ladybird/AK/Function.h

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/*
* Copyright (C) 2016 Apple Inc. All rights reserved.
* Copyright (c) 2021, Gunnar Beutner <gbeutner@serenityos.org>
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*
* 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 APPLE INC. AND ITS 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 APPLE INC. OR ITS 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/BitCast.h>
#include <AK/Noncopyable.h>
#include <AK/ScopeGuard.h>
#include <AK/StdLibExtras.h>
#include <AK/Types.h>
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namespace AK {
template<typename>
class Function;
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template<typename F>
inline constexpr bool IsFunctionPointer = (IsPointer<F> && IsFunction<RemovePointer<F>>);
// Not a function pointer, and not an lvalue reference.
template<typename F>
inline constexpr bool IsFunctionObject = (!IsFunctionPointer<F> && IsRvalueReference<F&&>);
template<typename Out, typename... In>
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class Function<Out(In...)> {
AK_MAKE_NONCOPYABLE(Function);
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public:
Function() = default;
Function(std::nullptr_t)
{
}
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~Function()
{
clear(false);
}
template<typename CallableType>
Function(CallableType&& callable) requires((IsFunctionObject<CallableType> && IsCallableWithArguments<CallableType, In...> && !IsSame<RemoveCVReference<CallableType>, Function>))
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{
init_with_callable(forward<CallableType>(callable));
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}
template<typename FunctionType>
Function(FunctionType f) requires((IsFunctionPointer<FunctionType> && IsCallableWithArguments<RemovePointer<FunctionType>, In...> && !IsSame<RemoveCVReference<FunctionType>, Function>))
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{
init_with_callable(move(f));
}
Function(Function&& other)
{
move_from(move(other));
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}
// Note: Despite this method being const, a mutable lambda _may_ modify its own captures.
Out operator()(In... in) const
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{
auto* wrapper = callable_wrapper();
VERIFY(wrapper);
++m_call_nesting_level;
ScopeGuard guard([this] {
if (--m_call_nesting_level == 0 && m_deferred_clear)
const_cast<Function*>(this)->clear(false);
});
return wrapper->call(forward<In>(in)...);
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}
explicit operator bool() const { return !!callable_wrapper(); }
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template<typename CallableType>
Function& operator=(CallableType&& callable) requires((IsFunctionObject<CallableType> && IsCallableWithArguments<CallableType, In...>))
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{
clear();
init_with_callable(forward<CallableType>(callable));
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return *this;
}
template<typename FunctionType>
Function& operator=(FunctionType f) requires((IsFunctionPointer<FunctionType> && IsCallableWithArguments<RemovePointer<FunctionType>, In...>))
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{
clear();
if (f)
init_with_callable(move(f));
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return *this;
}
Function& operator=(std::nullptr_t)
{
clear();
return *this;
}
Function& operator=(Function&& other)
{
if (this != &other) {
clear();
move_from(move(other));
}
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return *this;
}
private:
class CallableWrapperBase {
public:
virtual ~CallableWrapperBase() = default;
// Note: This is not const to allow storing mutable lambdas.
virtual Out call(In...) = 0;
virtual void destroy() = 0;
virtual void init_and_swap(u8*, size_t) = 0;
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};
template<typename CallableType>
class CallableWrapper final : public CallableWrapperBase {
AK_MAKE_NONMOVABLE(CallableWrapper);
AK_MAKE_NONCOPYABLE(CallableWrapper);
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public:
explicit CallableWrapper(CallableType&& callable)
: m_callable(move(callable))
{
}
Out call(In... in) final override
{
return m_callable(forward<In>(in)...);
}
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void destroy() final override
{
delete this;
}
// NOLINTNEXTLINE(readability-non-const-parameter) False positive; destination is used in a placement new expression
void init_and_swap(u8* destination, size_t size) final override
{
VERIFY(size >= sizeof(CallableWrapper));
new (destination) CallableWrapper { move(m_callable) };
}
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private:
CallableType m_callable;
};
enum class FunctionKind {
NullPointer,
Inline,
Outline,
};
CallableWrapperBase* callable_wrapper() const
{
switch (m_kind) {
case FunctionKind::NullPointer:
return nullptr;
case FunctionKind::Inline:
return bit_cast<CallableWrapperBase*>(&m_storage);
case FunctionKind::Outline:
return *bit_cast<CallableWrapperBase**>(&m_storage);
default:
VERIFY_NOT_REACHED();
}
}
void clear(bool may_defer = true)
{
bool called_from_inside_function = m_call_nesting_level > 0;
// NOTE: This VERIFY could fail because a Function is destroyed from within itself.
VERIFY(may_defer || !called_from_inside_function);
if (called_from_inside_function && may_defer) {
m_deferred_clear = true;
return;
}
m_deferred_clear = false;
auto* wrapper = callable_wrapper();
if (m_kind == FunctionKind::Inline) {
VERIFY(wrapper);
wrapper->~CallableWrapperBase();
} else if (m_kind == FunctionKind::Outline) {
VERIFY(wrapper);
wrapper->destroy();
}
m_kind = FunctionKind::NullPointer;
}
template<typename Callable>
void init_with_callable(Callable&& callable)
{
VERIFY(m_call_nesting_level == 0);
using WrapperType = CallableWrapper<Callable>;
if constexpr (sizeof(WrapperType) > inline_capacity) {
*bit_cast<CallableWrapperBase**>(&m_storage) = new WrapperType(forward<Callable>(callable));
m_kind = FunctionKind::Outline;
} else {
new (m_storage) WrapperType(forward<Callable>(callable));
m_kind = FunctionKind::Inline;
}
}
void move_from(Function&& other)
{
VERIFY(m_call_nesting_level == 0 && other.m_call_nesting_level == 0);
auto* other_wrapper = other.callable_wrapper();
switch (other.m_kind) {
case FunctionKind::NullPointer:
break;
case FunctionKind::Inline:
other_wrapper->init_and_swap(m_storage, inline_capacity);
m_kind = FunctionKind::Inline;
break;
case FunctionKind::Outline:
*bit_cast<CallableWrapperBase**>(&m_storage) = other_wrapper;
m_kind = FunctionKind::Outline;
break;
default:
VERIFY_NOT_REACHED();
}
other.m_kind = FunctionKind::NullPointer;
}
FunctionKind m_kind { FunctionKind::NullPointer };
bool m_deferred_clear { false };
mutable Atomic<u16> m_call_nesting_level { 0 };
// Empirically determined to fit most lambdas and functions.
static constexpr size_t inline_capacity = 4 * sizeof(void*);
alignas(max(alignof(CallableWrapperBase), alignof(CallableWrapperBase*))) u8 m_storage[inline_capacity];
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};
}
using AK::Function;