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/*
* Copyright (c) 2020, the SerenityOS developers.
*
* SPDX-License-Identifier: BSD-2-Clause
*/
#pragma once
#include <AK/Assertions.h>
#include <AK/Atomic.h>
#include <AK/Noncopyable.h>
#ifdef KERNEL
# include <Kernel/Arch/Processor.h>
# include <Kernel/Arch/ScopedCritical.h>
# include <Kernel/Locking/SpinlockProtected.h>
#elif defined(AK_OS_WINDOWS)
// Forward declare to avoid pulling Windows.h into every file in existence.
extern "C" __declspec(dllimport) void __stdcall Sleep(unsigned long);
# ifndef sched_yield
# define sched_yield() Sleep(0)
# endif
#else
# include <sched.h>
#endif
#ifndef __serenity__
# include <new>
#endif
namespace AK {
template<typename T>
struct SingletonInstanceCreator {
static T* create()
{
return new T();
}
};
#ifdef KERNEL
// FIXME: Find a nice way of injecting the lock rank into the singleton.
template<typename T>
struct SingletonInstanceCreator<Kernel::SpinlockProtected<T>> {
static Kernel::SpinlockProtected<T>* create()
{
return new Kernel::SpinlockProtected<T> { Kernel::LockRank::None };
}
};
#endif
template<typename T, T* (*InitFunction)() = SingletonInstanceCreator<T>::create>
class Singleton {
AK_MAKE_NONCOPYABLE(Singleton);
AK_MAKE_NONMOVABLE(Singleton);
public:
Singleton() = default;
template<bool allow_create = true>
static T* get(Atomic<T*>& obj_var)
{
T* obj = obj_var.load(AK::memory_order_acquire);
if (FlatPtr(obj) <= 0x1) {
// If this is the first time, see if we get to initialize it
#ifdef KERNEL
Kernel::ScopedCritical critical;
#endif
if constexpr (allow_create) {
if (obj == nullptr && obj_var.compare_exchange_strong(obj, (T*)0x1, AK::memory_order_acq_rel)) {
// We're the first one
obj = InitFunction();
obj_var.store(obj, AK::memory_order_release);
return obj;
}
}
// Someone else was faster, wait until they're done
while (obj == (T*)0x1) {
#ifdef KERNEL
Kernel::Processor::wait_check();
#else
sched_yield();
#endif
obj = obj_var.load(AK::memory_order_acquire);
}
if constexpr (allow_create) {
// We should always return an instance if we allow creating one
VERIFY(obj != nullptr);
}
VERIFY(obj != (T*)0x1);
}
return obj;
}
T* ptr() const
{
return get(m_obj);
}
T* operator->() const
{
return ptr();
}
T& operator*() const
{
return *ptr();
}
operator T*() const
{
return ptr();
}
operator T&() const
{
return *ptr();
}
bool is_initialized() const
{
T* obj = m_obj.load(AK::MemoryOrder::memory_order_consume);
return FlatPtr(obj) > 0x1;
}
void ensure_instance()
{
ptr();
}
private:
mutable Atomic<T*> m_obj { nullptr };
};
}
using AK::Singleton;
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