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117 lines
2.5 KiB
C++
117 lines
2.5 KiB
C++
/*
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* Copyright (c) 2020, the SerenityOS developers.
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*
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* SPDX-License-Identifier: BSD-2-Clause
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*/
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#pragma once
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#include <AK/Assertions.h>
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#include <AK/Atomic.h>
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#include <AK/Noncopyable.h>
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#ifdef AK_OS_WINDOWS
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// Forward declare to avoid pulling Windows.h into every file in existence.
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extern "C" __declspec(dllimport) void __stdcall Sleep(unsigned long);
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# ifndef sched_yield
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# define sched_yield() Sleep(0)
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# endif
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#else
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# include <sched.h>
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#endif
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#ifndef AK_OS_SERENITY
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# include <new>
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#endif
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namespace AK {
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template<typename T>
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struct SingletonInstanceCreator {
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static T* create()
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{
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return new T();
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}
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};
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template<typename T, T* (*InitFunction)() = SingletonInstanceCreator<T>::create>
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class Singleton {
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AK_MAKE_NONCOPYABLE(Singleton);
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AK_MAKE_NONMOVABLE(Singleton);
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public:
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Singleton() = default;
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template<bool allow_create = true>
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static T* get(Atomic<T*>& obj_var)
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{
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T* obj = obj_var.load(AK::memory_order_acquire);
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if (FlatPtr(obj) <= 0x1) {
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// If this is the first time, see if we get to initialize it
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if constexpr (allow_create) {
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if (obj == nullptr && obj_var.compare_exchange_strong(obj, (T*)0x1, AK::memory_order_acq_rel)) {
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// We're the first one
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obj = InitFunction();
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obj_var.store(obj, AK::memory_order_release);
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return obj;
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}
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}
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// Someone else was faster, wait until they're done
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while (obj == (T*)0x1) {
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sched_yield();
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obj = obj_var.load(AK::memory_order_acquire);
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}
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if constexpr (allow_create) {
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// We should always return an instance if we allow creating one
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VERIFY(obj != nullptr);
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}
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VERIFY(obj != (T*)0x1);
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}
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return obj;
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}
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T* ptr() const
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{
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return get(m_obj);
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}
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T* operator->() const
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{
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return ptr();
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}
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T& operator*() const
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{
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return *ptr();
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}
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operator T*() const
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{
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return ptr();
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}
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operator T&() const
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{
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return *ptr();
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}
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bool is_initialized() const
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{
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T* obj = m_obj.load(AK::MemoryOrder::memory_order_consume);
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return FlatPtr(obj) > 0x1;
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}
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void ensure_instance()
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{
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ptr();
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}
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private:
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mutable Atomic<T*> m_obj { nullptr };
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};
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}
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#if USING_AK_GLOBALLY
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using AK::Singleton;
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#endif
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