callback.h

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/*
 * Copyright (c) 2005,2006 INRIA
 *
 * SPDX-License-Identifier: GPL-2.0-only
 *
 * Authors: Mathieu Lacage <mathieu.lacage@sophia.inria.fr>
 *          Stefano Avallone <stavallo@unina.it>
 */
 
#ifndef CALLBACK_H
#define CALLBACK_H
 
#include "attribute-helper.h"
#include "attribute.h"
#include "demangle.h"
#include "fatal-error.h"
#include "ptr.h"
#include "simple-ref-count.h"
 
#include <functional>
#include <memory>
#include <typeinfo>
#include <utility>
#include <vector>
 
/**
 * @file
 * @ingroup callback
 * Declaration of the various callback functions.
 */
 
namespace ns3
{
 
// Define the doxygen subgroups all at once,
// since the implementations are interleaved.
 
/**
 * @ingroup core
 * @defgroup callback Callbacks
 * @brief Wrap functions, objects, and arguments into self contained callbacks.
 *
 * Wrapped callbacks are at the heart of scheduling events in the
 * simulator.
 */
/**
 * @ingroup callback
 * @defgroup callbackimpl Callback Implementation
 * Callback implementation classes
 */
/**
 * @ingroup callbackimpl
 * @defgroup makeboundcallback MakeBoundCallback from functions bound with up to three arguments.
 *
 * Build bound Callbacks which take varying numbers of arguments,
 * and potentially returning a value.
 *
 * @internal
 *
 * The following is experimental code. It works but we have
 * not yet determined whether or not it is really useful and whether
 * or not we really want to use it.
 */
 
/**
 * @ingroup callbackimpl
 * Abstract base class for CallbackImpl
 * Provides reference counting and equality test.
 */
class CallbackImplBase : public SimpleRefCount<CallbackImplBase>
{
  public:
    /** Virtual destructor */
    virtual ~CallbackImplBase()
    {
    }
 
    /**
     * Equality test
     *
     * @param [in] other Callback Ptr
     * @return \c true if we are equal
     */
    virtual bool IsEqual(Ptr<const CallbackImplBase> other) const = 0;
    /**
     * Get the name of this object type.
     * @return The object type as a string.
     */
    virtual std::string GetTypeid() const = 0;
 
  protected:
    /**
     * Helper to get the C++ typeid as a string.
     *
     * @tparam T \explicit The type of the argument.
     * @returns The result of applying typeid to the template type \pname{T}.
     */
    template <typename T>
    static std::string GetCppTypeid()
    {
        std::string typeName;
        try
        {
            typeName = typeid(T).name();
            typeName = Demangle(typeName);
        }
        catch (const std::bad_typeid& e)
        {
            typeName = e.what();
        }
        return typeName;
    }
};
 
/**
 * @ingroup callbackimpl
 * Abstract base class for CallbackComponent.
 * Provides equality test.
 */
class CallbackComponentBase
{
  public:
    /** Virtual destructor */
    virtual ~CallbackComponentBase()
    {
    }
 
    /**
     * Equality test
     *
     * @param [in] other CallbackComponent Ptr
     * @return \c true if we are equal
     */
    virtual bool IsEqual(std::shared_ptr<const CallbackComponentBase> other) const = 0;
};
 
/**
 * @ingroup callbackimpl
 * Stores a component of a callback, i.e., the callable object
 * or a bound argument. The purpose of this class is to test
 * the equality of the components of two callbacks.
 *
 * @tparam T The type of the callback component.
 * @tparam isComparable whether this callback component can be compared to others of the same type
 */
template <typename T, bool isComparable = true>
class CallbackComponent : public CallbackComponentBase
{
  public:
    /**
     * Constructor
     *
     * @param [in] t The value of the callback component
     */
    CallbackComponent(const T& t)
        : m_comp(t)
    {
    }
 
