#pragma once
#include <type_traits>
#include <utility>
#include <wtf/ForbidHeapAllocation.h>
#include <wtf/MainThread.h>
#include <wtf/RefCounted.h>
namespace WTF {
struct AnyThreadsAccessTraits {
static void assertAccess()
{
}
};
struct MainThreadAccessTraits {
static void assertAccess()
{
ASSERT(isMainThread());
}
};
template<typename T, typename AccessTraits> class NeverDestroyed {
WTF_MAKE_NONCOPYABLE(NeverDestroyed);
WTF_FORBID_HEAP_ALLOCATION;
public:
template<typename... Args> NeverDestroyed(Args&&... args)
{
AccessTraits::assertAccess();
MaybeRelax<T>(new (storagePointer()) T(std::forward<Args>(args)...));
}
NeverDestroyed(NeverDestroyed&& other)
{
AccessTraits::assertAccess();
MaybeRelax<T>(new (storagePointer()) T(WTFMove(*other.storagePointer())));
}
operator T&() { return *storagePointer(); }
T& get() { return *storagePointer(); }
T* operator->() { return storagePointer(); }
operator const T&() const { return *storagePointer(); }
const T& get() const { return *storagePointer(); }
const T* operator->() const { return storagePointer(); }
private:
using PointerType = typename std::remove_const<T>::type*;
PointerType storagePointer() const
{
AccessTraits::assertAccess();
return const_cast<PointerType>(reinterpret_cast<const T*>(&m_storage));
}
template<typename PtrType, bool ShouldRelax = std::is_base_of<RefCountedBase, PtrType>::value> struct MaybeRelax {
explicit MaybeRelax(PtrType*) { }
};
template<typename PtrType> struct MaybeRelax<PtrType, true> {
explicit MaybeRelax(PtrType* ptr) { ptr->relaxAdoptionRequirement(); }
};
typename std::aligned_storage<sizeof(T), std::alignment_of<T>::value>::type m_storage;
};
template<typename T, typename AccessTraits = AnyThreadsAccessTraits> NeverDestroyed<T, AccessTraits> makeNeverDestroyed(T&&);
template<typename T, typename AccessTraits> class LazyNeverDestroyed {
WTF_MAKE_NONCOPYABLE(LazyNeverDestroyed);
WTF_FORBID_HEAP_ALLOCATION;
public:
LazyNeverDestroyed() = default;
template<typename... Args>
void construct(Args&&... args)
{
AccessTraits::assertAccess();
constructWithoutAccessCheck(std::forward<Args>(args)...);
}
template<typename... Args>
void constructWithoutAccessCheck(Args&&... args)
{
ASSERT(!m_isConstructed);
#if ASSERT_ENABLED
m_isConstructed = true;
#endif
MaybeRelax<T>(new (storagePointerWithoutAccessCheck()) T(std::forward<Args>(args)...));
}
operator T&() { return *storagePointer(); }
T& get() { return *storagePointer(); }
T* operator->() { return storagePointer(); }
operator const T&() const { return *storagePointer(); }
const T& get() const { return *storagePointer(); }
const T* operator->() const { return storagePointer(); }
#if ASSERT_ENABLED
bool isConstructed() const { return m_isConstructed; }
#endif
private:
using PointerType = typename std::remove_const<T>::type*;
PointerType storagePointerWithoutAccessCheck() const
{
ASSERT(m_isConstructed);
return const_cast<PointerType>(reinterpret_cast<const T*>(&m_storage));
}
PointerType storagePointer() const
{
AccessTraits::assertAccess();
return storagePointerWithoutAccessCheck();
}
template<typename PtrType, bool ShouldRelax = std::is_base_of<RefCountedBase, PtrType>::value> struct MaybeRelax {
explicit MaybeRelax(PtrType*) { }
};
template<typename PtrType> struct MaybeRelax<PtrType, true> {
explicit MaybeRelax(PtrType* ptr) { ptr->relaxAdoptionRequirement(); }
};
#if ASSERT_ENABLED
bool m_isConstructed;
#endif
typename std::aligned_storage<sizeof(T), std::alignment_of<T>::value>::type m_storage;
};
template<typename T, typename AccessTraits> inline NeverDestroyed<T, AccessTraits> makeNeverDestroyed(T&& argument)
{
return WTFMove(argument);
}
template<typename T>
using MainThreadNeverDestroyed = NeverDestroyed<T, MainThreadAccessTraits>;
template<typename T>
using MainThreadLazyNeverDestroyed = LazyNeverDestroyed<T, MainThreadAccessTraits>;
}
using WTF::LazyNeverDestroyed;
using WTF::NeverDestroyed;
using WTF::makeNeverDestroyed;
using WTF::MainThreadNeverDestroyed;
using WTF::MainThreadLazyNeverDestroyed;
using WTF::AnyThreadsAccessTraits;
using WTF::MainThreadAccessTraits;