mirror of
https://github.com/SerenityOS/serenity
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1b2007cc7f
Instead of ballooning the size of the Function object, simply place the callable on the heap with a properly aligned address. This brings the alignment of Function down from ridiculous sizes like 64 bytes down to a manageable 8 bytes.
317 lines
10 KiB
C++
317 lines
10 KiB
C++
/*
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* Copyright (C) 2016 Apple Inc. All rights reserved.
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* Copyright (c) 2021, Gunnar Beutner <gbeutner@serenityos.org>
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* Copyright (c) 2018-2023, Andreas Kling <kling@serenityos.org>
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*
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* Redistribution and use in source and binary forms, with or without
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* modification, are permitted provided that the following conditions
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* are met:
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* 1. Redistributions of source code must retain the above copyright
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* notice, this list of conditions and the following disclaimer.
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* 2. Redistributions in binary form must reproduce the above copyright
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* notice, this list of conditions and the following disclaimer in the
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* documentation and/or other materials provided with the distribution.
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*
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* THIS SOFTWARE IS PROVIDED BY APPLE INC. AND ITS CONTRIBUTORS ``AS IS''
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* AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO,
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* THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
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* PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL APPLE INC. OR ITS CONTRIBUTORS
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* BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
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* CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
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* SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
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* INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
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* CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
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* ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF
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* THE POSSIBILITY OF SUCH DAMAGE.
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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/BitCast.h>
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#include <AK/Noncopyable.h>
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#include <AK/ScopeGuard.h>
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#include <AK/Span.h>
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#include <AK/StdLibExtras.h>
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#include <AK/Types.h>
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namespace AK {
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template<typename>
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class Function;
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template<typename F>
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inline constexpr bool IsFunctionPointer = (IsPointer<F> && IsFunction<RemovePointer<F>>);
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// Not a function pointer, and not an lvalue reference.
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template<typename F>
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inline constexpr bool IsFunctionObject = (!IsFunctionPointer<F> && IsRvalueReference<F&&>);
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template<typename Out, typename... In>
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class Function<Out(In...)> {
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AK_MAKE_NONCOPYABLE(Function);
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public:
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using FunctionType = Out(In...);
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using ReturnType = Out;
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#ifdef KERNEL
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constexpr static auto AccommodateExcessiveAlignmentRequirements = false;
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constexpr static size_t ExcessiveAlignmentThreshold = alignof(void*);
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#else
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constexpr static auto AccommodateExcessiveAlignmentRequirements = true;
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constexpr static size_t ExcessiveAlignmentThreshold = 16;
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#endif
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Function() = default;
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Function(nullptr_t)
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{
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}
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~Function()
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{
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clear(false);
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}
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[[nodiscard]] ReadonlyBytes raw_capture_range() const
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{
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if (!m_size)
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return {};
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if (auto* wrapper = callable_wrapper())
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return ReadonlyBytes { wrapper, m_size };
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return {};
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}
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template<typename CallableType>
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Function(CallableType&& callable)
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requires((IsFunctionObject<CallableType> && IsCallableWithArguments<CallableType, Out, In...> && !IsSame<RemoveCVReference<CallableType>, Function>))
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{
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init_with_callable(forward<CallableType>(callable), CallableKind::FunctionObject);
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}
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template<typename FunctionType>
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Function(FunctionType f)
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requires((IsFunctionPointer<FunctionType> && IsCallableWithArguments<RemovePointer<FunctionType>, Out, In...> && !IsSame<RemoveCVReference<FunctionType>, Function>))
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{
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init_with_callable(move(f), CallableKind::FunctionPointer);
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}
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Function(Function&& other)
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{
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move_from(move(other));
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}
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// Note: Despite this method being const, a mutable lambda _may_ modify its own captures.
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Out operator()(In... in) const
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{
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auto* wrapper = callable_wrapper();
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VERIFY(wrapper);
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++m_call_nesting_level;
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ScopeGuard guard([this] {
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if (--m_call_nesting_level == 0 && m_deferred_clear)
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const_cast<Function*>(this)->clear(false);
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});
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return wrapper->call(forward<In>(in)...);
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}
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explicit operator bool() const { return !!callable_wrapper(); }
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template<typename CallableType>
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Function& operator=(CallableType&& callable)
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requires((IsFunctionObject<CallableType> && IsCallableWithArguments<CallableType, Out, In...>))
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{
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clear();
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init_with_callable(forward<CallableType>(callable), CallableKind::FunctionObject);
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return *this;
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}
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template<typename FunctionType>
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Function& operator=(FunctionType f)
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requires((IsFunctionPointer<FunctionType> && IsCallableWithArguments<RemovePointer<FunctionType>, Out, In...>))
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{
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clear();
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if (f)
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init_with_callable(move(f), CallableKind::FunctionPointer);
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return *this;
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}
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Function& operator=(nullptr_t)
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{
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clear();
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return *this;
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}
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Function& operator=(Function&& other)
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{
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if (this != &other) {
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clear();
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move_from(move(other));
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}
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return *this;
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}
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private:
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enum class CallableKind {
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FunctionPointer,
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FunctionObject,
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};
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class CallableWrapperBase {
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public:
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virtual ~CallableWrapperBase() = default;
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// Note: This is not const to allow storing mutable lambdas.
