hazard_pointer.hpp

//
// Copyright (c) 2018-2020 Manuel Pöter.
// Licensed under the MIT License. See LICENSE file in the project root for full license information.
//
 
#ifndef XENIUM_HAZARD_POINTER_HPP
#define XENIUM_HAZARD_POINTER_HPP
 
#include <xenium/reclamation/detail/allocation_tracker.hpp>
#include <xenium/reclamation/detail/concurrent_ptr.hpp>
#include <xenium/reclamation/detail/deletable_object.hpp>
#include <xenium/reclamation/detail/guard_ptr.hpp>
#include <xenium/reclamation/detail/thread_block_list.hpp>
 
#include <xenium/acquire_guard.hpp>
#include <xenium/parameter.hpp>
#include <xenium/policy.hpp>
 
#include <memory>
#include <stdexcept>
 
namespace xenium::reclamation {
 
class bad_hazard_pointer_alloc : public std::runtime_error {
  using std::runtime_error::runtime_error;
};
 
namespace detail {
  template <class Strategy, class Derived>
  struct basic_hp_thread_control_block;
 
  template <size_t K_, size_t A, size_t B, template <class> class ThreadControlBlock>
  struct generic_hp_allocation_strategy {
    static constexpr size_t K = K_;
 
    static size_t retired_nodes_threshold() { return A * number_of_active_hazard_pointers() + B; }
 
    static size_t number_of_active_hazard_pointers() { return number_of_active_hps.load(std::memory_order_relaxed); }
 
    using thread_control_block = ThreadControlBlock<generic_hp_allocation_strategy>;
 
  private:
    friend thread_control_block;
    friend basic_hp_thread_control_block<generic_hp_allocation_strategy, thread_control_block>;
 
    inline static std::atomic<size_t> number_of_active_hps{0};
  };
 
  template <class Strategy>
  struct static_hp_thread_control_block;
 
  template <class Strategy>
  struct dynamic_hp_thread_control_block;
} // namespace detail
 
namespace hp_allocation {
  template <size_t K = 2, size_t A = 2, size_t B = 100>
  struct static_strategy : detail::generic_hp_allocation_strategy<K, A, B, detail::static_hp_thread_control_block> {};
 
  template <size_t K = 2, size_t A = 2, size_t B = 100>
  struct dynamic_strategy : detail::generic_hp_allocation_strategy<K, A, B, detail::dynamic_hp_thread_control_block> {};
} // namespace hp_allocation
 
template <class AllocationStrategy = hp_allocation::static_strategy<3>>
struct hazard_pointer_traits {
  using allocation_strategy = AllocationStrategy;
 
  template <class... Policies>
  using with =
    hazard_pointer_traits<parameter::type_param_t<policy::allocation_strategy, AllocationStrategy, Policies...>>;
};
 
template <typename Traits = hazard_pointer_traits<>>
class hazard_pointer {
  using allocation_strategy = typename Traits::allocation_strategy;
  using thread_control_block = typename allocation_strategy::thread_control_block;
  friend detail::basic_hp_thread_control_block<allocation_strategy, thread_control_block>;
 
  template <class T, class MarkedPtr>
  class guard_ptr;
 
public:
  template <class... Policies>
  using with = hazard_pointer<typename Traits::template with<Policies...>>;
 
  template <class T, std::size_t N = 0, class Deleter = std::default_delete<T>>
  class enable_concurrent_ptr;
 
  class region_guard {};
 
  template <class T, std::size_t N = T::number_of_mark_bits>
  using concurrent_ptr = detail::concurrent_ptr<T, N, guard_ptr>;
 
  ALLOCATION_TRACKER;
 
private:
  struct thread_data;
 
  inline static detail::thread_block_list<thread_control_block> global_thread_block_list;
  inline static thread_local thread_data local_thread_data;
 
  ALLOCATION_TRACKING_FUNCTIONS;
};
 
template <typename Traits>
template <class T, std::size_t N, class Deleter>
class hazard_pointer<Traits>::enable_concurrent_ptr :
    private detail::deletable_object_impl<T, Deleter>,
    private detail::tracked_object<hazard_pointer> {
public:
  static constexpr std::size_t number_of_mark_bits = N;
 
protected:
  enable_concurrent_ptr() noexcept = default;
  enable_concurrent_ptr(const enable_concurrent_ptr&) noexcept = default;
  enable_concurrent_ptr(enable_concurrent_ptr&&) noexcept = default;
  enable_concurrent_ptr& operator=(const enable_concurrent_ptr&) noexcept = default;
  enable_concurrent_ptr& operator=(enable_concurrent_ptr&&) noexcept = default;
  ~enable_concurrent_ptr() noexcept override = default;
 
private:
  friend detail::deletable_object_impl<T, Deleter>;
 
  template <class, class>
  friend class guard_ptr;
};
 
template <typename Traits>
template <class T, class MarkedPtr>
class hazard_pointer<Traits>::guard_ptr : public detail::guard_ptr<T, MarkedPtr, guard_ptr<T, MarkedPtr>> {
  using base = detail::guard_ptr<T, MarkedPtr, guard_ptr>;
  using Deleter = typename T::Deleter;
 
public:
  guard_ptr() noexcept = default;
 
  // Guard a marked ptr.
  explicit guard_ptr(const MarkedPtr& p);
  guard_ptr(const guard_ptr& p);
  guard_ptr(guard_ptr&& p) noexcept;
 
  guard_ptr& operator=(const guard_ptr& p);
  guard_ptr& operator=(guard_ptr&& p) noexcept;
 
  // Atomically take snapshot of p, and *if* it points to unreclaimed object, acquire shared ownership of it.
  void acquire(const concurrent_ptr<T>& p, std::memory_order order = std::memory_order_seq_cst);
 
  // Like acquire, but quit early if a snapshot != expected.
  bool acquire_if_equal(const concurrent_ptr<T>& p,
                        const MarkedPtr& expected,
                        std::memory_order order = std::memory_order_seq_cst);
 
  // Release ownership. Postcondition: get() == nullptr.
  void reset() noexcept;
 
  // Reset. Deleter d will be applied some time after all owners release their ownership.
  void reclaim(Deleter d = Deleter()) noexcept;
 
private:
  using enable_concurrent_ptr = hazard_pointer::enable_concurrent_ptr<T, MarkedPtr::number_of_mark_bits, Deleter>;
 
  friend base;
  void do_swap(guard_ptr& g) noexcept;
 
  typename thread_control_block::hazard_pointer* hp = nullptr;
};
} // namespace xenium::reclamation
 
#define HAZARD_POINTER_IMPL
#include <xenium/reclamation/impl/hazard_pointer.hpp>
#undef HAZARD_POINTER_IMPL
 
#endif