bound_method.h

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/* SPDX-License-Identifier: LGPL-2.1-or-later */
/*
 * Copyright (C) 2019, Google Inc.
 *
 * Method bind and invocation
 */

#pragma once

#include <memory>
#include <tuple>
#include <type_traits>
#include <utility>

namespace libcamera {

class Object;

enum ConnectionType {
    ConnectionTypeAuto,
    ConnectionTypeDirect,
    ConnectionTypeQueued,
    ConnectionTypeBlocking,
};

class BoundMethodPackBase
{
public:
    virtual ~BoundMethodPackBase() = default;
};

template<typename R, typename... Args>
class BoundMethodPack : public BoundMethodPackBase
{
public:
    BoundMethodPack(const Args &... args)
        : args_(args...)
    {
    }

    R returnValue()
    {
        return ret_;
    }

    std::tuple<typename std::remove_reference_t<Args>...> args_;
    R ret_;
};

template<typename... Args>
class BoundMethodPack<void, Args...> : public BoundMethodPackBase
{
public:
    BoundMethodPack(const Args &... args)
        : args_(args...)
    {
    }

    void returnValue()
    {
    }

    std::tuple<typename std::remove_reference_t<Args>...> args_;
};

class BoundMethodBase
{
public:
    BoundMethodBase(void *obj, Object *object, ConnectionType type)
        : obj_(obj), object_(object), connectionType_(type)
    {
    }
    virtual ~BoundMethodBase() = default;

    template<typename T, std::enable_if_t<!std::is_same<Object, T>::value> * = nullptr>
    bool match(T *obj) { return obj == obj_; }
    bool match(Object *object) { return object == object_; }

    Object *object() const { return object_; }

    virtual void invokePack(BoundMethodPackBase *pack) = 0;

protected:
    bool activatePack(std::shared_ptr<BoundMethodPackBase> pack,
              bool deleteMethod);

    void *obj_;
    Object *object_;

private:
    ConnectionType connectionType_;
};

template<typename R, typename... Args>
class BoundMethodArgs : public BoundMethodBase
{
public:
    using PackType = BoundMethodPack<R, Args...>;

private:
    template<std::size_t... I, typename T = R>
    std::enable_if_t<!std::is_void<T>::value, void>
    invokePack(BoundMethodPackBase *pack, std::index_sequence<I...>)
    {
        PackType *args = static_cast<PackType *>(pack);
        args->ret_ = invoke(std::get<I>(args->args_)...);
    }

    template<std::size_t... I, typename T = R>
    std::enable_if_t<std::is_void<T>::value, void>
    invokePack(BoundMethodPackBase *pack, std::index_sequence<I...>)
    {
        /* args is effectively unused when the sequence I is empty. */
        PackType *args [[gnu::unused]] = static_cast<PackType *>(pack);
        invoke(std::get<I>(args->args_)...);
    }

public:
    BoundMethodArgs(void *obj, Object *object, ConnectionType type)
        : BoundMethodBase(obj, object, type) {}

    void invokePack(BoundMethodPackBase *pack) override
    {
        invokePack(pack, std::make_index_sequence<sizeof...(Args)>{});
    }

    virtual R activate(Args... args, bool deleteMethod = false) = 0;
    virtual R invoke(Args... args) = 0;
};

template<typename T, typename R, typename Func, typename... Args>
class BoundMethodFunctor : public BoundMethodArgs<R, Args...>
{
public:
    using PackType = typename BoundMethodArgs<R, Args...>::PackType;

    BoundMethodFunctor(T *obj, Object *object, Func func,
               ConnectionType type = ConnectionTypeAuto)
        : BoundMethodArgs<R, Args...>(obj, object, type), func_(func)
    {
    }

    R activate(Args... args, bool deleteMethod = false) override
    {
        if (!this->object_)
            return func_(args...);

        auto pack = std::make_shared<PackType>(args...);
        bool sync = BoundMethodBase::activatePack(pack, deleteMethod);
        return sync ? pack->returnValue() : R();
    }

    R invoke(Args... args) override
    {
        return func_(args...);
    }

private:
    Func func_;
};

template<typename T, typename R, typename... Args>
class BoundMethodMember : public BoundMethodArgs<R, Args...>
{
public:
    using PackType = typename BoundMethodArgs<R, Args...>::PackType;

    BoundMethodMember(T *obj, Object *object, R (T::*func)(Args...),
              ConnectionType type = ConnectionTypeAuto)
        : BoundMethodArgs<R, Args...>(obj, object, type), func_(func)
    {
    }

    bool match(R (T::*func)(Args...)) const { return func == func_; }

    R activate(Args... args, bool deleteMethod = false) override
    {
        if (!this->object_) {
            T *obj = static_cast<T *>(this->obj_);
            return (obj->*func_)(args...);
        }

        auto pack = std::make_shared<PackType>(args...);
        bool sync = BoundMethodBase::activatePack(pack, deleteMethod);
        return sync ? pack->returnValue() : R();
    }

    R invoke(Args... args) override
    {
        T *obj = static_cast<T *>(this->obj_);
        return (obj->*func_)(args...);
    }

private:
    R (T::*func_)(Args...);
};

template<typename R, typename... Args>
class BoundMethodStatic : public BoundMethodArgs<R, Args...>
{
public:
    BoundMethodStatic(R (*func)(Args...))
        : BoundMethodArgs<R, Args...>(nullptr, nullptr, ConnectionTypeAuto),
          func_(func)
    {
    }

    bool match(R (*func)(Args...)) const { return func == func_; }

    R activate(Args... args, [[maybe_unused]] bool deleteMethod = false) override
    {
        return (*func_)(args...);
    }

    R invoke(Args...) override
    {
        return R();
    }

private:
    R (*func_)(Args...);
};

} /* namespace libcamera */