Source/core/html/parser/BackgroundHTMLParser.cpp

/*
 * Copyright (C) 2013 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 GOOGLE 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 GOOGLE INC. OR
 * CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL,
 * EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO,
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#include "config.h"
#include "core/html/parser/BackgroundHTMLParser.h"

#include "core/html/parser/HTMLDocumentParser.h"
#include "core/html/parser/HTMLParserThread.h"
#include "core/html/parser/HTMLTokenizer.h"
#include "core/html/parser/XSSAuditor.h"
#include "wtf/MainThread.h"
#include "wtf/text/TextPosition.h"

namespace WebCore {

// On a network with high latency and high bandwidth, using a device
// with a fast CPU, we could end up speculatively tokenizing
// the whole document, well ahead of when the main-thread actually needs it.
// This is a waste of memory (and potentially time if the speculation fails).
// So we limit our outstanding speculations arbitrarily to 10.
// Our maximal memory spent speculating will be approximately:
// outstandingCheckpointLimit * pendingTokenLimit * sizeof(CompactToken)
// We use a separate low and high water mark to avoid constantly topping
// off the main thread's token buffer.
// At time of writing, this is 10 * 1000 * 28 bytes = appox 280kb of memory.
// These numbers have not been tuned.
static const size_t outstandingCheckpointLimit = 10;

// We limit our chucks to 1000 tokens, to make sure the main
// thread is never waiting on the parser thread for tokens.
// This was tuned in https://bugs.webkit.org/show_bug.cgi?id=110408.
static const size_t pendingTokenLimit = 1000;

using namespace HTMLNames;

#ifndef NDEBUG

static void checkThatTokensAreSafeToSendToAnotherThread(const CompactHTMLTokenStream* tokens)
{
    for (size_t i = 0; i < tokens->size(); ++i)
        ASSERT(tokens->at(i).isSafeToSendToAnotherThread());
}

static void checkThatPreloadsAreSafeToSendToAnotherThread(const PreloadRequestStream& preloads)
{
    for (size_t i = 0; i < preloads.size(); ++i)
        ASSERT(preloads[i]->isSafeToSendToAnotherThread());
}

static void checkThatXSSInfosAreSafeToSendToAnotherThread(const XSSInfoStream& infos)
{
    for (size_t i = 0; i < infos.size(); ++i)
        ASSERT(infos[i]->isSafeToSendToAnotherThread());
}

#endif

BackgroundHTMLParser::BackgroundHTMLParser(PassRefPtr<WeakReference<BackgroundHTMLParser> > reference, PassOwnPtr<Configuration> config)
    : m_weakFactory(reference, this)
    , m_token(adoptPtr(new HTMLToken))
    , m_tokenizer(HTMLTokenizer::create(config->options))
    , m_treeBuilderSimulator(config->options)
    , m_options(config->options)
    , m_parser(config->parser)
    , m_pendingTokens(adoptPtr(new CompactHTMLTokenStream))
    , m_xssAuditor(config->xssAuditor.release())
    , m_preloadScanner(config->preloadScanner.release())
{
}

void BackgroundHTMLParser::append(const String& input)
{
    ASSERT(!m_input.current().isClosed());
    m_input.append(input);
    pumpTokenizer();
}

void BackgroundHTMLParser::resumeFrom(PassOwnPtr<Checkpoint> checkpoint)
{
    m_parser = checkpoint->parser;
    m_token = checkpoint->token.release();
    m_tokenizer = checkpoint->tokenizer.release();
    m_treeBuilderSimulator.setState(checkpoint->treeBuilderState);
    m_input.rewindTo(checkpoint->inputCheckpoint, checkpoint->unparsedInput);
    m_preloadScanner->rewindTo(checkpoint->preloadScannerCheckpoint);
    pumpTokenizer();
}

