srsLTE/lib/include/srslte/common/task.h

/*
 * Copyright 2013-2020 Software Radio Systems Limited
 *
 * This file is part of srsLTE.
 *
 * srsLTE is free software: you can redistribute it and/or modify
 * it under the terms of the GNU Affero General Public License as
 * published by the Free Software Foundation, either version 3 of
 * the License, or (at your option) any later version.
 *
 * srsLTE is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU Affero General Public License for more details.
 *
 * A copy of the GNU Affero General Public License can be found in
 * the LICENSE file in the top-level directory of this distribution
 * and at http://www.gnu.org/licenses/.
 *
 */

#ifndef SRSLTE_TASK_H
#define SRSLTE_TASK_H

#include <cstddef>
#include <functional>
#include <type_traits>

namespace srslte {

constexpr size_t default_buffer_size = 32;

template <class Signature, size_t Capacity = default_buffer_size>
class inplace_task;

namespace task_details {

template <typename R, typename... Args>
struct oper_table_t {
  using call_oper_t = R (*)(void* src, Args&&... args);
  using move_oper_t = void (*)(void* src, void* dest);
  using dtor_oper_t = void (*)(void* src);

  const static oper_table_t* get_empty() noexcept
  {
    const static oper_table_t t{true,
                                [](void* src, Args&&... args) -> R { throw std::bad_function_call(); },
                                [](void*, void*) {},
                                [](void*) {}};
    return &t;
  }

  template <typename Func>
  const static oper_table_t* get_small() noexcept
  {
    const static oper_table_t t{
        true,
        [](void* src, Args&&... args) -> R { return (*static_cast<Func*>(src))(std::forward<Args>(args)...); },
        [](void* src, void* dest) -> void {
          ::new (dest) Func{std::move(*static_cast<Func*>(src))};
          static_cast<Func*>(src)->~Func();
        },
        [](void* src) -> void { static_cast<Func*>(src)->~Func(); }};
    return &t;
  }

  template <typename Func>
  const static oper_table_t* get_big() noexcept
  {
    const static oper_table_t t{
        false,
        [](void* src, Args&&... args) -> R { return (*static_cast<Func*>(src))(std::forward<Args>(args)...); },
        [](void* src, void* dest) -> void {
          *static_cast<Func**>(dest) = *static_cast<Func**>(src);
          *static_cast<Func**>(src)  = nullptr;
        },
        [](void* src) -> void { static_cast<Func*>(src)->~Func(); }};
    return &t;
  }

  oper_table_t(const oper_table_t&) = delete;
  oper_table_t(oper_table_t&&)      = delete;
  oper_table_t& operator=(const oper_table_t&) = delete;
  oper_table_t& operator=(oper_table_t&&) = delete;
  ~oper_table_t()                         = default;

  bool        is_in_buffer;
  call_oper_t call;
  move_oper_t move;
  dtor_oper_t dtor;

private:
  oper_table_t() = default;
  oper_table_t(bool is_in_buffer_, call_oper_t call_, move_oper_t move_, dtor_oper_t dtor_) :
    is_in_buffer(is_in_buffer_),
    call(call_),
    move(move_),
    dtor(dtor_)
  {}
};

template <class>
struct is_inplace_task : std::false_type {};
template <class Sig, size_t Capacity>
struct is_inplace_task<inplace_task<Sig, Capacity> > : std::true_type {};

} // namespace task_details

template <class R, class... Args, size_t Capacity>
class inplace_task<R(Args...), Capacity>
{
  static constexpr size_t capacity = Capacity >= sizeof(void*) ? Capacity : sizeof(void*);
  using storage_t                  = typename std::aligned_storage<capacity, alignof(std::max_align_t)>::type;
  using oper_table_t               = task_details::oper_table_t<R, Args...>;

public:
  inplace_task() noexcept { oper_ptr = oper_table_t::get_empty(); }

  template <typename T,
            typename FunT = typename std::decay<T>::type,
            typename      = typename std::enable_if<sizeof(FunT) <= capacity>::type,
            typename      = typename std::enable_if<not task_details::is_inplace_task<FunT>::value>::type>
  inplace_task(T&& function)
  {
    oper_ptr = oper_table_t::template get_small<FunT>();
    ::new (&buffer) FunT{std::forward<T>(function)};
  }

  template <typename T,
            typename FunT = typename std::decay<T>::type,
            typename      = typename std::enable_if<not task_details::is_inplace_task<FunT>::value and
                                               (sizeof(FunT) > capacity)>::type>
  inplace_task(T&& function)
  {
    oper_ptr = oper_table_t::template get_big<FunT>();
    ptr      = static_cast<void*>(new FunT{std::forward<T>(function)});
  }

  inplace_task(inplace_task&& other) noexcept
  {
    oper_ptr       = other.oper_ptr;
    other.oper_ptr = oper_table_t::get_empty();
    if (oper_ptr->is_in_buffer) {
      oper_ptr->move(&other.buffer, &buffer);
    } else {
      oper_ptr->move(&other.ptr, &ptr);
    }
  }

  ~inplace_task() { oper_ptr->dtor(get_buffer()); }

  inplace_task& operator=(inplace_task&& other) noexcept
  {
    oper_ptr->dtor(get_buffer());
    oper_ptr       = other.oper_ptr;
    other.oper_ptr = oper_table_t::get_empty();
    if (oper_ptr->is_in_buffer) {
      oper_ptr->move(&other.buffer, &buffer);
    } else {
      oper_ptr->move(&other.ptr, &ptr);
    }
    return *this;
  }

  R operator()(Args&&... args) { return oper_ptr->call(get_buffer(), std::forward<Args>(args)...); }

  bool is_empty() const { return oper_ptr == oper_table_t::get_empty(); }
  bool is_in_small_buffer() const { return oper_ptr->is_in_buffer; }

  void swap(inplace_task& other) noexcept
  {
    if (this == &other)
      return;

    if (oper_ptr->is_in_buffer and other.oper_ptr->is_in_buffer) {
      storage_t tmp;
      oper_ptr->move(&buffer, &tmp);
      other.oper_ptr->move(&other.buffer, &buffer);
      oper_ptr->move(&tmp, &other.buffer);
    } else if (oper_ptr->is_in_buffer and not other.oper_ptr->is_in_buffer) {
      void* tmpptr = other.ptr;
      oper_ptr->move(&buffer, &other.buffer);
      ptr = tmpptr;
    } else if (not oper_ptr->is_in_buffer and other.oper_ptr->is_in_buffer) {
      void* tmpptr = ptr;
      other.oper_ptr->move(&other.buffer, &buffer);
      oper_ptr->move(&tmpptr, &other.ptr);
    } else {
      std::swap(ptr, other.ptr);
    }
    std::swap(oper_ptr, other.oper_ptr);
  }

  friend void swap(inplace_task& lhs, inplace_task& rhs) noexcept { lhs.swap(rhs); }

private:
  union {
    storage_t buffer;
    void*     ptr;
  };
  const oper_table_t* oper_ptr;

  void* get_buffer() { return oper_ptr->is_in_buffer ? &buffer : ptr; }
};

} // namespace srslte

#endif // SRSLTE_TASK_H