third_party/WebKit/Source/core/html/parser/HTMLParserScheduler.cpp

/*
 * Copyright (C) 2010 Google, Inc. All Rights Reserved.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 * 1. Redistributions of source code must retain the above copyright
 *    notice, this list of conditions and the following disclaimer.
 * 2. Redistributions in binary form must reproduce the above copyright
 *    notice, this list of conditions and the following disclaimer in the
 *    documentation and/or other materials provided with the distribution.
 *
 * THIS SOFTWARE IS PROVIDED BY APPLE INC. ``AS IS'' AND ANY
 * EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
 * PURPOSE ARE DISCLAIMED.  IN NO EVENT SHALL APPLE INC. OR
 * CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL,
 * EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO,
 * PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR
 * PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY
 * OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
 * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
 * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 */

#include "core/html/parser/HTMLParserScheduler.h"

#include "core/dom/Document.h"
#include "core/frame/FrameView.h"
#include "core/html/parser/HTMLDocumentParser.h"
#include "public/platform/Platform.h"
#include "public/platform/WebScheduler.h"
#include "public/platform/WebThread.h"
#include "wtf/CurrentTime.h"
#include "wtf/PtrUtil.h"

namespace blink {

PumpSession::PumpSession(unsigned& nestingLevel)
    : NestingLevelIncrementer(nestingLevel) {}

PumpSession::~PumpSession() {}

SpeculationsPumpSession::SpeculationsPumpSession(unsigned& nestingLevel)
    : NestingLevelIncrementer(nestingLevel),
      m_startTime(currentTime()),
      m_processedElementTokens(0) {}

SpeculationsPumpSession::~SpeculationsPumpSession() {}

inline double SpeculationsPumpSession::elapsedTime() const {
  return currentTime() - m_startTime;
}

void SpeculationsPumpSession::addedElementTokens(size_t count) {
  m_processedElementTokens += count;
}

HTMLParserScheduler::HTMLParserScheduler(HTMLDocumentParser* parser,
                                         WebTaskRunner* loadingTaskRunner)
    : m_parser(parser),
      m_loadingTaskRunner(loadingTaskRunner->clone()),
      m_cancellableContinueParse(CancellableTaskFactory::create(
          this,
          &HTMLParserScheduler::continueParsing)),
      m_isSuspendedWithActiveTimer(false) {}

HTMLParserScheduler::~HTMLParserScheduler() {}

DEFINE_TRACE(HTMLParserScheduler) {
  visitor->trace(m_parser);
}

void HTMLParserScheduler::scheduleForResume() {
  ASSERT(!m_isSuspendedWithActiveTimer);
  m_loadingTaskRunner->postTask(BLINK_FROM_HERE,
                                m_cancellableContinueParse->cancelAndCreate());
}

void HTMLParserScheduler::suspend() {
  ASSERT(!m_isSuspendedWithActiveTimer);
  if (!m_cancellableContinueParse->isPending())
    return;
  m_isSuspendedWithActiveTimer = true;
  m_cancellableContinueParse->cancel();
}

void HTMLParserScheduler::resume() {
  ASSERT(!m_cancellableContinueParse->isPending());
  if (!m_isSuspendedWithActiveTimer)
    return;
  m_isSuspendedWithActiveTimer = false;

  m_loadingTaskRunner->postTask(BLINK_FROM_HERE,
                                m_cancellableContinueParse->cancelAndCreate());
}

void HTMLParserScheduler::detach() {
  m_cancellableContinueParse->cancel();
  m_isSuspendedWithActiveTimer = false;
}

inline bool HTMLParserScheduler::shouldYield(
    const SpeculationsPumpSession& session,
    bool startingScript) const {
  if (Platform::current()
          ->currentThread()
          ->scheduler()
          ->shouldYieldForHighPriorityWork())
    return true;

  const double parserTimeLimit = 0.5;
  if (session.elapsedTime() > parserTimeLimit)
    return true;

  // Yield if a lot of DOM work has been done in this session and a script tag
  // is about to be parsed. This significantly improves render performance for
  // documents that place their scripts at the bottom of the page. Yielding too
  // often significantly slows down the parsing so a balance needs to be struck
  // to only yield when enough changes have happened to make it worthwhile.
  // Emperical testing shows that anything > ~40 and < ~200 gives all of the
  // benefit without impacting parser performance, only adding a few yields per
  // page but at just the right times.
  const size_t sufficientWork = 50;
  if (startingScript && session.processedElementTokens() > sufficientWork)
    return true;

  return false;
}

bool HTMLParserScheduler::yieldIfNeeded(const SpeculationsPumpSession& session,
                                        bool startingScript) {
  if (shouldYield(session, startingScript)) {
    scheduleForResume();
    return true;
  }

  return false;
}

void HTMLParserScheduler::forceResumeAfterYield() {
  ASSERT(!m_cancellableContinueParse->isPending());
  m_isSuspendedWithActiveTimer = true;
}

void HTMLParserScheduler::continueParsing() {
  m_parser->resumeParsingAfterYield();
}

}  // namespace blink