void BackgroundHTMLParser::startedChunkWithCheckpoint(HTMLInputCheckpoint inputCheckpoint)
{
    // Note, we should not have to worry about the index being invalid
    // as messages from the main thread will be processed in FIFO order.
    m_input.invalidateCheckpointsBefore(inputCheckpoint);
    pumpTokenizer();
}

void BackgroundHTMLParser::finish()
{
    markEndOfFile();
    pumpTokenizer();
}

void BackgroundHTMLParser::stop()
{
    delete this;
}

void BackgroundHTMLParser::forcePlaintextForTextDocument()
{
    // This is only used by the TextDocumentParser (a subclass of HTMLDocumentParser)
    // to force us into the PLAINTEXT state w/o using a <plaintext> tag.
    // The TextDocumentParser uses a <pre> tag for historical/compatibility reasons.
    m_tokenizer->setState(HTMLTokenizer::PLAINTEXTState);
}

void BackgroundHTMLParser::markEndOfFile()
{
    ASSERT(!m_input.current().isClosed());
    m_input.append(String(&kEndOfFileMarker, 1));
    m_input.close();
}

void BackgroundHTMLParser::pumpTokenizer()
{
    // No need to start speculating until the main thread has almost caught up.
    if (m_input.outstandingCheckpointCount() > outstandingCheckpointLimit)
        return;

    while (true) {
        m_sourceTracker.start(m_input.current(), m_tokenizer.get(), *m_token);
        if (!m_tokenizer->nextToken(m_input.current(), *m_token)) {
            // We've reached the end of our current input.
            sendTokensToMainThread();
            break;
        }
        m_sourceTracker.end(m_input.current(), m_tokenizer.get(), *m_token);

        {
            TextPosition position = TextPosition(m_input.current().currentLine(), m_input.current().currentColumn());

            if (OwnPtr<XSSInfo> xssInfo = m_xssAuditor->filterToken(FilterTokenRequest(*m_token, m_sourceTracker, m_tokenizer->shouldAllowCDATA()))) {
                xssInfo->m_textPosition = position;
                m_pendingXSSInfos.append(xssInfo.release());
            }

            CompactHTMLToken token(m_token.get(), TextPosition(m_input.current().currentLine(), m_input.current().currentColumn()));

            m_preloadScanner->scan(token, m_input.current(), m_pendingPreloads);

            m_pendingTokens->append(token);
        }

        m_token->clear();

        if (!m_treeBuilderSimulator.simulate(m_pendingTokens->last(), m_tokenizer.get()) || m_pendingTokens->size() >= pendingTokenLimit) {
            sendTokensToMainThread();
            // If we're far ahead of the main thread, yield for a bit to avoid consuming too much memory.
            if (m_input.outstandingCheckpointCount() > outstandingCheckpointLimit)
                break;
        }
    }
}

void BackgroundHTMLParser::sendTokensToMainThread()
{
    if (m_pendingTokens->isEmpty())
        return;

#ifndef NDEBUG
    checkThatTokensAreSafeToSendToAnotherThread(m_pendingTokens.get());
    checkThatPreloadsAreSafeToSendToAnotherThread(m_pendingPreloads);
    checkThatXSSInfosAreSafeToSendToAnotherThread(m_pendingXSSInfos);
#endif

    OwnPtr<HTMLDocumentParser::ParsedChunk> chunk = adoptPtr(new HTMLDocumentParser::ParsedChunk);
    chunk->tokens = m_pendingTokens.release();
    chunk->preloads.swap(m_pendingPreloads);
    chunk->xssInfos.swap(m_pendingXSSInfos);
    chunk->tokenizerState = m_tokenizer->state();
    chunk->treeBuilderState = m_treeBuilderSimulator.state();
    chunk->inputCheckpoint = m_input.createCheckpoint();
    chunk->preloadScannerCheckpoint = m_preloadScanner->createCheckpoint();
    callOnMainThread(bind(&HTMLDocumentParser::didReceiveParsedChunkFromBackgroundParser, m_parser, chunk.release()));

    m_pendingTokens = adoptPtr(new CompactHTMLTokenStream);
}

}