Tracking filter mutation via SVGElementProxy

third_party/WebKit/Source/core/svg/SVGElementProxy.cpp

+// Copyright 2016 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#include "core/svg/SVGElementProxy.h"
+
+#include "core/dom/IdTargetObserver.h"
+#include "core/fetch/FetchInitiatorTypeNames.h"
+#include "core/fetch/FetchRequest.h"
+#include "core/fetch/ResourceFetcher.h"
+#include "core/svg/SVGElement.h"
+#include "core/svg/SVGFilterElement.h"
+#include "core/svg/SVGResourceClient.h"
+
+namespace blink {
+

[pdr., 2016/11/02 06:35:22]

Can you think of any race situations from using IdTargetObserver? For example,
are the notifications limited to certain document lifecycle phases that could be
asserted for safety?

[fs, 2016/11/02 15:49:22]

IIRC, Element::updateId is the primary hook (which is called by various DOM
mutation methods), so I guess one can't say there's any explicit lifecycle
dependencies? Implicitly though I guess we would expect
DocumentLifecycle::stateAllowsTreeMutations() to be true, so maybe that would be
something worth asserting? From the other side of things, I think we need <=
Compositing or so.

+class SVGElementProxy::IdObserver : public IdTargetObserver {

[pdr., 2016/11/02 06:35:22]

I didn't know about IdTargetObserver... Would this also be useful for other SVG
by-id tracking?

[fs, 2016/11/02 15:49:22]

Yes, I did get the same idea. I'll look in to it (if I remember.)

+ public:
+  IdObserver(TreeScope& treeScope, SVGElementProxy& proxy)
+      : IdTargetObserver(treeScope.idTargetObserverRegistry(), proxy.id()),
+        m_treeScope(&treeScope) {}
+
+  void addClient(SVGResourceClient* client) { m_clients.add(client); }
+  bool removeClient(SVGResourceClient* client) {
+    return m_clients.remove(client);
+  }
+
+  TreeScope* treeScope() const { return m_treeScope; }
+  void transferClients(IdObserver& observer) {
+    for (const auto& client : m_clients)
+      observer.m_clients.add(client.key, client.value);
+    m_clients.clear();
+  }
+
+  DEFINE_INLINE_VIRTUAL_TRACE() {
+    visitor->trace(m_clients);
+    visitor->trace(m_treeScope);
+    IdTargetObserver::trace(visitor);
+  }
+
+  void contentChanged() {
+    HeapVector<Member<SVGResourceClient>> clients;
+    copyToVector(m_clients, clients);
+    for (SVGResourceClient* client : clients)
+      client->resourceContentChanged();
+  }
+
+ private:
+  void idTargetChanged() override {
+    HeapVector<Member<SVGResourceClient>> clients;
+    copyToVector(m_clients, clients);
+    for (SVGResourceClient* client : clients)
+      client->resourceElementChanged();
+  }
+  HeapHashCountedSet<Member<SVGResourceClient>> m_clients;
+  Member<TreeScope> m_treeScope;
+};
+
+SVGElementProxy::SVGElementProxy(const AtomicString& id)
+    : m_id(id), m_isLocal(true) {}
+
+SVGElementProxy::SVGElementProxy(const String& url, const AtomicString& id)
+    : m_id(id), m_url(url), m_isLocal(false) {}
+
+SVGElementProxy::~SVGElementProxy() {}
+
+void SVGElementProxy::addClient(SVGResourceClient* client) {
+  // An empty id will never be a valid element reference.
+  if (m_id.isEmpty())
+    return;
+  if (m_document)
+    m_document->addClient(client);
+  TreeScope* clientScope = client->treeScope();
+  TreeScope* lookupScope =
+      clientScope ? treeScopeForLookup(*clientScope) : nullptr;
+  if (!lookupScope)
+    return;
+  // Ensure sure we have an observer registered for this tree scope.
+  auto& scopeObserver =
+      m_observers.add(lookupScope, nullptr).storedValue->value;
+  if (!scopeObserver)
+    scopeObserver = new IdObserver(*lookupScope, *this);
+
+  auto& observer = m_clients.add(client, nullptr).storedValue->value;
+  if (!observer)
+    observer = scopeObserver;
+
+  DCHECK(observer && scopeObserver);
+
+  // If the client moved to a different scope, we need to unregister the old
+  // observer and transfer any clients from it before replacing it. Thus any
+  // clients that remain to be removed will be transferred to the new observer,
+  // and hence removed from it instead.
+  if (observer != scopeObserver) {
+    observer->unregister();
+    observer->transferClients(*scopeObserver);
+    observer = scopeObserver;
+  }
+  observer->addClient(client);
+}
+
+void SVGElementProxy::removeClient(SVGResourceClient* client) {
+  // An empty id will never be a valid element reference.
+  if (m_id.isEmpty())
+    return;
+  if (m_document)
+    m_document->removeClient(client);
+  auto entry = m_clients.find(client);
+  if (entry == m_clients.end())
+    return;
+  IdObserver* observer = entry->value;
+  DCHECK(observer);
+  // If the client is not the last client in the scope, then no further action
+  // needs to be taken.
+  if (!observer->removeClient(client))
+    return;
+  // Unregister and drop the scope association, then drop the client.
+  observer->unregister();
+  m_observers.remove(observer->treeScope());
+  m_clients.remove(entry);
+}
+
+void SVGElementProxy::resolve(Document& document) {
+  if (m_isLocal || m_id.isEmpty() || m_url.isEmpty())
+    return;
+  FetchRequest request(ResourceRequest(m_url), FetchInitiatorTypeNames::css);
+  m_document = DocumentResource::fetchSVGDocument(request, document.fetcher());
+  m_url = String();
+}
+
+TreeScope* SVGElementProxy::treeScopeForLookup(TreeScope& treeScope) const {
+  if (m_isLocal)
+    return &treeScope;
+  if (!m_document)
+    return nullptr;
+  return m_document->document();
+}
+
+SVGElement* SVGElementProxy::findElement(TreeScope& treeScope) {
+  // An empty id will never be a valid element reference.
+  if (m_id.isEmpty())
+    return nullptr;
+  TreeScope* lookupScope = treeScopeForLookup(treeScope);
+  if (!lookupScope)
+    return nullptr;
+  if (Element* targetElement = lookupScope->getElementById(m_id)) {
+    if (isSVGFilterElement(*targetElement)) {
+      toSVGFilterElement(*targetElement).elementProxySet().add(*this);
+      return toSVGElement(targetElement);
+    }
+  }
+  return nullptr;
+}
+
+void SVGElementProxy::contentChanged(TreeScope& treeScope) {
+  if (auto observer = m_observers.get(&treeScope))
+    observer->contentChanged();
+}
+
+DEFINE_TRACE(SVGElementProxy) {
+  visitor->trace(m_clients);
+  visitor->trace(m_observers);
+  visitor->trace(m_document);
+}
+
+void SVGElementProxySet::add(SVGElementProxy& elementProxy) {
+  m_elementProxies.add(&elementProxy);
+}
+
+bool SVGElementProxySet::isEmpty() const {
+  return m_elementProxies.isEmpty();
+}
+
+void SVGElementProxySet::notifyContentChanged(TreeScope& treeScope) {
+  for (SVGElementProxy* proxy : m_elementProxies)
+    proxy->contentChanged(treeScope);
+}
+
+DEFINE_TRACE(SVGElementProxySet) {
+  visitor->trace(m_elementProxies);
+}
+
+}  // namespace blink