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virtual Out call(In...) = 0;
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virtual void destroy() = 0;
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virtual void init_and_swap(u8*, size_t) = 0;
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};
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template<typename CallableType>
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class CallableWrapper final : public CallableWrapperBase {
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AK_MAKE_NONMOVABLE(CallableWrapper);
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AK_MAKE_NONCOPYABLE(CallableWrapper);
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public:
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explicit CallableWrapper(CallableType&& callable)
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: m_callable(move(callable))
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{
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}
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Out call(In... in) final override
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{
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return m_callable(forward<In>(in)...);
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}
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void destroy() final override
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{
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delete this;
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}
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// NOLINTNEXTLINE(readability-non-const-parameter) False positive; destination is used in a placement new expression
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void init_and_swap(u8* destination, size_t size) final override
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{
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VERIFY(size >= sizeof(CallableWrapper));
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new (destination) CallableWrapper { move(m_callable) };
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}
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private:
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CallableType m_callable;
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};
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enum class FunctionKind {
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NullPointer,
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Inline,
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Outline,
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};
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CallableWrapperBase* callable_wrapper() const
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{
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switch (m_kind) {
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case FunctionKind::NullPointer:
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return nullptr;
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case FunctionKind::Inline:
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return bit_cast<CallableWrapperBase*>(&m_storage);
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case FunctionKind::Outline:
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return *bit_cast<CallableWrapperBase**>(&m_storage);
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default:
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VERIFY_NOT_REACHED();
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}
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}
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void clear(bool may_defer = true)
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{
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bool called_from_inside_function = m_call_nesting_level > 0;
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// NOTE: This VERIFY could fail because a Function is destroyed from within itself.
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VERIFY(may_defer || !called_from_inside_function);
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if (called_from_inside_function && may_defer) {
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m_deferred_clear = true;
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return;
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}
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m_deferred_clear = false;
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auto* wrapper = callable_wrapper();
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if (m_kind == FunctionKind::Inline) {
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VERIFY(wrapper);
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wrapper->~CallableWrapperBase();
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} else if (m_kind == FunctionKind::Outline) {
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VERIFY(wrapper);
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wrapper->destroy();
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}
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m_kind = FunctionKind::NullPointer;
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}
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template<typename Callable>
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void init_with_callable(Callable&& callable, CallableKind callable_kind)
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{
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if constexpr (alignof(Callable) > ExcessiveAlignmentThreshold && !AccommodateExcessiveAlignmentRequirements) {
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static_assert(
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alignof(Callable) <= ExcessiveAlignmentThreshold,
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"This callable object has a very large alignment requirement, "
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"check your capture list if it is a lambda expression, "
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"and make sure your callable object is not excessively aligned.");
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}
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VERIFY(m_call_nesting_level == 0);
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using WrapperType = CallableWrapper<Callable>;
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#ifndef KERNEL
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if constexpr (alignof(Callable) > inline_alignment || sizeof(WrapperType) > inline_capacity) {
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*bit_cast<CallableWrapperBase**>(&m_storage) = new WrapperType(forward<Callable>(callable));
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m_kind = FunctionKind::Outline;
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} else {
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#endif
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static_assert(sizeof(WrapperType) <= inline_capacity);
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new (m_storage) WrapperType(forward<Callable>(callable));
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m_kind = FunctionKind::Inline;
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#ifndef KERNEL
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}
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#endif
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if (callable_kind == CallableKind::FunctionObject)
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m_size = sizeof(WrapperType);
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else
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m_size = 0;
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}
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void move_from(Function&& other)
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{
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VERIFY(m_call_nesting_level == 0 && other.m_call_nesting_level == 0);
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auto* other_wrapper = other.callable_wrapper();
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m_size = other.m_size;
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switch (other.m_kind) {
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case FunctionKind::NullPointer:
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break;
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case FunctionKind::Inline:
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other_wrapper->init_and_swap(m_storage, inline_capacity);
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m_kind = FunctionKind::Inline;
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break;
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case FunctionKind::Outline:
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*bit_cast<CallableWrapperBase**>(&m_storage) = other_wrapper;
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m_kind = FunctionKind::Outline;
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break;
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default:
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VERIFY_NOT_REACHED();
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}
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other.m_kind = FunctionKind::NullPointer;
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}
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size_t m_size { 0 };
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FunctionKind m_kind { FunctionKind::NullPointer };
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bool m_deferred_clear { false };
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mutable Atomic<u16> m_call_nesting_level { 0 };
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static constexpr size_t inline_alignment = max(alignof(CallableWrapperBase), alignof(CallableWrapperBase*));
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#ifndef KERNEL
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// Empirically determined to fit most lambdas and functions.
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static constexpr size_t inline_capacity = 4 * sizeof(void*);
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#else
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// FIXME: Try to decrease this.
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static constexpr size_t inline_capacity = 6 * sizeof(void*);
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#endif
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alignas(inline_alignment) u8 m_storage[inline_capacity];
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};
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}
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#if USING_AK_GLOBALLY
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using AK::Function;
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using AK::IsCallableWithArguments;
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#endif
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