lock_free_pool.h

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/** @file storage/temptable/include/temptable/lock_free_pool.h
Lock-free pool implementation. */
 
#ifndef TEMPTABLE_LOCK_FREE_POOL_H
#define TEMPTABLE_LOCK_FREE_POOL_H
 
#include <array>
 
#include "storage/temptable/include/temptable/lock_free_type.h"
 
namespace temptable {
 
/** Lock-free pool which consists of POOL_SIZE Lock_free_type elements. It has
 * all the guarantees and properties of Lock_free_type and its consisting pieces
 * so for more details please consult the documentation of those. E.g. user code
 * can opt-in for different alignment-requirements and/or lock-free type
 * selection algorithms. This type is envisioned to be used as a building block
 * for higher-abstraction (lock-free) ADTs.
 * */
template <typename T, size_t POOL_SIZE,
          Alignment ALIGNMENT = Alignment::NATURAL,
          template <typename, typename = void> class TypeSelector =
              Lock_free_type_selector>
class Lock_free_pool {
  std::array<Lock_free_type<T, ALIGNMENT, TypeSelector>, POOL_SIZE> m_lock_free;
 
 public:
  using Type = typename Lock_free_type<T, ALIGNMENT, TypeSelector>::Type;
 
  /** Default constructor. Uses value-initialization to initialize underlying
   * T's.*/
  Lock_free_pool() : m_lock_free() {}
 
  /** Constructor. Uses explicit value to initialize underlying T's. */
  Lock_free_pool(Lock_free_pool::Type default_value) {
    for (auto &v : m_lock_free) v.m_value = default_value;
  }
 
  /** Copy-constructor and copy-assignment operator are disabled. */
  Lock_free_pool(const Lock_free_pool &) = delete;
  Lock_free_pool &operator=(const Lock_free_pool &) = delete;
 
  /** Ditto for move-constructor and move-assignment operator. */
  Lock_free_pool(Lock_free_pool &&) = delete;
  Lock_free_pool &operator=(Lock_free_pool &&) = delete;
 
  /** Atomically replaces current value in an array at given index.
   *
   * [in] idx Index of an element whose value is to be replaced.
   * [in] value Value to store into the atomic variable.
   * [in] order Memory order constraints to enforce.
   * */
  void store(size_t idx, Lock_free_pool::Type value,
             std::memory_order order = std::memory_order_seq_cst) {
    m_lock_free[idx].m_value.store(value, order);
  }
 
  /** Atomically loads and returns the current value from an array at given
   * index.
   *
   * [in] idx Index of an element whose value is to be returned.
   * [in] order Memory order constraints to enforce.
   * @return Returns the current value from given index.
   * */
  Lock_free_pool::Type load(
      size_t idx, std::memory_order order = std::memory_order_seq_cst) const {
    return m_lock_free[idx].m_value.load(order);
  }
 
  /** Atomically compares the object representation of an array element at given
   *  index with the expected, and if those are bitwise-equal, replaces the
   * former with desired.
   *
   * [in] idx Index of an element whose value is to be compared against.
   * [in] expected Value expected to be found in the atomic object. Gets stored
   * with the actual value of *this if the comparison fails.
   * [in] desired Value to store in the atomic object if it is as expected.
   * [in] order Memory order constraints to enforce.
   * @return True if the underlying atomic value was successfully changed, false
   * otherwise.
   * */
  bool compare_exchange_strong(
      size_t idx, Lock_free_pool::Type &expected, Lock_free_pool::Type desired,
      std::memory_order order = std::memory_order_seq_cst) {
    return m_lock_free[idx].m_value.compare_exchange_strong(expected, desired,
                                                            order);
  }
 
  /** Returns the number of elements this pool contains.
   *
   * @return Number of elements in the pool.
   * */
  constexpr size_t size() const { return POOL_SIZE; }
};
 
}  // namespace temptable
 
#endif /* TEMPTABLE_LOCK_FREE_POOL_H */