    /**
     * Equality test between the values of two components
     *
     * @param [in] other CallbackComponentBase Ptr
     * @return \c true if we are equal
     */
    bool IsEqual(std::shared_ptr<const CallbackComponentBase> other) const override
    {
        auto p = std::dynamic_pointer_cast<const CallbackComponent<T>>(other);
 
        // other must have the same type and value as ours
        return !(p == nullptr || p->m_comp != m_comp);
    }
 
  private:
    T m_comp; //!< the value of the callback component
};
 
/**
 * @ingroup callbackimpl
 * Partial specialization of class CallbackComponent with isComparable equal
 * to false. This is required to handle callable objects (such as lambdas and
 * objects returned by std::function and std::bind) that do not provide the
 * equality operator. Given that these objects cannot be compared and the only
 * purpose of the class CallbackComponent is to compare values, no object is
 * stored in this specialized class.
 *
 * @tparam T The type of the callback component.
 */
template <typename T>
class CallbackComponent<T, false> : public CallbackComponentBase
{
  public:
    /**
     * Constructor
     *
     * @param [in] t The value of the callback component
     */
    CallbackComponent(const T& t)
    {
    }
 
    /**
     * Equality test between functions
     *
     * @param [in] other CallbackParam Ptr
     * @return \c true if we are equal
     */
    bool IsEqual(std::shared_ptr<const CallbackComponentBase> other) const override
    {
        return false;
    }
};
 
/// Vector of callback components
typedef std::vector<std::shared_ptr<CallbackComponentBase>> CallbackComponentVector;
 
/**
 * @ingroup callbackimpl
 * CallbackImpl class with varying numbers of argument types
 *
 * @tparam R \explicit The return type of the Callback.
 * @tparam UArgs \explicit The types of any arguments to the Callback.
 */
template <typename R, typename... UArgs>
class CallbackImpl : public CallbackImplBase
{
  public:
    /**
     * Constructor.
     *
     * @param func the callable object
     * @param components the callback components (callable object and bound arguments)
     */
    CallbackImpl(std::function<R(UArgs...)> func, const CallbackComponentVector& components)
        : m_func(func),
          m_components(components)
    {
    }
 
    /**
     * Get the stored function.
     * @return A const reference to the stored function.
     */
    const std::function<R(UArgs...)>& GetFunction() const
    {
        return m_func;
    }
 
    /**
     * Get the vector of callback components.
     * @return A const reference to the vector of callback components.
     */
    const CallbackComponentVector& GetComponents() const
    {
        return m_components;
    }
 
    /**
     * Function call operator.
     *
     * @param uargs The arguments to the Callback.
     * @return Callback value
     */
    R operator()(UArgs... uargs) const
    {
        return m_func(uargs...);
    }
 
    bool IsEqual(Ptr<const CallbackImplBase> other) const override
    {
        const auto otherDerived =
            dynamic_cast<const CallbackImpl<R, UArgs...>*>(PeekPointer(other));
 
        if (otherDerived == nullptr)
        {
            return false;
        }
 
        // if the two callback implementations are made of a distinct number of
        // components, they are different
        if (m_components.size() != otherDerived->GetComponents().size())
        {
            return false;
        }
 
        // the two functions are equal if they compare equal or the shared pointers
        // point to the same locations
        if (!m_components.at(0)->IsEqual(otherDerived->GetComponents().at(0)) &&
            m_components.at(0) != otherDerived->GetComponents().at(0))
        {
            return false;
        }
 
        // check if the remaining components are equal one by one
        for (std::size_t i = 1; i < m_components.size(); i++)
        {
            if (!m_components.at(i)->IsEqual(otherDerived->GetComponents().at(i)))
            {
                return false;
            }
        }
 
        return true;
    }
 
    std::string GetTypeid() const override
    {
        return DoGetTypeid();
    }
 
    /** @copydoc GetTypeid() */
    static std::string DoGetTypeid()
    {
        static std::vector<std::string> vec = {GetCppTypeid<R>(), GetCppTypeid<UArgs>()...};
 
        static std::string id("CallbackImpl<");
        for (auto& s : vec)
        {
            id.append(s + ",");
        }
        if (id.back() == ',')
        {
            id.pop_back();
        }
        id.push_back('>');
 
        return id;
    }
 
  private:
    /// Stores the callable object associated with this callback (as a lambda)
    std::function<R(UArgs...)> m_func;
 
