Source/WebCore/style/MatchedDeclarationsCache.h

/*
 * Copyright (C) 2019 Apple 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. AND ITS CONTRIBUTORS ``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 ITS CONTRIBUTORS
 * BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
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 * SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
 * INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
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 */

#pragma once

#include "MatchResult.h"
#include "StyleComputedStyle.h"
#include "Timer.h"
#include <wtf/CanMakeWeakPtr.h>
#include <wtf/TZoneMalloc.h>
#include <wtf/WeakRef.h>

namespace WebCore {

namespace Style {

class Resolver;

class MatchedDeclarationsCache : public CanMakeWeakPtr<MatchedDeclarationsCache> {
    WTF_MAKE_TZONE_ALLOCATED(MatchedDeclarationsCache);
public:
    explicit MatchedDeclarationsCache(const Resolver&);
    ~MatchedDeclarationsCache();

    static bool isCacheable(const Element&, const Style::ComputedStyle&, const Style::ComputedStyle& parentStyle);
    static unsigned computeHash(const MatchResult&, const Style::CustomPropertyData& inheritedCustomProperties);

    struct Entry {
        RefPtr<const MatchResult> matchResult;
        std::unique_ptr<const Style::ComputedStyle> renderStyle;
        std::unique_ptr<const Style::ComputedStyle> parentRenderStyle;

        bool isUsableAfterHighPriorityProperties(const Style::ComputedStyle&) const;
    };

    struct Result {
        const Entry& entry;
        bool inheritedEqual;
    };

    std::optional<Result> find(unsigned hash, const MatchResult&, const Style::CustomPropertyData& inheritedCustomProperties, const Style::ComputedStyle&);
    void add(const Style::ComputedStyle&, const Style::ComputedStyle& parentStyle,  unsigned hash, const MatchResult&);
    void remove(unsigned hash);

    // Every N additions to the matched declaration cache trigger a sweep where entries holding
    // the last reference to a style declaration are garbage collected.
    void invalidate();
    void clearEntriesAffectedByViewportUnits();

    void NODELETE ref() const;
    void deref() const;

private:
    template<typename Callback>
    void removeAllMatching(const Callback& matches);

    void sweep();

    SingleThreadWeakRef<const Resolver> m_owner;
    HashMap<unsigned, Vector<Entry>, AlreadyHashed> m_entries;
    Timer m_sweepTimer;
    unsigned m_additionsSinceLastSweep { 0 };
};

}
}