Lazy Parse CSS

third_party/WebKit/Source/core/css/StyleSheetContents.cpp

 /*
  * (C) 1999-2003 Lars Knoll (knoll@kde.org)
  * Copyright (C) 2004, 2006, 2007, 2012 Apple Inc. All rights reserved.
  *
  * This library is free software; you can redistribute it and/or
  * modify it under the terms of the GNU Library General Public
  * License as published by the Free Software Foundation; either
  * version 2 of the License, or (at your option) any later version.
  *
  * This library is distributed in the hope that it will be useful,
@@ skipping 315 matching lines @@
     // TODO(horo): When we will use the original URL as the base URL, we can remove this check. crbug.com/553535
     if (cachedStyleSheet->response().wasFetchedViaServiceWorker()) {
         const KURL originalURL(cachedStyleSheet->response().originalURLViaServiceWorker());
         // |originalURL| is empty when the response is created in the SW.
         if (!originalURL.isEmpty() && !securityOrigin->canRequest(originalURL))
             isSameOriginRequest = false;
     }
 
     CSSStyleSheetResource::MIMETypeCheck mimeTypeCheck = isQuirksModeBehavior(m_parserContext.mode()) && isSameOriginRequest ? CSSStyleSheetResource::MIMETypeCheck::Lax : CSSStyleSheetResource::MIMETypeCheck::Strict;
     String sheetText = cachedStyleSheet->sheetText(mimeTypeCheck);
+    if (RuntimeEnabledFeatures::lazyParseCSSEnabled())
+        m_sheetText = sheetText;
 
     const ResourceResponse& response = cachedStyleSheet->response();
     m_sourceMapURL = response.httpHeaderField(HTTPNames::SourceMap);
     if (m_sourceMapURL.isEmpty()) {
         // Try to get deprecated header.
         m_sourceMapURL = response.httpHeaderField(HTTPNames::X_SourceMap);
     }
 
-    CSSParserContext context(parserContext(), UseCounter::getFrom(this));

[Timothy Loh, 2016/09/26 05:18:00]

Presumably there was some reason for this to be written this way -- it looks
like we're overriding the UseCounter on parserContext(). Could you try and work
out what's happening here? I worry that we'll end up failing to count a whole
lot of things.

[Charlie Harrison, 2016/09/26 22:14:45]

After looking through the code I think you're right.

I've attempted to solve this by persisting the StyleSheetContents in the
closure, and calling UseCounter::getFrom(stylesheet) when lazy parsing is
triggered. However, this is not performant for reasons I'm not sure about
(probably every Persistent<> triggers a lot of bookkeeping in Oilpan to add
another root to the graph).

The solution I ended up with is passing (unretained)
- The stylesheet's context
- The stylesheet's usecounter
This allows us to use this pattern when the closure is triggered.

-    CSSParser::parseSheet(context, this, sheetText);
+    // Note: pass the member context here, as lazy parsing requires retaining a
+    // reference to it.
+    CSSParser::parseSheet(parserContext(), this, sheetText, RuntimeEnabledFeatures::lazyParseCSSEnabled());
 }
 
 void StyleSheetContents::parseString(const String& sheetText)
 {
     parseStringAtPosition(sheetText, TextPosition::minimumPosition());
 }
 
 void StyleSheetContents::parseStringAtPosition(const String& sheetText, const TextPosition& startPosition)
 {
     CSSParserContext context(parserContext(), UseCounter::getFrom(this));
@@ skipping 111 matching lines @@
     StyleSheetContents* root = rootStyleSheet();
     return root->clientSingleOwnerDocument();
 }
 
 static bool childRulesHaveFailedOrCanceledSubresources(const HeapVector<Member<StyleRuleBase>>& rules)
 {
     for (unsigned i = 0; i < rules.size(); ++i) {
         const StyleRuleBase* rule = rules[i].get();
         switch (rule->type()) {
         case StyleRuleBase::Style:
-            if (toStyleRule(rule)->properties().hasFailedOrCanceledSubresources())
+            if (toStyleRule(rule)->propertiesHaveFailedOrCanceledSubresources())
                 return true;
             break;
         case StyleRuleBase::FontFace:
             if (toStyleRuleFontFace(rule)->properties().hasFailedOrCanceledSubresources())
                 return true;
             break;
         case StyleRuleBase::Media:
             if (childRulesHaveFailedOrCanceledSubresources(toStyleRuleMedia(rule)->childRules()))
                 return true;
             break;
@@ skipping 176 matching lines @@
     visitor->trace(m_importRules);
     visitor->trace(m_namespaceRules);
     visitor->trace(m_childRules);
     visitor->trace(m_loadingClients);
     visitor->trace(m_completedClients);
     visitor->trace(m_ruleSet);
     visitor->trace(m_referencedFromResource);
 }
 
 } // namespace blink