    /// Stores the original callable object and the bound arguments, if any
    std::vector<std::shared_ptr<CallbackComponentBase>> m_components;
};
 
/**
 * @ingroup callbackimpl
 * Base class for Callback class.
 * Provides pimpl abstraction.
 */
class CallbackBase
{
  public:
    CallbackBase()
        : m_impl()
    {
    }
 
    /** @return The impl pointer */
    Ptr<CallbackImplBase> GetImpl() const
    {
        return m_impl;
    }
 
  protected:
    /**
     * Construct from a pimpl
     * @param [in] impl The CallbackImplBase Ptr
     */
    CallbackBase(Ptr<CallbackImplBase> impl)
        : m_impl(impl)
    {
    }
 
    Ptr<CallbackImplBase> m_impl; //!< the pimpl
};
 
/**
 * @ingroup callback
 * @brief Callback template class
 *
 * This class template implements the Functor Design Pattern.
 * It is used to declare the type of a Callback:
 *  - the first non-optional template argument represents
 *    the return type of the callback.
 *  - the remaining (optional) template arguments represent
 *    the type of the subsequent arguments to the callback.
 *
 * Callback instances are built with the \ref MakeCallback
 * template functions. Callback instances have POD semantics:
 * the memory they allocate is managed automatically, without
 * user intervention which allows you to pass around Callback
 * instances by value.
 *
 * Sample code which shows how to use this class template
 * as well as the function templates \ref MakeCallback :
 * @include src/core/examples/main-callback.cc
 *
 * @internal
 * This code was originally written based on the techniques
 * described in http://www.codeproject.com/cpp/TTLFunction.asp
 * It was subsequently rewritten to follow the architecture
 * outlined in "Modern C++ Design" by Andrei Alexandrescu in
 * chapter 5, "Generalized Functors".
 *
 * This code uses:
 *   - default template parameters to saves users from having to
 *     specify empty parameters when the number of parameters
 *     is smaller than the maximum supported number
 *   - the pimpl idiom: the Callback class is passed around by
 *     value and delegates the crux of the work to its pimpl
 *     pointer.
 *   - a reference list implementation to implement the Callback's
 *     value semantics.
 *
 * This code most notably departs from the alexandrescu
 * implementation in that it does not use type lists to specify
 * and pass around the types of the callback arguments.
 * Of course, it also does not use copy-destruction semantics
 * and relies on a reference list rather than autoPtr to hold
 * the pointer.
 *
 * @see attribute_Callback
 *
 * @tparam R \explicit The return type of the Callback.
 * @tparam UArgs \explicit The types of any arguments to the Callback.
 */
template <typename R, typename... UArgs>
class Callback : public CallbackBase
{
    template <typename ROther, typename... UArgsOther>
    friend class Callback;
 
  public:
    Callback()
    {
    }
 
    /**
     * Construct from a CallbackImpl pointer
     *
     * @param [in] impl The CallbackImpl Ptr
     */
    Callback(const Ptr<CallbackImpl<R, UArgs...>>& impl)
        : CallbackBase(impl)
    {
    }
 
    /**
     * Construct from another callback and bind some arguments (if any)
     *
     * @tparam BArgs \deduced The types of the bound arguments
     * @param [in] cb The existing callback
     * @param [in] bargs The values of the bound arguments
     */
    template <typename... BArgs>
    Callback(const Callback<R, BArgs..., UArgs...>& cb, BArgs... bargs)
    {
        auto f = cb.DoPeekImpl()->GetFunction();
 
        CallbackComponentVector components(cb.DoPeekImpl()->GetComponents());
        components.insert(components.end(),
                          {std::make_shared<CallbackComponent<std::decay_t<BArgs>>>(bargs)...});
 
        m_impl = Create<CallbackImpl<R, UArgs...>>(
            [f, bargs...](auto&&... uargs) -> R {
                return f(bargs..., std::forward<decltype(uargs)>(uargs)...);
            },
            components);
    }
 
