla;
+
+typedef nsCOMArray<css::Rule> RuleArray;
+typedef nsTArray<RuleArray> RuleArrayArray;
+
+
+// These methods are based on those in DeferredFinalizerImpl.
+
+static void*
+AppendRulesArrayPointer(void* aData, void* aObject)
+{
+  RuleArrayArray* rulesArray = static_cast<RuleArrayArray*>(aData);
+  RuleArray* oldRules = static_cast<RuleArray*>(aObject);
+
+  if (!rulesArray) {
+    rulesArray = new RuleArrayArray();
+  }
+
+  RuleArray* newRules = rulesArray->AppendElement();
+  newRules->SwapElements(*oldRules);
+
+  return rulesArray;
+}
+
+// Remove up to |aSliceBudget| css::Rules from the arrays, starting at
+// the end of the last array.
+static bool
+DeferredFinalizeRulesArray(uint32_t aSliceBudget, void* aData)
+{
+  MOZ_ASSERT(aSliceBudget > 0, "nonsensical/useless call with aSliceBudget == 0");
+  RuleArrayArray* rulesArray = static_cast<RuleArrayArray*>(aData);
+
+  size_t newOuterLen = rulesArray->Length();
+
+  while (aSliceBudget > 0 && newOuterLen > 0) {
+    RuleArray& lastArray = rulesArray->ElementAt(newOuterLen - 1);
+    uint32_t innerLen = lastArray.Length();
+    uint32_t currSlice = std::min(innerLen, aSliceBudget);
+    uint32_t newInnerLen = innerLen - currSlice;
+    lastArray.TruncateLength(newInnerLen);
+    aSliceBudget -= currSlice;
+    if (newInnerLen == 0) {
+      newOuterLen -= 1;
+    }
+  }
+
+  rulesArray->TruncateLength(newOuterLen);
+
+  if (newOuterLen == 0) {
+    delete rulesArray;
+    return true;
+  }
+  return false;
+}
+
+void
+IncrementalClearCOMRuleArray::Clear()
+{
+  // Destroy the array incrementally if it is long and we
+  // haven't started shutting down.
+  if (Length() > 10 && nsCCUncollectableMarker::sGeneration) {
+    DeferredFinalize(AppendRulesArrayPointer, DeferredFinalizeRulesArray, this);
+  } else {
+    nsCOMArray<css::Rule>::Clear();
+  }
+  MOZ_ASSERT(Length() == 0);
+}