Kokkos_UnorderedMap.hpp

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//@HEADER
// ************************************************************************
//
//                        Kokkos v. 4.0
//       Copyright (2022) National Technology & Engineering
//               Solutions of Sandia, LLC (NTESS).
//
// Under the terms of Contract DE-NA0003525 with NTESS,
// the U.S. Government retains certain rights in this software.
//
// Part of Kokkos, under the Apache License v2.0 with LLVM Exceptions.
// See https://kokkos.org/LICENSE for license information.
// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
//
//@HEADER

 
#ifndef KOKKOS_UNORDERED_MAP_HPP
#define KOKKOS_UNORDERED_MAP_HPP
#ifndef KOKKOS_IMPL_PUBLIC_INCLUDE
#define KOKKOS_IMPL_PUBLIC_INCLUDE
#define KOKKOS_IMPL_PUBLIC_INCLUDE_NOTDEFINED_UNORDEREDMAP
#endif
 
#include <Kokkos_Core.hpp>
#include <Kokkos_Functional.hpp>
 
#include <Kokkos_Bitset.hpp>
 
#include <impl/Kokkos_Traits.hpp>
#include <impl/Kokkos_UnorderedMap_impl.hpp>
 
#include <iostream>
 
#include <cstdint>
 
namespace Kokkos {
 
enum : unsigned { UnorderedMapInvalidIndex = ~0u };

 
class UnorderedMapInsertResult {
 private:
  enum Status : uint32_t {
    SUCCESS          = 1u << 31,
    EXISTING         = 1u << 30,
    FREED_EXISTING   = 1u << 29,
    LIST_LENGTH_MASK = ~(SUCCESS | EXISTING | FREED_EXISTING)
  };
 
 public:
  KOKKOS_FORCEINLINE_FUNCTION
  bool success() const { return (m_status & SUCCESS); }

  KOKKOS_FORCEINLINE_FUNCTION
  bool existing() const { return (m_status & EXISTING); }

  KOKKOS_FORCEINLINE_FUNCTION
  bool failed() const { return m_index == UnorderedMapInvalidIndex; }

  KOKKOS_FORCEINLINE_FUNCTION
  bool freed_existing() const { return (m_status & FREED_EXISTING); }

  KOKKOS_FORCEINLINE_FUNCTION
  uint32_t list_position() const { return (m_status & LIST_LENGTH_MASK); }

  KOKKOS_FORCEINLINE_FUNCTION
  uint32_t index() const { return m_index; }
 
  KOKKOS_FORCEINLINE_FUNCTION
  UnorderedMapInsertResult() : m_index(UnorderedMapInvalidIndex), m_status(0) {}
 
  KOKKOS_FORCEINLINE_FUNCTION
  void increment_list_position() {
    m_status += (list_position() < LIST_LENGTH_MASK) ? 1u : 0u;
  }
 
  KOKKOS_FORCEINLINE_FUNCTION
  void set_existing(uint32_t i, bool arg_freed_existing) {
    m_index = i;
    m_status =
        EXISTING | (arg_freed_existing ? FREED_EXISTING : 0u) | list_position();
  }
 
  KOKKOS_FORCEINLINE_FUNCTION
  void set_success(uint32_t i) {
    m_index  = i;
    m_status = SUCCESS | list_position();
  }
 
 private:
  uint32_t m_index;
  uint32_t m_status;
};

template <class ValueTypeView, class ValuesIdxType>
struct UnorderedMapInsertOpTypes {
  using value_type = typename ValueTypeView::non_const_value_type;
  struct NoOp {
    KOKKOS_FUNCTION
    void op(ValueTypeView, ValuesIdxType, const value_type) const {}
  };
  struct AtomicAdd {
    KOKKOS_FUNCTION
    void op(ValueTypeView values, ValuesIdxType values_idx,
            const value_type v) const {
      Kokkos::atomic_add(values.data() + values_idx, v);
    }
  };
};

template <typename Key, typename Value,
          typename Device  = Kokkos::DefaultExecutionSpace,
          typename Hasher  = pod_hash<std::remove_const_t<Key>>,
          typename EqualTo = pod_equal_to<std::remove_const_t<Key>>>
class UnorderedMap {
 private:
  using host_mirror_space =
      typename ViewTraits<Key, Device, void, void>::host_mirror_space;
 
 public:

  // key_types
  using declared_key_type = Key;
  using key_type          = std::remove_const_t<declared_key_type>;
  using const_key_type    = std::add_const_t<key_type>;
 