    /**
     * Construct from a function and bind some arguments (if any)
     *
     * @tparam T \deduced The type of the function
     * @tparam BArgs \deduced The types of the bound arguments
     * @param [in] func The function
     * @param [in] bargs The values of the bound arguments
     *
     * @internal
     * We leverage SFINAE to have the compiler discard this constructor when the type
     * of the first argument is a class derived from CallbackBase (i.e., a Callback).
     */
    template <typename T,
              typename... BArgs,
              std::enable_if_t<!std::is_base_of_v<CallbackBase, T> &&
                                   std::is_invocable_r_v<R, T, BArgs..., UArgs...>,
                               int> = 0>
    Callback(T func, BArgs... bargs)
    {
        // store the function in a std::function object
        std::function<R(BArgs..., UArgs...)> f(func);
 
        // The original function is comparable if it is a function pointer or
        // a pointer to a member function or a pointer to a member data.
        constexpr bool isComp =
            std::is_function_v<std::remove_pointer_t<T>> || std::is_member_pointer_v<T>;
 
        CallbackComponentVector components(
            {std::make_shared<CallbackComponent<T, isComp>>(func),
             std::make_shared<CallbackComponent<std::decay_t<BArgs>>>(bargs)...});
 
        m_impl = Create<CallbackImpl<R, UArgs...>>(
            [f, bargs...](auto&&... uargs) -> R {
                return f(bargs..., std::forward<decltype(uargs)>(uargs)...);
            },
            components);
    }
 
  private:
    /**
     * Implementation of the Bind method
     *
     * @tparam BoundArgs The types of the arguments to bind
     * @param [in] seq A compile-time integer sequence
     * @param [in] bargs The values of the arguments to bind
     * @return The bound callback
     *
     * @internal
     * The integer sequence is 0..N-1, where N is the number of arguments left unbound.
     */
    template <std::size_t... INDEX, typename... BoundArgs>
    auto BindImpl(std::index_sequence<INDEX...> seq, BoundArgs&&... bargs)
    {
        Callback<R, std::tuple_element_t<sizeof...(bargs) + INDEX, std::tuple<UArgs...>>...> cb;
 
        const auto f = DoPeekImpl()->GetFunction();
 
        CallbackComponentVector components(DoPeekImpl()->GetComponents());
        components.insert(components.end(),
                          {std::make_shared<CallbackComponent<std::decay_t<BoundArgs>>>(bargs)...});
 
        cb.m_impl = Create<std::remove_pointer_t<decltype(cb.DoPeekImpl())>>(
            [f, bargs...](auto&&... uargs) mutable {
                return f(bargs..., std::forward<decltype(uargs)>(uargs)...);
            },
            components);
 
        return cb;
    }
 
  public:
    /**
     * Bind a variable number of arguments
     *
     * @tparam BoundArgs \deduced The types of the arguments to bind
     * @param [in] bargs The values of the arguments to bind
     * @return The bound callback
     */
    template <typename... BoundArgs>
    auto Bind(BoundArgs&&... bargs)
    {
        static_assert(sizeof...(UArgs) > 0);
        return BindImpl(std::make_index_sequence<sizeof...(UArgs) - sizeof...(BoundArgs)>{},
                        std::forward<BoundArgs>(bargs)...);
    }
 
    /**
     * Check for null implementation
     *
     * @return \c true if I don't have an implementation
     */
    bool IsNull() const
    {
        return (DoPeekImpl() == nullptr);
    }
 
    /** Discard the implementation, set it to null */
    void Nullify()
    {
        m_impl = nullptr;
    }
 
    /**
     * Functor with varying numbers of arguments
     *
     * @param uargs The arguments to the callback
     * @return Callback value
     */
    R operator()(UArgs... uargs) const
    {
        return (*(DoPeekImpl()))(uargs...);
    }
 
