hashtable_debug_hooks.h

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// Copyright 2018 The Abseil Authors.
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
//      https://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.
//
// Provides the internal API for hashtable_debug.h.

#ifndef ABSL_CONTAINER_INTERNAL_HASHTABLE_DEBUG_HOOKS_H_
#define ABSL_CONTAINER_INTERNAL_HASHTABLE_DEBUG_HOOKS_H_

#include <cstddef>

#include <algorithm>
#include <type_traits>
#include <vector>

namespace absl {
namespace container_internal {
namespace hashtable_debug_internal {

// If it is a map, call get<0>().
using std::get;
template <typename T, typename = typename T::mapped_type>
auto GetKey(const typename T::value_type& pair, int) -> decltype(get<0>(pair)) {
  return get<0>(pair);
}

// If it is not a map, return the value directly.
template <typename T>
const typename T::key_type& GetKey(const typename T::key_type& key, char) {
  return key;
}

// Containers should specialize this to provide debug information for that
// container.
template <class Container, typename Enabler = void>
struct HashtableDebugAccess {
  // Returns the number of probes required to find `key` in `c`.  The "number of
  // probes" is a concept that can vary by container.  Implementations should
  // return 0 when `key` was found in the minimum number of operations and
  // should increment the result for each non-trivial operation required to find
  // `key`.
  //
  // The default implementation uses the bucket api from the standard and thus
  // works for `std::unordered_*` containers.
  static size_t GetNumProbes(const Container& c,
                             const typename Container::key_type& key) {
    if (!c.bucket_count()) return {};
    size_t num_probes = 0;
    size_t bucket = c.bucket(key);
    for (auto it = c.begin(bucket), e = c.end(bucket);; ++it, ++num_probes) {
      if (it == e) return num_probes;
      if (c.key_eq()(key, GetKey<Container>(*it, 0))) return num_probes;
    }
  }

  // Returns the number of bytes requested from the allocator by the container
  // and not freed.
  //
  // static size_t AllocatedByteSize(const Container& c);

  // Returns a tight lower bound for AllocatedByteSize(c) where `c` is of type
  // `Container` and `c.size()` is equal to `num_elements`.
  //
  // static size_t LowerBoundAllocatedByteSize(size_t num_elements);
};

}  // namespace hashtable_debug_internal
}  // namespace container_internal
}  // namespace absl

#endif  // ABSL_CONTAINER_INTERNAL_HASHTABLE_DEBUG_HOOKS_H_