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-rw-r--r--src/rocksdb/util/hash_map.h67
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diff --git a/src/rocksdb/util/hash_map.h b/src/rocksdb/util/hash_map.h
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+// Copyright (c) 2011-present, Facebook, Inc. All rights reserved.
+// This source code is licensed under both the GPLv2 (found in the
+// COPYING file in the root directory) and Apache 2.0 License
+// (found in the LICENSE.Apache file in the root directory).
+//
+
+#pragma once
+
+#include <algorithm>
+#include <array>
+#include <utility>
+
+#include "util/autovector.h"
+
+namespace ROCKSDB_NAMESPACE {
+
+// This is similar to std::unordered_map, except that it tries to avoid
+// allocating or deallocating memory as much as possible. With
+// std::unordered_map, an allocation/deallocation is made for every insertion
+// or deletion because of the requirement that iterators remain valid even
+// with insertions or deletions. This means that the hash chains will be
+// implemented as linked lists.
+//
+// This implementation uses autovector as hash chains insteads.
+//
+template <typename K, typename V, size_t size = 128>
+class HashMap {
+ std::array<autovector<std::pair<K, V>, 1>, size> table_;
+
+ public:
+ bool Contains(K key) {
+ auto& bucket = table_[key % size];
+ auto it = std::find_if(
+ bucket.begin(), bucket.end(),
+ [key](const std::pair<K, V>& p) { return p.first == key; });
+ return it != bucket.end();
+ }
+
+ void Insert(K key, V value) {
+ auto& bucket = table_[key % size];
+ bucket.push_back({key, value});
+ }
+
+ void Delete(K key) {
+ auto& bucket = table_[key % size];
+ auto it = std::find_if(
+ bucket.begin(), bucket.end(),
+ [key](const std::pair<K, V>& p) { return p.first == key; });
+ if (it != bucket.end()) {
+ auto last = bucket.end() - 1;
+ if (it != last) {
+ *it = *last;
+ }
+ bucket.pop_back();
+ }
+ }
+
+ V& Get(K key) {
+ auto& bucket = table_[key % size];
+ auto it = std::find_if(
+ bucket.begin(), bucket.end(),
+ [key](const std::pair<K, V>& p) { return p.first == key; });
+ return it->second;
+ }
+};
+
+} // namespace ROCKSDB_NAMESPACE