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Rules and their declarations are a single object as far as the CC is concerned. They have a single nsCycleCollectionISupports and they are represented by a single node in the CC graph. That single object has two nsWrapperCache instances in it that point to different JS objects, and we need to make sure that the ordering of the unlink operations for those nsWrapperCache instances is handled correctly. Differential Revision: https://phabricator.services.mozilla.com/D38326 --HG-- extra : moz-landing-system : lando
107 lines
3.4 KiB
C++
107 lines
3.4 KiB
C++
/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
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/* vim: set ts=8 sts=2 et sw=2 tw=80: */
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/* This Source Code Form is subject to the terms of the Mozilla Public
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* License, v. 2.0. If a copy of the MPL was not distributed with this
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* file, You can obtain one at http://mozilla.org/MPL/2.0/. */
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/* base class for all rule types in a CSS style sheet */
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#include "Rule.h"
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#include "mozilla/css/GroupRule.h"
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#include "mozilla/dom/DocumentOrShadowRoot.h"
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#include "nsCCUncollectableMarker.h"
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#include "mozilla/dom/Document.h"
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#include "nsWrapperCacheInlines.h"
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using namespace mozilla;
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using namespace mozilla::dom;
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namespace mozilla {
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namespace css {
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NS_IMPL_CYCLE_COLLECTING_ADDREF(Rule)
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NS_IMPL_CYCLE_COLLECTING_RELEASE(Rule)
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NS_INTERFACE_MAP_BEGIN_CYCLE_COLLECTION(Rule)
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NS_WRAPPERCACHE_INTERFACE_MAP_ENTRY
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NS_INTERFACE_MAP_ENTRY(nsISupports)
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NS_INTERFACE_MAP_END
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NS_IMPL_CYCLE_COLLECTION_WRAPPERCACHE_0(Rule)
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bool Rule::IsCCLeaf() const { return !PreservingWrapper(); }
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bool Rule::IsKnownLive() const {
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if (HasKnownLiveWrapper()) {
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return true;
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}
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StyleSheet* sheet = GetStyleSheet();
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if (!sheet) {
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return false;
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}
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if (!sheet->IsKeptAliveByDocument()) {
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return false;
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}
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return nsCCUncollectableMarker::InGeneration(
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GetComposedDoc()->GetMarkedCCGeneration());
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}
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void Rule::UnlinkDeclarationWrapper(nsWrapperCache& aDecl) {
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// We have to be a bit careful here. We have two separate nsWrapperCache
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// instances, aDecl and this, that both correspond to the same CC participant:
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// this. If we just used ReleaseWrapper() on one of them, that would
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// unpreserve that one wrapper, then trace us with a tracer that clears JS
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// things, and we would clear the wrapper on the cache that has not
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// unpreserved the wrapper yet. That would violate the invariant that the
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// cache keeps caching the wrapper until the wrapper dies.
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//
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// So we reimplement a modified version of nsWrapperCache::ReleaseWrapper here
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// that unpreserves both wrappers before doing any clearing.
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bool needDrop = PreservingWrapper() || aDecl.PreservingWrapper();
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SetPreservingWrapper(false);
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aDecl.SetPreservingWrapper(false);
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if (needDrop) {
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DropJSObjects(this);
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}
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}
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NS_IMPL_CYCLE_COLLECTION_CAN_SKIP_BEGIN(Rule)
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return tmp->IsCCLeaf() || tmp->IsKnownLive();
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NS_IMPL_CYCLE_COLLECTION_CAN_SKIP_END
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NS_IMPL_CYCLE_COLLECTION_CAN_SKIP_IN_CC_BEGIN(Rule)
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// Please see documentation for nsCycleCollectionParticipant::CanSkip* for why
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// we need to check HasNothingToTrace here but not in the other two CanSkip
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// methods.
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return tmp->IsCCLeaf() || (tmp->IsKnownLive() && tmp->HasNothingToTrace(tmp));
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NS_IMPL_CYCLE_COLLECTION_CAN_SKIP_IN_CC_END
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NS_IMPL_CYCLE_COLLECTION_CAN_SKIP_THIS_BEGIN(Rule)
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return tmp->IsCCLeaf() || tmp->IsKnownLive();
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NS_IMPL_CYCLE_COLLECTION_CAN_SKIP_THIS_END
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/* virtual */
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void Rule::DropSheetReference() { mSheet = nullptr; }
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void Rule::SetCssText(const nsAString& aCssText) {
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// We used to throw for some rule types, but not all. Specifically, we did
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// not throw for StyleRule. Let's just always not throw.
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}
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Rule* Rule::GetParentRule() const { return mParentRule; }
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bool Rule::IsReadOnly() const {
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MOZ_ASSERT(!mSheet || !mParentRule ||
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mSheet->IsReadOnly() == mParentRule->IsReadOnly(),
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"a parent rule should be read only iff the owning sheet is "
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"read only");
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return mSheet && mSheet->IsReadOnly();
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}
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} // namespace css
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} // namespace mozilla
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