From 48cd2c3f351ff188bc85684b84a91b6e6d17d896 Mon Sep 17 00:00:00 2001 From: Abseil Team Date: Thu, 27 Sep 2018 12:24:54 -0700 Subject: Export of internal Abseil changes. -- 4eacae3ff1b14b1d309e8092185bc10e8a6203cf by Derek Mauro : Release SwissTable - a fast, efficient, cache-friendly hash table. https://www.youtube.com/watch?v=ncHmEUmJZf4 PiperOrigin-RevId: 214816527 -- df8c3dfab3cfb2f4365909a84d0683b193cfbb11 by Derek Mauro : Internal change PiperOrigin-RevId: 214785288 -- 1eabd5266bbcebc33eecc91e5309b751856a75c8 by Abseil Team : Internal change PiperOrigin-RevId: 214722931 -- 2ebbfac950f83146b46253038e7dd7dcde9f2951 by Derek Mauro : Internal change PiperOrigin-RevId: 214701684 GitOrigin-RevId: 4eacae3ff1b14b1d309e8092185bc10e8a6203cf Change-Id: I9ba64e395b22ad7863213d157b8019b082adc19d --- absl/container/internal/hashtable_debug.h | 108 ++++++++++++++++++++++++++++++ 1 file changed, 108 insertions(+) create mode 100644 absl/container/internal/hashtable_debug.h (limited to 'absl/container/internal/hashtable_debug.h') diff --git a/absl/container/internal/hashtable_debug.h b/absl/container/internal/hashtable_debug.h new file mode 100644 index 00000000..c3bd65c9 --- /dev/null +++ b/absl/container/internal/hashtable_debug.h @@ -0,0 +1,108 @@ +// 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 +// +// http://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. +// +// This library provides APIs to debug the probing behavior of hash tables. +// +// In general, the probing behavior is a black box for users and only the +// side effects can be measured in the form of performance differences. +// These APIs give a glimpse on the actual behavior of the probing algorithms in +// these hashtables given a specified hash function and a set of elements. +// +// The probe count distribution can be used to assess the quality of the hash +// function for that particular hash table. Note that a hash function that +// performs well in one hash table implementation does not necessarily performs +// well in a different one. +// +// This library supports std::unordered_{set,map}, dense_hash_{set,map} and +// absl::{flat,node,string}_hash_{set,map}. + +#ifndef ABSL_CONTAINER_INTERNAL_HASHTABLE_DEBUG_H_ +#define ABSL_CONTAINER_INTERNAL_HASHTABLE_DEBUG_H_ + +#include +#include +#include +#include + +#include "absl/container/internal/hashtable_debug_hooks.h" + +namespace absl { +namespace container_internal { + +// Returns the number of probes required to lookup `key`. Returns 0 for a +// search with no collisions. Higher values mean more hash collisions occurred; +// however, the exact meaning of this number varies according to the container +// type. +template +size_t GetHashtableDebugNumProbes( + const C& c, const typename C::key_type& key) { + return absl::container_internal::hashtable_debug_internal:: + HashtableDebugAccess::GetNumProbes(c, key); +} + +// Gets a histogram of the number of probes for each elements in the container. +// The sum of all the values in the vector is equal to container.size(). +template +std::vector GetHashtableDebugNumProbesHistogram(const C& container) { + std::vector v; + for (auto it = container.begin(); it != container.end(); ++it) { + size_t num_probes = GetHashtableDebugNumProbes( + container, + absl::container_internal::hashtable_debug_internal::GetKey(*it, 0)); + v.resize(std::max(v.size(), num_probes + 1)); + v[num_probes]++; + } + return v; +} + +struct HashtableDebugProbeSummary { + size_t total_elements; + size_t total_num_probes; + double mean; +}; + +// Gets a summary of the probe count distribution for the elements in the +// container. +template +HashtableDebugProbeSummary GetHashtableDebugProbeSummary(const C& container) { + auto probes = GetHashtableDebugNumProbesHistogram(container); + HashtableDebugProbeSummary summary = {}; + for (size_t i = 0; i < probes.size(); ++i) { + summary.total_elements += probes[i]; + summary.total_num_probes += probes[i] * i; + } + summary.mean = 1.0 * summary.total_num_probes / summary.total_elements; + return summary; +} + +// Returns the number of bytes requested from the allocator by the container +// and not freed. +template +size_t AllocatedByteSize(const C& c) { + return absl::container_internal::hashtable_debug_internal:: + HashtableDebugAccess::AllocatedByteSize(c); +} + +// Returns a tight lower bound for AllocatedByteSize(c) where `c` is of type `C` +// and `c.size()` is equal to `num_elements`. +template +size_t LowerBoundAllocatedByteSize(size_t num_elements) { + return absl::container_internal::hashtable_debug_internal:: + HashtableDebugAccess::LowerBoundAllocatedByteSize(num_elements); +} + +} // namespace container_internal +} // namespace absl + +#endif // ABSL_CONTAINER_INTERNAL_HASHTABLE_DEBUG_H_ -- cgit v1.2.3