ladybird/AK/Function.h
Ali Mohammad Pur f96a3c002a Everywhere: Stop shoving things into ::std and mentioning them as such
Note that this still keeps the old behaviour of putting things in std by
default on serenity so the tools can be happy, but if USING_AK_GLOBALLY
is unset, AK behaves like a good citizen and doesn't try to put things
in the ::std namespace.

std::nothrow_t and its friends get to stay because I'm being told that
compilers assume things about them and I can't yeet them into a
different namespace...for now.
2022-12-14 11:44:32 +01:00

275 lines
8.5 KiB
C++

/*
* Copyright (C) 2016 Apple Inc. All rights reserved.
* Copyright (c) 2021, Gunnar Beutner <gbeutner@serenityos.org>
*
* 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>
namespace AK {
template<typename>
class Function;
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>
class Function<Out(In...)> {
AK_MAKE_NONCOPYABLE(Function);
public:
using ReturnType = Out;
Function() = default;
Function(nullptr_t)
{
}
~Function()
{
clear(false);
}
template<typename CallableType>
Function(CallableType&& callable)
requires((IsFunctionObject<CallableType> && IsCallableWithArguments<CallableType, In...> && !IsSame<RemoveCVReference<CallableType>, Function>))
{
init_with_callable(forward<CallableType>(callable));
}
template<typename FunctionType>
Function(FunctionType f)
requires((IsFunctionPointer<FunctionType> && IsCallableWithArguments<RemovePointer<FunctionType>, In...> && !IsSame<RemoveCVReference<FunctionType>, Function>))
{
init_with_callable(move(f));
}
Function(Function&& other)
{
move_from(move(other));
}
// Note: Despite this method being const, a mutable lambda _may_ modify its own captures.
Out operator()(In... in) const
{
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)...);
}
explicit operator bool() const { return !!callable_wrapper(); }
template<typename CallableType>
Function& operator=(CallableType&& callable)
requires((IsFunctionObject<CallableType> && IsCallableWithArguments<CallableType, In...>))
{
clear();
init_with_callable(forward<CallableType>(callable));
return *this;
}
template<typename FunctionType>
Function& operator=(FunctionType f)
requires((IsFunctionPointer<FunctionType> && IsCallableWithArguments<RemovePointer<FunctionType>, In...>))
{
clear();
if (f)
init_with_callable(move(f));
return *this;
}
Function& operator=(nullptr_t)
{
clear();
return *this;
}
Function& operator=(Function&& other)
{
if (this != &other) {
clear();
move_from(move(other));
}
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;
};
template<typename CallableType>
class CallableWrapper final : public CallableWrapperBase {
AK_MAKE_NONMOVABLE(CallableWrapper);
AK_MAKE_NONCOPYABLE(CallableWrapper);
public:
explicit CallableWrapper(CallableType&& callable)
: m_callable(move(callable))
{
}
Out call(In... in) final override
{
return m_callable(forward<In>(in)...);
}
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) };
}
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>;
#ifndef KERNEL
if constexpr (sizeof(WrapperType) > inline_capacity) {
*bit_cast<CallableWrapperBase**>(&m_storage) = new WrapperType(forward<Callable>(callable));
m_kind = FunctionKind::Outline;
} else {
#endif
static_assert(sizeof(WrapperType) <= inline_capacity);
new (m_storage) WrapperType(forward<Callable>(callable));
m_kind = FunctionKind::Inline;
#ifndef KERNEL
}
#endif
}
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 };
#ifndef KERNEL
// Empirically determined to fit most lambdas and functions.
static constexpr size_t inline_capacity = 4 * sizeof(void*);
#else
// FIXME: Try to decrease this.
static constexpr size_t inline_capacity = 6 * sizeof(void*);
#endif
alignas(max(alignof(CallableWrapperBase), alignof(CallableWrapperBase*))) u8 m_storage[inline_capacity];
};
}
#if USING_AK_GLOBALLY
using AK::Function;
#endif