KeyAtomStringCacheInlines.h

/*
 * Copyright (C) 2023 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
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 * 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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 * INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
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 */

#pragma once

#include "Identifier.h"
#include "JSString.h"
#include "KeyAtomStringCache.h"
#include "Options.h"
#include "SmallStrings.h"
#include "VM.h"
#include <atomic>
#include <stdlib.h>
#include <wtf/DataLog.h>

namespace JSC {

template<typename Buffer, typename Func>
ALWAYS_INLINE JSString* KeyAtomStringCache::make(VM& vm, Buffer& buffer, const Func& func)
{
    if (buffer.characters.empty())
        return jsEmptyString(vm);

    if (buffer.characters.size() == 1) {
        auto firstCharacter = buffer.characters[0];
        if (firstCharacter <= maxSingleCharacterString)
            return vm.smallStrings.singleCharacterString(firstCharacter);
    }

    ASSERT(buffer.characters.size() <= maxStringLengthForCache);
    auto& slot = m_cache[buffer.hash % capacity];
    // SNAPSHOT the slot once. The slot is shared by all lites under GIL-off
    // and ping-pongs between same-bucket atoms (e.g. "p8"/"p17" both hash to
    // bucket 357 of 512). We verify the snapshot and return the SAME
    // snapshot; re-reading the slot after verification can return a
    // different, also-valid atom and silently resolve the wrong property key
    // (UNGIL Race C; see KeyAtomStringCache.h).
    if (JSString* cached = slot.load(std::memory_order_acquire)) {
        if (auto* impl = cached->tryGetValueImpl()) {
            if (impl->hash() == buffer.hash && equal(impl, buffer.characters))
                return cached;
        }
    }

    JSString* result = func(vm, buffer);
    if (result) [[likely]]
        slot.store(result, std::memory_order_release);
    return result;
}

} // namespace JSC