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/*
* Copyright (C) 2016-2021 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
* 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.
*/
#pragma once
#include "Heap.h"
namespace JSC {
class JSCell;
// Note that if all you're doing is calling LazyProperty::get(), it's completely safe to bitcast
// this LazyProperty<JSCell, JSCell>.
template<typename OwnerType, typename ElementType>
class LazyProperty {
public:
struct Initializer {
Initializer(OwnerType* owner, LazyProperty& property)
: vm(Heap::heap(owner)->vm())
, owner(owner)
, property(property)
{
}
void set(ElementType* value) const;
VM& vm;
OwnerType* owner;
LazyProperty& property;
};
private:
typedef ElementType* (*FuncType)(const Initializer&);
public:
LazyProperty()
{
}
// Tell the property to run the given callback next time someone tries to get the value
// using get(). The passed callback must be stateless. For example:
//
// property.initLater(
// [] (const LazyProperty<Foo, Bar>::Initializer& init) {
// init.set(...things...);
// });
//
// This method is always inlineable and should always compile to a store of a constant
// pointer no matter how complicated the callback is.
template<typename Func>
void initLater(const Func&);
// This lazily initializes the property. Note that this gracefully supports recursive calls.
// If this gets called while the property is being initialized, it will simply return null.
ElementType* get(const OwnerType* owner) const
{
ASSERT(!isCompilationThread());
return getInitializedOnMainThread(owner);
}
ElementType* getConcurrently() const
{
uintptr_t pointer = m_pointer;
if (pointer & lazyTag)
return nullptr;
return std::bit_cast<ElementType*>(pointer);
}
bool isInitialized() const { return !(m_pointer & lazyTag); }
ElementType* getInitializedOnMainThread(const OwnerType* owner) const
{
if (UNLIKELY(m_pointer & lazyTag)) {
ASSERT(!isCompilationThread());
FuncType func = *std::bit_cast<FuncType*>(m_pointer & ~(lazyTag | initializingTag));
return func(Initializer(const_cast<OwnerType*>(owner), *const_cast<LazyProperty*>(this)));
}
return std::bit_cast<ElementType*>(m_pointer);
}
void setMayBeNull(VM&, const OwnerType* owner, ElementType*);
void set(VM&, const OwnerType* owner, ElementType*);
template<typename Visitor> void visit(Visitor&);
void dump(PrintStream&) const;
private:
template<typename Func>
static ElementType* callFunc(const Initializer&);
static const uintptr_t lazyTag = 1;
static const uintptr_t initializingTag = 2;
uintptr_t m_pointer { 0 };
};
// It's valid to bitcast any LazyProperty to LazyCellProperty if you're just going to call get()
// or getConcurrently().
typedef LazyProperty<JSCell, JSCell> LazyCellProperty;
} // namespace JSC
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