    /**
     * Equality test.
     *
     * @param [in] other Callback
     * @return \c true if we are equal
     */
    bool IsEqual(const CallbackBase& other) const
    {
        return m_impl->IsEqual(other.GetImpl());
    }
 
    /**
     * Check for compatible types
     *
     * @param [in] other Callback Ptr
     * @return \c true if other can be dynamic_cast to my type
     */
    bool CheckType(const CallbackBase& other) const
    {
        return DoCheckType(other.GetImpl());
    }
 
    /**
     * Adopt the other's implementation, if type compatible
     *
     * @param [in] other Callback
     * @returns \c true if \pname{other} was type-compatible and could be adopted.
     */
    bool Assign(const CallbackBase& other)
    {
        auto otherImpl = other.GetImpl();
        if (!DoCheckType(otherImpl))
        {
            std::string othTid = otherImpl->GetTypeid();
            std::string myTid = CallbackImpl<R, UArgs...>::DoGetTypeid();
            NS_FATAL_ERROR_CONT("Incompatible types. (feed to \"c++filt -t\" if needed)"
                                << std::endl
                                << "got=" << othTid << std::endl
                                << "expected=" << myTid);
            return false;
        }
        m_impl = const_cast<CallbackImplBase*>(PeekPointer(otherImpl));
        return true;
    }
 
  private:
    /** @return The pimpl pointer */
    CallbackImpl<R, UArgs...>* DoPeekImpl() const
    {
        return static_cast<CallbackImpl<R, UArgs...>*>(PeekPointer(m_impl));
    }
 
    /**
     * Check for compatible types
     *
     * @param [in] other Callback Ptr
     * @return \c true if other can be dynamic_cast to my type
     */
    bool DoCheckType(Ptr<const CallbackImplBase> other) const
    {
        if (!other)
        {
            return true;
        }
 
        return (dynamic_cast<const CallbackImpl<R, UArgs...>*>(PeekPointer(other)) != nullptr);
    }
};
 
/**
 * Inequality test.
 *
 * @tparam R \explicit The return type of the Callbacks
 * @tparam UArgs \explicit The types of any arguments to the Callbacks
 * @param [in] a Callback
 * @param [in] b Callback
 *
 * @return \c true if the Callbacks are not equal
 */
template <typename R, typename... Args>
bool
operator!=(Callback<R, Args...> a, Callback<R, Args...> b)
{
    return !a.IsEqual(b);
}
 
/**
 * @{
 */
/**
 * Build Callbacks for class method members which take varying numbers
 * of arguments and potentially returning a value.
 *
 * @tparam T   \deduced Type of the class having the member function.
 * @tparam OBJ \deduced Type of the class instance.
 * @tparam R   \deduced Return type of the callback.
 * @tparam Args \deduced Type list of any arguments to the member function.
 *
 * @param [in] memPtr Class method member pointer
 * @param [in] objPtr Class instance
 * @return A wrapper Callback
 *
 * Build Callbacks for class method members which take varying numbers of arguments
 * and potentially returning a value.
 */
template <typename T, typename OBJ, typename R, typename... Args>
Callback<R, Args...>
MakeCallback(R (T::*memPtr)(Args...), OBJ objPtr)
{
    return Callback<R, Args...>(memPtr, objPtr);
}
 
template <typename T, typename OBJ, typename R, typename... Args>
Callback<R, Args...>
MakeCallback(R (T::*memPtr)(Args...) const, OBJ objPtr)
{
    return Callback<R, Args...>(memPtr, objPtr);
}
 
/**@}*/
 
/**
 * @ingroup callback
 * @tparam R   \deduced Return type of the callback function..
 * @tparam Args  \deduced Type list of any arguments to the member function.
 * @param [in] fnPtr Function pointer
 * @return A wrapper Callback
 *
 * Build Callbacks for functions which take varying numbers of arguments
 * and potentially returning a value.
 */
template <typename R, typename... Args>
Callback<R, Args...>
MakeCallback(R (*fnPtr)(Args...))
{
    return Callback<R, Args...>(fnPtr);
}
 
