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/*
* Copyright (c) 2020, the SerenityOS developers.
* 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 THE COPYRIGHT HOLDERS AND 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 THE COPYRIGHT HOLDER OR 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 <AK/Assertions.h>
#include <AK/Atomic.h>
#include <AK/Noncopyable.h>
#ifdef KERNEL
# include <Kernel/Arch/x86/CPU.h>
#endif
#ifndef __serenity__
# include <new>
#endif
namespace AK {
template<typename T>
struct SingletonInstanceCreator {
static T* create()
{
return new T();
}
};
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(T*& obj_var)
{
T* obj = AK::atomic_load(&obj_var, 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 && AK::atomic_compare_exchange_strong(&obj_var, obj, (T*)0x1, AK::memory_order_acq_rel)) {
// We're the first one
obj = InitFunction();
AK::atomic_store(&obj_var, 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
// TODO: yield
#endif
obj = AK::atomic_load(&obj_var, 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 = AK::atomic_load(&m_obj, AK::memory_order_consume);
return FlatPtr(obj) > 0x1;
}
void ensure_instance()
{
ptr();
}
private:
mutable T* m_obj { nullptr }; // atomic
};
}
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