  // value_types
  using declared_value_type = Value;
  using value_type          = std::remove_const_t<declared_value_type>;
  using const_value_type    = std::add_const_t<value_type>;
 
  using device_type     = Device;
  using execution_space = typename Device::execution_space;
  using hasher_type     = Hasher;
  using equal_to_type   = EqualTo;
  using size_type       = uint32_t;
 
  // map_types
  using declared_map_type =
      UnorderedMap<declared_key_type, declared_value_type, device_type,
                   hasher_type, equal_to_type>;
  using insertable_map_type = UnorderedMap<key_type, value_type, device_type,
                                           hasher_type, equal_to_type>;
  using modifiable_map_type =
      UnorderedMap<const_key_type, value_type, device_type, hasher_type,
                   equal_to_type>;
  using const_map_type = UnorderedMap<const_key_type, const_value_type,
                                      device_type, hasher_type, equal_to_type>;
 
  static const bool is_set = std::is_void<value_type>::value;
  static const bool has_const_key =
      std::is_same<const_key_type, declared_key_type>::value;
  static const bool has_const_value =
      is_set || std::is_same<const_value_type, declared_value_type>::value;
 
  static const bool is_insertable_map =
      !has_const_key && (is_set || !has_const_value);
  static const bool is_modifiable_map = has_const_key && !has_const_value;
  static const bool is_const_map      = has_const_key && has_const_value;
 
  using insert_result = UnorderedMapInsertResult;
 
  using HostMirror =
      UnorderedMap<Key, Value, host_mirror_space, Hasher, EqualTo>;
 
  using histogram_type = Impl::UnorderedMapHistogram<const_map_type>;
 
 private:
  enum : size_type { invalid_index = ~static_cast<size_type>(0) };
 
  using impl_value_type = std::conditional_t<is_set, int, declared_value_type>;
 
  using key_type_view = std::conditional_t<
      is_insertable_map, View<key_type *, device_type>,
      View<const key_type *, device_type, MemoryTraits<RandomAccess>>>;
 
  using value_type_view = std::conditional_t<
      is_insertable_map || is_modifiable_map,
      View<impl_value_type *, device_type>,
      View<const impl_value_type *, device_type, MemoryTraits<RandomAccess>>>;
 
  using size_type_view = std::conditional_t<
      is_insertable_map, View<size_type *, device_type>,
      View<const size_type *, device_type, MemoryTraits<RandomAccess>>>;
 
  using bitset_type = std::conditional_t<is_insertable_map, Bitset<Device>,
                                         ConstBitset<Device>>;
 
  enum { modified_idx = 0, erasable_idx = 1, failed_insert_idx = 2 };
  enum { num_scalars = 3 };
  using scalars_view = View<int[num_scalars], LayoutLeft, device_type>;
 
 public:

  using default_op_type =
      typename UnorderedMapInsertOpTypes<value_type_view, uint32_t>::NoOp;

  UnorderedMap(size_type capacity_hint = 0, hasher_type hasher = hasher_type(),
               equal_to_type equal_to = equal_to_type())
      : m_bounded_insert(true),
        m_hasher(hasher),
        m_equal_to(equal_to),
        m_size("UnorderedMap size"),
        m_available_indexes(calculate_capacity(capacity_hint)),
        m_hash_lists(view_alloc(WithoutInitializing, "UnorderedMap hash list"),
                     Impl::find_hash_size(capacity())),
        m_next_index(view_alloc(WithoutInitializing, "UnorderedMap next index"),
                     capacity() + 1)  // +1 so that the *_at functions can
                                      // always return a valid reference
        ,
        m_keys("UnorderedMap keys", capacity()),
        m_values("UnorderedMap values", (is_set ? 0 : capacity())),
        m_scalars("UnorderedMap scalars") {
    if (!is_insertable_map) {
      Kokkos::Impl::throw_runtime_exception(
          "Cannot construct a non-insertable (i.e. const key_type) "
          "unordered_map");
    }
 
    Kokkos::deep_copy(m_hash_lists, invalid_index);
    Kokkos::deep_copy(m_next_index, invalid_index);
  }
 
  void reset_failed_insert_flag() { reset_flag(failed_insert_idx); }
 
  histogram_type get_histogram() { return histogram_type(*this); }

  void clear() {
    m_bounded_insert = true;
 
    if (capacity() == 0) return;
 
    m_available_indexes.clear();
 