/**
 * @ingroup callback
 * @tparam R   \deduced Return type of the callback function..
 * @tparam Args  \deduced Type list of any arguments to the member function.
 * @return A wrapper Callback
 *
 * Build null Callbacks which take no arguments,
 * for varying number of template arguments,
 * and potentially returning a value.
 */
template <typename R, typename... Args>
Callback<R, Args...>
MakeNullCallback()
{
    return Callback<R, Args...>();
}
 
/**
 * @ingroup makeboundcallback
 * @{
 * Make Callbacks with varying number of bound arguments.
 * @tparam R   \deduced Return type of the callback function..
 * @tparam Args \deduced Type list of any arguments to the member function.
 * @tparam BArgs \deduced Type list of bound arguments.
 * @param [in] fnPtr Function pointer
 * @param [in] bargs Bound arguments
 * @return A bound Callback
 */
template <typename R, typename... Args, typename... BArgs>
auto
MakeBoundCallback(R (*fnPtr)(Args...), BArgs&&... bargs)
{
    return Callback<R, Args...>(fnPtr).Bind(std::forward<BArgs>(bargs)...);
}
 
/**
 * @tparam T   \deduced Type of the class having the member function.
 * @tparam OBJ \deduced Type of the class instance.
 * @tparam R   \deduced Return type of the callback.
 * @tparam Args \deduced Type list of any arguments to the member function.
 * @tparam BArgs \deduced Type list of bound arguments.
 * @param [in] memPtr Class method member pointer
 * @param [in] objPtr Class instance
 * @param [in] bargs Bound arguments
 * @return A wrapper Callback
 *
 * Build Callbacks for class method members which take varying numbers of arguments
 * and potentially returning a value.
 */
template <typename T, typename OBJ, typename R, typename... Args, typename... BArgs>
auto
MakeCallback(R (T::*memPtr)(Args...), OBJ objPtr, BArgs... bargs)
{
    return Callback<R, Args...>(memPtr, objPtr).Bind(bargs...);
}
 
template <typename T, typename OBJ, typename R, typename... Args, typename... BArgs>
auto
MakeCallback(R (T::*memPtr)(Args...) const, OBJ objPtr, BArgs... bargs)
{
    return Callback<R, Args...>(memPtr, objPtr).Bind(bargs...);
}
 
/**@}*/
 
} // namespace ns3
 
namespace ns3
{
 
class CallbackValue : public AttributeValue
{
  public:
    CallbackValue();
    CallbackValue(const CallbackBase& value);
    ~CallbackValue() override;
    // Documented by print-introspected-doxygen.cc
    void Set(const CallbackBase& value);
    CallbackBase Get();
    template <typename T>
    bool GetAccessor(T& value) const;
    /** @return A copy of this CallBack */
    Ptr<AttributeValue> Copy() const override;
    /**
     * Serialize to string
     * @param [in] checker The checker to validate with
     * @return Serialized form of this Callback.
     */
    std::string SerializeToString(Ptr<const AttributeChecker> checker) const override;
    /**
     * Deserialize from string (not implemented)
     *
     * @param [in] value Source string
     * @param [in] checker Checker to validate with
     * @return \c true if successful
     */
    bool DeserializeFromString(std::string value, Ptr<const AttributeChecker> checker) override;
 
  private:
    /* Documented by print-introspected-doxygen.cc */
    CallbackBase m_value;
};
 
ATTRIBUTE_ACCESSOR_DEFINE(Callback);
ATTRIBUTE_CHECKER_DEFINE(Callback);
 
} // namespace ns3
 
namespace ns3
{
 
template <typename T>
bool
CallbackValue::GetAccessor(T& value) const
{
    if (value.CheckType(m_value))
    {
        if (!value.Assign(m_value))
        {
            NS_FATAL_ERROR_NO_MSG();
        }
        return true;
    }
    return false;
}
 
} // namespace ns3
 
#endif /* CALLBACK_H */