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https://github.com/SerenityOS/serenity
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a6a439243f
This step would ideally not have been necessary (increases amount of refactoring and templates necessary, which in turn increases build times), but it gives us a couple of nice properties: - SpinlockProtected inside Singleton (a very common combination) can now obtain any lock rank just via the template parameter. It was not previously possible to do this with SingletonInstanceCreator magic. - SpinlockProtected's lock rank is now mandatory; this is the majority of cases and allows us to see where we're still missing proper ranks. - The type already informs us what lock rank a lock has, which aids code readability and (possibly, if gdb cooperates) lock mismatch debugging. - The rank of a lock can no longer be dynamic, which is not something we wanted in the first place (or made use of). Locks randomly changing their rank sounds like a disaster waiting to happen. - In some places, we might be able to statically check that locks are taken in the right order (with the right lock rank checking implementation) as rank information is fully statically known. This refactoring even more exposes the fact that Mutex has no lock rank capabilites, which is not fixed here.
139 lines
3 KiB
C++
139 lines
3 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 KERNEL
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# include <Kernel/Arch/Processor.h>
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# include <Kernel/Locking/SpinlockProtected.h>
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# include <Kernel/ScopedCritical.h>
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#elif defined(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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#ifdef KERNEL
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template<typename T, Kernel::LockRank Rank>
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struct SingletonInstanceCreator<Kernel::SpinlockProtected<T, Rank>> {
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static Kernel::SpinlockProtected<T, Rank>* create()
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{
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return new Kernel::SpinlockProtected<T, Rank> {};
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}
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};
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#endif
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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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#ifdef KERNEL
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Kernel::ScopedCritical critical;
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#endif
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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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#ifdef KERNEL
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Kernel::Processor::wait_check();
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#else
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sched_yield();
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#endif
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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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