    Kokkos::deep_copy(m_hash_lists, invalid_index);
    Kokkos::deep_copy(m_next_index, invalid_index);
    {
      const key_type tmp = key_type();
      Kokkos::deep_copy(m_keys, tmp);
    }
    Kokkos::deep_copy(m_scalars, 0);
    m_size() = 0;
  }
 
  KOKKOS_INLINE_FUNCTION constexpr bool is_allocated() const {
    return (m_keys.is_allocated() && (is_set || m_values.is_allocated()) &&
            m_scalars.is_allocated());
  }

  bool rehash(size_type requested_capacity = 0) {
    const bool bounded_insert = (capacity() == 0) || (size() == 0u);
    return rehash(requested_capacity, bounded_insert);
  }
 
  bool rehash(size_type requested_capacity, bool bounded_insert) {
    if (!is_insertable_map) return false;
 
    const size_type curr_size = size();
    requested_capacity =
        (requested_capacity < curr_size) ? curr_size : requested_capacity;
 
    insertable_map_type tmp(requested_capacity, m_hasher, m_equal_to);
 
    if (curr_size) {
      tmp.m_bounded_insert = false;
      Impl::UnorderedMapRehash<insertable_map_type> f(tmp, *this);
      f.apply();
    }
    tmp.m_bounded_insert = bounded_insert;
 
    *this = tmp;
 
    return true;
  }

  size_type size() const {
    if (capacity() == 0u) return 0u;
    if (modified()) {
      m_size() = m_available_indexes.count();
      reset_flag(modified_idx);
    }
    return m_size();
  }

  bool failed_insert() const { return get_flag(failed_insert_idx); }
 
  bool erasable() const {
    return is_insertable_map ? get_flag(erasable_idx) : false;
  }
 
  bool begin_erase() {
    bool result = !erasable();
    if (is_insertable_map && result) {
      execution_space().fence(
          "Kokkos::UnorderedMap::begin_erase: fence before setting erasable "
          "flag");
      set_flag(erasable_idx);
    }
    return result;
  }
 
  bool end_erase() {
    bool result = erasable();
    if (is_insertable_map && result) {
      execution_space().fence(
          "Kokkos::UnorderedMap::end_erase: fence before erasing");
      Impl::UnorderedMapErase<declared_map_type> f(*this);
      f.apply();
      execution_space().fence(
          "Kokkos::UnorderedMap::end_erase: fence after erasing");
      reset_flag(erasable_idx);
    }
    return result;
  }

  KOKKOS_FORCEINLINE_FUNCTION
  size_type capacity() const { return m_available_indexes.size(); }

  KOKKOS_INLINE_FUNCTION
  size_type hash_capacity() const { return m_hash_lists.extent(0); }
 
  //---------------------------------------------------------------------------
  //---------------------------------------------------------------------------

  template <typename InsertOpType = default_op_type>
  KOKKOS_INLINE_FUNCTION insert_result
  insert(key_type const &k, impl_value_type const &v = impl_value_type(),
         [[maybe_unused]] InsertOpType arg_insert_op = InsertOpType()) const {
    if constexpr (is_set) {
      static_assert(std::is_same_v<InsertOpType, default_op_type>,
                    "Insert Operations are not supported on sets.");
    }
 
    insert_result result;
 
    if (!is_insertable_map || capacity() == 0u ||
        m_scalars((int)erasable_idx)) {
      return result;
    }
 
    if (!m_scalars((int)modified_idx)) {
      m_scalars((int)modified_idx) = true;
    }
 
    int volatile &failed_insert_ref = m_scalars((int)failed_insert_idx);
 
    const size_type hash_value = m_hasher(k);
    const size_type hash_list  = hash_value % m_hash_lists.extent(0);
 
    size_type *curr_ptr = &m_hash_lists[hash_list];
    size_type new_index = invalid_index;
 
    // Force integer multiply to long
    size_type index_hint = static_cast<size_type>(
        (static_cast<double>(hash_list) * capacity()) / m_hash_lists.extent(0));
 
    size_type find_attempts = 0;
 
    enum : unsigned { bounded_find_attempts = 32u };
    const size_type max_attempts =
        (m_bounded_insert &&
         (bounded_find_attempts < m_available_indexes.max_hint()))
            ? bounded_find_attempts
            : m_available_indexes.max_hint();
 
    bool not_done = true;
 
#if defined(__MIC__)
#pragma noprefetch
#endif
    while (not_done) {
      // Continue searching the unordered list for this key,
      // list will only be appended during insert phase.
      // Need volatile_load as other threads may be appending.
 
