/******************************************************************************
 *                       ____    _    _____                                   *
 *                      / ___|  / \  |  ___|    C++                           *
 *                     | |     / _ \ | |_       Actor                         *
 *                     | |___ / ___ \|  _|      Framework                     *
 *                      \____/_/   \_|_|                                      *
 *                                                                            *
 * Copyright 2011-2018 Dominik Charousset                                     *
 *                                                                            *
 * Distributed under the terms and conditions of the BSD 3-Clause License or  *
 * (at your option) under the terms and conditions of the Boost Software      *
 * License 1.0. See accompanying files LICENSE and LICENSE_ALTERNATIVE.       *
 *                                                                            *
 * If you did not receive a copy of the license files, see                    *
 * http://opensource.org/licenses/BSD-3-Clause and                            *
 * http://www.boost.org/LICENSE_1_0.txt.                                      *
 ******************************************************************************/

#ifndef CAF_ACTOR_STORAGE_HPP
#define CAF_ACTOR_STORAGE_HPP

#include <new>
#include <atomic>
#include <cstddef>
#include <type_traits>

#include "caf/config.hpp"
#include "caf/abstract_actor.hpp"
#include "caf/actor_control_block.hpp"

#ifdef CAF_GCC
#pragma GCC diagnostic push
#pragma GCC diagnostic ignored "-Winvalid-offsetof"
#endif

namespace caf {

template <class T>
class actor_storage {
public:
  template <class... Us>
  actor_storage(actor_id x, node_id y, actor_system* sys, Us&&... zs)
      : ctrl(x, y, sys, data_dtor, block_dtor) {
    // construct data member
    new (&data) T(std::forward<Us>(zs)...);
  }

  ~actor_storage() {
    // 1) make sure control block fits into a single cache line
    static_assert(sizeof(actor_control_block) < CAF_CACHE_LINE_SIZE,
                  "actor_control_block exceeds a single cache line");
    // Clang in combination with libc++ on Linux complains about offsetof:
    //     error: 'actor_storage' does not refer to a value
    // Until we have found a reliable solution, we disable this safety check.
    #if !(defined(CAF_CLANG) && defined(CAF_LINUX))
    // 2) make sure reinterpret cast of the control block to the storage works
    static_assert(offsetof(actor_storage, ctrl) == 0,
                  "control block is not at the start of the storage");
    // 3) make sure we can obtain a data pointer by jumping one cache line
    static_assert(offsetof(actor_storage, data) == CAF_CACHE_LINE_SIZE,
                  "data is not at cache line size boundary");
    #else
    // 4) make sure static_cast and reinterpret_cast
    //    between T* and abstract_actor* are identical
    constexpr abstract_actor* dummy = nullptr;
    constexpr T* derived_dummy = static_cast<T*>(dummy);
    static_assert(derived_dummy == nullptr,
                  "actor subtype has illegal memory alignment "
                  "(probably due to virtual inheritance)");
    #endif
  }

  actor_storage(const actor_storage&) = delete;
  actor_storage& operator=(const actor_storage&) = delete;

  static_assert(sizeof(actor_control_block) < CAF_CACHE_LINE_SIZE,
                "actor_control_block exceeds 64 bytes");

  actor_control_block ctrl;
  char pad[CAF_CACHE_LINE_SIZE - sizeof(actor_control_block)];
  union { T data; };

private:
  static void data_dtor(abstract_actor* ptr) {
    // safe due to static assert #3
    ptr->on_destroy();
    static_cast<T*>(ptr)->~T();
  }

  static void block_dtor(actor_control_block* ptr) {
    // safe due to static assert #2
    delete reinterpret_cast<actor_storage*>(ptr);
  }
};

/// @relates actor_storage
template <class T>
bool intrusive_ptr_upgrade_weak(actor_storage<T>* x) {
  auto count = x->ctrl.strong_refs.load();
  while (count != 0) {
    if (x->ctrl.strong_refs.compare_exchange_weak(count, count + 1,
                                                  std::memory_order_relaxed))
      return true;
  }
  return false;
}

/// @relates actor_storage
template <class T>
void intrusive_ptr_add_weak_ref(actor_storage<T>* x) {
  x->ctrl.weak_refs.fetch_add(1, std::memory_order_relaxed);
}

/// @relates actor_storage
template <class T>
void intrusive_ptr_release_weak(actor_storage<T>* x) {
  // destroy object if last weak pointer expires
  if (x->ctrl.weak_refs == 1
      || x->ctrl.weak_refs.fetch_sub(1, std::memory_order_acq_rel) == 1)
    delete x;
}

/// @relates actor_storage
template <class T>
void intrusive_ptr_add_ref(actor_storage<T>* x) {
  x->ctrl.strong_refs.fetch_add(1, std::memory_order_relaxed);
}

/// @relates actor_storage
template <class T>
void intrusive_ptr_release(actor_storage<T>* x) {
  // release implicit weak pointer if the last strong ref expires
  // and destroy the data block
  if (x->ctrl.strong_refs.fetch_sub(1, std::memory_order_acq_rel) == 1) {
    x->destroy_data();
    intrusive_ptr_relase_weak(x);
  }
}

} // namespace caf

#ifdef CAF_GCC
#pragma GCC diagnostic pop
#endif

#endif // CAF_ACTOR_STORAGE_HPP
