Make the HTMLDocumentParser yield more aggressively

Source/core/html/parser/HTMLDocumentParser.cpp

Index: Source/core/html/parser/HTMLDocumentParser.cpp
diff --git a/Source/core/html/parser/HTMLDocumentParser.cpp b/Source/core/html/parser/HTMLDocumentParser.cpp
index aa791dbb3611a8a93b61c4a6a18d0ff88facc558..76797259f2cdfbb8779186f2d021e270ef4f5c13 100644
--- a/Source/core/html/parser/HTMLDocumentParser.cpp
+++ b/Source/core/html/parser/HTMLDocumentParser.cpp
@@ -325,23 +325,11 @@ void HTMLDocumentParser::didReceiveParsedChunkFromBackgroundParser(PassOwnPtr<Pa
 {
     TRACE_EVENT0("webkit", "HTMLDocumentParser::didReceiveParsedChunkFromBackgroundParser");
 
-    // alert(), runModalDialog, and the JavaScript Debugger all run nested event loops
-    // which can cause this method to be re-entered. We detect re-entry using
-    // hasActiveParser(), save the chunk as a speculation, and return.
-    if (isWaitingForScripts() || !m_speculations.isEmpty() || document()->activeParserCount() > 0) {
-        m_preloader->takeAndPreload(chunk->preloads);
-        m_speculations.append(chunk);
-        return;
-    }
-
-    // processParsedChunkFromBackgroundParser can cause this parser to be detached from the Document,
-    // but we need to ensure it isn't deleted yet.
-    RefPtr<HTMLDocumentParser> protect(this);
-
-    ASSERT(m_speculations.isEmpty());
-    chunk->preloads.clear(); // We don't need to preload because we're going to parse immediately.
+    m_preloader->takeAndPreload(chunk->preloads);
     m_speculations.append(chunk);

[abarth-chromium, 2014/04/29 18:29:00]

Should we rename m_speculations?  I'm not sure that's exactly the right name.

IMHO, we'll eventually want to integrate this logic with a global scheduler that
understands whether we're trying to rAF every 16ms or we're in a bulk processing
phase.

-    pumpPendingSpeculations();
+    // If we're already paused waiting for scripts, no need to schedule a resume.
+    if (!isWaitingForScripts())
+        m_parserScheduler->scheduleForResume();
 }
 
 void HTMLDocumentParser::didReceiveEncodingDataFromBackgroundParser(const DocumentEncodingData& data)
@@ -436,6 +424,11 @@ void HTMLDocumentParser::processParsedChunkFromBackgroundParser(PassOwnPtr<Parse
             break;
     }
 
+    // FIXME: Currently this always consumes an entire chunk at once thus the time
+    // between deadline checks is controlled by BackgroundHTMLParser.cpp's pendingTokenLimit.
+    // We could make this code able to yield within a chunk, which would separate the
+    // question of how much the tokenizer should batch into a chunk from how long
+    // the main thread should spend treebuilding before yielding.
     for (Vector<CompactHTMLToken>::const_iterator it = tokens->begin(); it != tokens->end(); ++it) {
         ASSERT(!isWaitingForScripts());
 
@@ -483,7 +476,8 @@ void HTMLDocumentParser::processParsedChunkFromBackgroundParser(PassOwnPtr<Parse
 void HTMLDocumentParser::pumpPendingSpeculations()
 {
     // FIXME: Share this constant with the parser scheduler.
-    const double parserTimeLimit = 0.500;
+    // FIXME: This could be much larger during intial load where it may be OK to hog the main thread.
+    const double parserTimeLimit = 0.008;

[abarth-chromium, 2014/04/29 18:29:00]

Again, this seems like a value the scheduler might want to tune dynamically.

 
     // ASSERT that this object is both attached to the Document and protected.
     ASSERT(refCount() >= 2);