      // FIXME_SYCL replacement for memory_fence
#ifdef KOKKOS_ENABLE_SYCL
      size_type curr = Kokkos::atomic_load(curr_ptr);
#else
      size_type curr = volatile_load(curr_ptr);
#endif
 
      KOKKOS_NONTEMPORAL_PREFETCH_LOAD(
          &m_keys[curr != invalid_index ? curr : 0]);
#if defined(__MIC__)
#pragma noprefetch
#endif
      while (curr != invalid_index && !m_equal_to(
#ifdef KOKKOS_ENABLE_SYCL
                                          Kokkos::atomic_load(&m_keys[curr])
#else
                                          volatile_load(&m_keys[curr])
#endif
                                              ,
                                          k)) {
        result.increment_list_position();
        index_hint = curr;
        curr_ptr   = &m_next_index[curr];
#ifdef KOKKOS_ENABLE_SYCL
        curr = Kokkos::atomic_load(curr_ptr);
#else
        curr = volatile_load(curr_ptr);
#endif
        KOKKOS_NONTEMPORAL_PREFETCH_LOAD(
            &m_keys[curr != invalid_index ? curr : 0]);
      }
 
      //------------------------------------------------------------
      // If key already present then return that index.
      if (curr != invalid_index) {
        const bool free_existing = new_index != invalid_index;
        if (free_existing) {
          // Previously claimed an unused entry that was not inserted.
          // Release this unused entry immediately.
          if (!m_available_indexes.reset(new_index)) {
            KOKKOS_IMPL_DO_NOT_USE_PRINTF("Unable to free existing\n");
          }
        }
 
        result.set_existing(curr, free_existing);
        if constexpr (!is_set) {
          arg_insert_op.op(m_values, curr, v);
        }
        not_done = false;
      }
      //------------------------------------------------------------
      // Key is not currently in the map.
      // If the thread has claimed an entry try to insert now.
      else {
        //------------------------------------------------------------
        // If have not already claimed an unused entry then do so now.
        if (new_index == invalid_index) {
          bool found = false;
          // use the hash_list as the flag for the search direction
          Kokkos::tie(found, index_hint) =
              m_available_indexes.find_any_unset_near(index_hint, hash_list);
 
          // found and index and this thread set it
          if (!found && ++find_attempts >= max_attempts) {
            failed_insert_ref = true;
            not_done          = false;
          } else if (m_available_indexes.set(index_hint)) {
            new_index = index_hint;
            // Set key and value
            KOKKOS_NONTEMPORAL_PREFETCH_STORE(&m_keys[new_index]);
// FIXME_SYCL replacement for memory_fence
#ifdef KOKKOS_ENABLE_SYCL
            Kokkos::atomic_store(&m_keys[new_index], k);
#else
            m_keys[new_index] = k;
#endif
 
            if (!is_set) {
              KOKKOS_NONTEMPORAL_PREFETCH_STORE(&m_values[new_index]);
#ifdef KOKKOS_ENABLE_SYCL
              Kokkos::atomic_store(&m_values[new_index], v);
#else
              m_values[new_index] = v;
#endif
            }
 
#ifndef KOKKOS_ENABLE_SYCL
            // Do not proceed until key and value are updated in global memory
            memory_fence();
#endif
          }
        } else if (failed_insert_ref) {
          not_done = false;
        }
 
        // Attempt to append claimed entry into the list.
        // Another thread may also be trying to append the same list so protect
        // with atomic.
        if (new_index != invalid_index &&
            curr == atomic_compare_exchange(
                        curr_ptr, static_cast<size_type>(invalid_index),
                        new_index)) {
          // Succeeded in appending
          result.set_success(new_index);
          not_done = false;
        }
      }
    }  // while ( not_done )
 
    return result;
  }
 
  KOKKOS_INLINE_FUNCTION
  bool erase(key_type const &k) const {
    bool result = false;
 
    if (is_insertable_map && 0u < capacity() && m_scalars((int)erasable_idx)) {
      if (!m_scalars((int)modified_idx)) {
        m_scalars((int)modified_idx) = true;
      }
 
      size_type index = find(k);
      if (valid_at(index)) {
        m_available_indexes.reset(index);
        result = true;
      }
    }
 
    return result;
  }

  KOKKOS_INLINE_FUNCTION
  size_type find(const key_type &k) const {
    size_type curr = 0u < capacity()
                         ? m_hash_lists(m_hasher(k) % m_hash_lists.extent(0))
                         : invalid_index;
 
