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,
 * PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR
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#include "config.h"
#include "core/html/parser/BackgroundHTMLParser.h"

#include "core/HTMLNames.h"
#include "core/html/parser/HTMLDocumentParser.h"
#include "core/html/parser/TextResourceDecoder.h"
#include "core/html/parser/XSSAuditor.h"
#include "platform/Task.h"
#include "platform/ThreadSafeFunctional.h"
#include "public/platform/Platform.h"
#include "public/platform/WebScheduler.h"
#include "wtf/text/TextPosition.h"

namespace blink {

// 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 tokens arbitrarily to 10,000.
// Our maximal memory spent speculating will be approximately:
// (defaultOutstandingTokenLimit + defaultPendingTokenLimit) *
//     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 (10000 + 1000) * 28 bytes = ~308kb of memory.
// These numbers have not been tuned.
static const size_t defaultOutstandingTokenLimit = 10000;

// 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 defaultPendingTokenLimit = 1000;

using namespace HTMLNames;

#if ENABLE(ASSERT)

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

void BackgroundHTMLParser::start(PassRefPtr<WeakReference<BackgroundHTMLParser>> reference, PassOwnPtr<Configuration> config, WebScheduler* scheduler)
{
    new BackgroundHTMLParser(reference, config, scheduler);
    // Caller must free by calling stop().
}

BackgroundHTMLParser::Configuration::Configuration()
    : outstandingTokenLimit(defaultOutstandingTokenLimit)
    , pendingTokenLimit(defaultPendingTokenLimit)
{
}

BackgroundHTMLParser::BackgroundHTMLParser(PassRefPtr<WeakReference<BackgroundHTMLParser>> reference, PassOwnPtr<Configuration> config, WebScheduler* scheduler)
    : m_weakFactory(reference, this)
    , m_token(adoptPtr(new HTMLToken))
    , m_tokenizer(HTMLTokenizer::create(config->options))
    , m_treeBuilderSimulator(config->options)
    , m_options(config->options)
    , m_outstandingTokenLimit(config->outstandingTokenLimit)
    , m_parser(config->parser)
    , m_pendingTokens(adoptPtr(new CompactHTMLTokenStream))
    , m_pendingTokenLimit(config->pendingTokenLimit)
    , m_xssAuditor(config->xssAuditor.release())
    , m_preloadScanner(config->preloadScanner.release())
    , m_decoder(config->decoder.release())
    , m_scheduler(scheduler)
    , m_startingScript(false)
{
    ASSERT(m_outstandingTokenLimit > 0);
    ASSERT(m_pendingTokenLimit > 0);
    ASSERT(m_outstandingTokenLimit >= m_pendingTokenLimit);
}

BackgroundHTMLParser::~BackgroundHTMLParser()
{
}

void BackgroundHTMLParser::appendRawBytesFromParserThread(const char* data, int dataLength)
{
    ASSERT(m_decoder);
    updateDocument(m_decoder->decode(data, dataLength));
}

void BackgroundHTMLParser::appendRawBytesFromMainThread(PassOwnPtr<Vector<char>> buffer)
{
    ASSERT(m_decoder);
    updateDocument(m_decoder->decode(buffer->data(), buffer->size()));
}

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

void BackgroundHTMLParser::setDecoder(PassOwnPtr<TextResourceDecoder> decoder)
{
    ASSERT(decoder);
    m_decoder = decoder;
}

void BackgroundHTMLParser::flush()
{
    ASSERT(m_decoder);
    updateDocument(m_decoder->flush());
}

void BackgroundHTMLParser::updateDocument(const String& decodedData)
{
    DocumentEncodingData encodingData(*m_decoder.get());

    if (encodingData != m_lastSeenEncodingData) {
        m_lastSeenEncodingData = encodingData;

        m_xssAuditor->setEncoding(encodingData.encoding());
        m_scheduler->loadingTaskRunner()->postTask(
            FROM_HERE,
            threadSafeBind(&HTMLDocumentParser::didReceiveEncodingDataFromBackgroundParser, AllowCrossThreadAccess(m_parser), encodingData));
    }

    if (decodedData.isEmpty())
        return;

    appendDecodedBytes(decodedData);
}

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);
    m_startingScript = false;
    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()
{
    HTMLTreeBuilderSimulator::SimulatedToken simulatedToken = HTMLTreeBuilderSimulator::OtherToken;

    // No need to start speculating until the main thread has almost caught up.
    if (m_input.totalCheckpointTokenCount() > m_outstandingTokenLimit)
        return;

    while (true) {
        if (m_xssAuditor->isEnabled())
            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;
        }

        if (m_xssAuditor->isEnabled())
            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(), position);

            m_preloadScanner->scan(token, m_input.current(), m_pendingPreloads);
            simulatedToken = m_treeBuilderSimulator.simulate(token, m_tokenizer.get());

            // Break chunks before a script tag is inserted and flag the chunk as starting a script
            // so the main parser can decide if it should yield before processing the chunk.
            if (simulatedToken == HTMLTreeBuilderSimulator::ScriptStart) {
                sendTokensToMainThread();
                m_startingScript = true;
            }

            m_pendingTokens->append(token);
        }

        m_token->clear();

        if (simulatedToken == HTMLTreeBuilderSimulator::ScriptEnd || m_pendingTokens->size() >= m_pendingTokenLimit) {
            sendTokensToMainThread();
            // If we're far ahead of the main thread, yield for a bit to avoid consuming too much memory.
            if (m_input.totalCheckpointTokenCount() > m_outstandingTokenLimit)
                break;
        }
    }
}

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

#if ENABLE(ASSERT)
    checkThatTokensAreSafeToSendToAnotherThread(m_pendingTokens.get());
    checkThatPreloadsAreSafeToSendToAnotherThread(m_pendingPreloads);
    checkThatXSSInfosAreSafeToSendToAnotherThread(m_pendingXSSInfos);
#endif

    OwnPtr<HTMLDocumentParser::ParsedChunk> chunk = adoptPtr(new HTMLDocumentParser::ParsedChunk);
    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(m_pendingTokens->size());
    chunk->preloadScannerCheckpoint = m_preloadScanner->createCheckpoint();
    chunk->tokens = m_pendingTokens.release();
    chunk->startingScript = m_startingScript;
    m_startingScript = false;

    m_scheduler->loadingTaskRunner()->postTask(
        FROM_HERE,
        new Task(threadSafeBind(&HTMLDocumentParser::didReceiveParsedChunkFromBackgroundParser, AllowCrossThreadAccess(m_parser), chunk.release())));

    m_pendingTokens = adoptPtr(new CompactHTMLTokenStream);
}

}