    KOKKOS_NONTEMPORAL_PREFETCH_LOAD(&m_keys[curr != invalid_index ? curr : 0]);
    while (curr != invalid_index && !m_equal_to(m_keys[curr], k)) {
      KOKKOS_NONTEMPORAL_PREFETCH_LOAD(
          &m_keys[curr != invalid_index ? curr : 0]);
      curr = m_next_index[curr];
    }
 
    return curr;
  }

  KOKKOS_INLINE_FUNCTION
  bool exists(const key_type &k) const { return valid_at(find(k)); }

  template <typename Dummy = value_type>
  KOKKOS_FORCEINLINE_FUNCTION std::enable_if_t<
      !std::is_void<Dummy>::value,  // !is_set
      std::conditional_t<has_const_value, impl_value_type, impl_value_type &>>
  value_at(size_type i) const {
    KOKKOS_EXPECTS(i < capacity());
    return m_values[i];
  }

  KOKKOS_FORCEINLINE_FUNCTION
  key_type key_at(size_type i) const {
    KOKKOS_EXPECTS(i < capacity());
    return m_keys[i];
  }
 
  KOKKOS_FORCEINLINE_FUNCTION
  bool valid_at(size_type i) const { return m_available_indexes.test(i); }
 
  template <typename SKey, typename SValue>
  UnorderedMap(
      UnorderedMap<SKey, SValue, Device, Hasher, EqualTo> const &src,
      std::enable_if_t<
          Impl::UnorderedMapCanAssign<declared_key_type, declared_value_type,
                                      SKey, SValue>::value,
          int> = 0)
      : m_bounded_insert(src.m_bounded_insert),
        m_hasher(src.m_hasher),
        m_equal_to(src.m_equal_to),
        m_size(src.m_size),
        m_available_indexes(src.m_available_indexes),
        m_hash_lists(src.m_hash_lists),
        m_next_index(src.m_next_index),
        m_keys(src.m_keys),
        m_values(src.m_values),
        m_scalars(src.m_scalars) {}
 
  template <typename SKey, typename SValue>
  std::enable_if_t<
      Impl::UnorderedMapCanAssign<declared_key_type, declared_value_type, SKey,
                                  SValue>::value,
      declared_map_type &>
  operator=(UnorderedMap<SKey, SValue, Device, Hasher, EqualTo> const &src) {
    m_bounded_insert    = src.m_bounded_insert;
    m_hasher            = src.m_hasher;
    m_equal_to          = src.m_equal_to;
    m_size              = src.m_size;
    m_available_indexes = src.m_available_indexes;
    m_hash_lists        = src.m_hash_lists;
    m_next_index        = src.m_next_index;
    m_keys              = src.m_keys;
    m_values            = src.m_values;
    m_scalars           = src.m_scalars;
    return *this;
  }
 
  template <typename SKey, typename SValue, typename SDevice>
  std::enable_if_t<std::is_same<std::remove_const_t<SKey>, key_type>::value &&
                   std::is_same<std::remove_const_t<SValue>, value_type>::value>
  create_copy_view(
      UnorderedMap<SKey, SValue, SDevice, Hasher, EqualTo> const &src) {
    if (m_hash_lists.data() != src.m_hash_lists.data()) {
      insertable_map_type tmp;
 
      tmp.m_bounded_insert    = src.m_bounded_insert;
      tmp.m_hasher            = src.m_hasher;
      tmp.m_equal_to          = src.m_equal_to;
      tmp.m_size()            = src.m_size();
      tmp.m_available_indexes = bitset_type(src.capacity());
      tmp.m_hash_lists        = size_type_view(
          view_alloc(WithoutInitializing, "UnorderedMap hash list"),
          src.m_hash_lists.extent(0));
      tmp.m_next_index = size_type_view(
          view_alloc(WithoutInitializing, "UnorderedMap next index"),
          src.m_next_index.extent(0));
      tmp.m_keys =
          key_type_view(view_alloc(WithoutInitializing, "UnorderedMap keys"),
                        src.m_keys.extent(0));
      tmp.m_values = value_type_view(
          view_alloc(WithoutInitializing, "UnorderedMap values"),
          src.m_values.extent(0));
      tmp.m_scalars = scalars_view("UnorderedMap scalars");
 
      Kokkos::deep_copy(tmp.m_available_indexes, src.m_available_indexes);
 
      using raw_deep_copy =
          Kokkos::Impl::DeepCopy<typename device_type::memory_space,
                                 typename SDevice::memory_space>;
 
      raw_deep_copy(tmp.m_hash_lists.data(), src.m_hash_lists.data(),
                    sizeof(size_type) * src.m_hash_lists.extent(0));
      raw_deep_copy(tmp.m_next_index.data(), src.m_next_index.data(),
                    sizeof(size_type) * src.m_next_index.extent(0));
      raw_deep_copy(tmp.m_keys.data(), src.m_keys.data(),
                    sizeof(key_type) * src.m_keys.extent(0));
      if (!is_set) {
        raw_deep_copy(tmp.m_values.data(), src.m_values.data(),
                      sizeof(impl_value_type) * src.m_values.extent(0));
      }
      raw_deep_copy(tmp.m_scalars.data(), src.m_scalars.data(),
                    sizeof(int) * num_scalars);
 
      Kokkos::fence(
          "Kokkos::UnorderedMap::create_copy_view: fence after copy to tmp");
 
      *this = tmp;
    }
  }

 private:  // private member functions
  bool modified() const { return get_flag(modified_idx); }
 
  void set_flag(int flag) const {
    using raw_deep_copy =
        Kokkos::Impl::DeepCopy<typename device_type::memory_space,
                               Kokkos::HostSpace>;
    const int true_ = true;
    raw_deep_copy(m_scalars.data() + flag, &true_, sizeof(int));
    Kokkos::fence(
        "Kokkos::UnorderedMap::set_flag: fence after copying flag from "
        "HostSpace");
  }
 
  void reset_flag(int flag) const {
    using raw_deep_copy =
        Kokkos::Impl::DeepCopy<typename device_type::memory_space,
                               Kokkos::HostSpace>;
    const int false_ = false;
    raw_deep_copy(m_scalars.data() + flag, &false_, sizeof(int));
    Kokkos::fence(
        "Kokkos::UnorderedMap::reset_flag: fence after copying flag from "
        "HostSpace");
  }
 
  bool get_flag(int flag) const {
    using raw_deep_copy =
        Kokkos::Impl::DeepCopy<Kokkos::HostSpace,
                               typename device_type::memory_space>;
    int result = false;
    raw_deep_copy(&result, m_scalars.data() + flag, sizeof(int));
    Kokkos::fence(
        "Kokkos::UnorderedMap::get_flag: fence after copy to return value in "
        "HostSpace");
    return result;
  }
 
  static uint32_t calculate_capacity(uint32_t capacity_hint) {
    // increase by 16% and round to nears multiple of 128
    return capacity_hint
               ? ((static_cast<uint32_t>(7ull * capacity_hint / 6u) + 127u) /
                  128u) *
                     128u
               : 128u;
  }
 
 private:  // private members
  bool m_bounded_insert;
  hasher_type m_hasher;
  equal_to_type m_equal_to;
  View<size_type, HostSpace> m_size;
  bitset_type m_available_indexes;
  size_type_view m_hash_lists;
  size_type_view m_next_index;
  key_type_view m_keys;
  value_type_view m_values;
  scalars_view m_scalars;
 
  template <typename KKey, typename VValue, typename DDevice, typename HHash,
            typename EEqualTo>
  friend class UnorderedMap;
 
  template <typename UMap>
  friend struct Impl::UnorderedMapErase;
 
  template <typename UMap>
  friend struct Impl::UnorderedMapHistogram;
 
  template <typename UMap>
  friend struct Impl::UnorderedMapPrint;
};
 
// Specialization of deep_copy for two UnorderedMap objects.
template <typename DKey, typename DT, typename DDevice, typename SKey,
          typename ST, typename SDevice, typename Hasher, typename EqualTo>
inline void deep_copy(
    UnorderedMap<DKey, DT, DDevice, Hasher, EqualTo> &dst,
    const UnorderedMap<SKey, ST, SDevice, Hasher, EqualTo> &src) {
  dst.create_copy_view(src);
}
 
}  // namespace Kokkos
 
#ifdef KOKKOS_IMPL_PUBLIC_INCLUDE_NOTDEFINED_UNORDEREDMAP
#undef KOKKOS_IMPL_PUBLIC_INCLUDE
#undef KOKKOS_IMPL_PUBLIC_INCLUDE_NOTDEFINED_UNORDEREDMAP
#endif
#endif  // KOKKOS_UNORDERED_MAP_HPP