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diff --git a/src/rocksdb/utilities/persistent_cache/hash_table_evictable.h b/src/rocksdb/utilities/persistent_cache/hash_table_evictable.h
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+// Copyright (c) 2013, 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
+
+#ifndef ROCKSDB_LITE
+
+#include <functional>
+
+#include "util/random.h"
+#include "utilities/persistent_cache/hash_table.h"
+#include "utilities/persistent_cache/lrulist.h"
+
+namespace ROCKSDB_NAMESPACE {
+
+// Evictable Hash Table
+//
+// Hash table index where least accessed (or one of the least accessed) elements
+// can be evicted.
+//
+// Please note EvictableHashTable can only be created for pointer type objects
+template <class T, class Hash, class Equal>
+class EvictableHashTable : private HashTable<T*, Hash, Equal> {
+ public:
+ typedef HashTable<T*, Hash, Equal> hash_table;
+
+ explicit EvictableHashTable(const size_t capacity = 1024 * 1024,
+ const float load_factor = 2.0,
+ const uint32_t nlocks = 256)
+ : HashTable<T*, Hash, Equal>(capacity, load_factor, nlocks),
+ lru_lists_(new LRUList<T>[hash_table::nlocks_]) {
+ assert(lru_lists_);
+ }
+
+ virtual ~EvictableHashTable() { AssertEmptyLRU(); }
+
+ //
+ // Insert given record to hash table (and LRU list)
+ //
+ bool Insert(T* t) {
+ const uint64_t h = Hash()(t);
+ typename hash_table::Bucket& bucket = GetBucket(h);
+ LRUListType& lru = GetLRUList(h);
+ port::RWMutex& lock = GetMutex(h);
+
+ WriteLock _(&lock);
+ if (hash_table::Insert(&bucket, t)) {
+ lru.Push(t);
+ return true;
+ }
+ return false;
+ }
+
+ //
+ // Lookup hash table
+ //
+ // Please note that read lock should be held by the caller. This is because
+ // the caller owns the data, and should hold the read lock as long as he
+ // operates on the data.
+ bool Find(T* t, T** ret) {
+ const uint64_t h = Hash()(t);
+ typename hash_table::Bucket& bucket = GetBucket(h);
+ LRUListType& lru = GetLRUList(h);
+ port::RWMutex& lock = GetMutex(h);
+
+ ReadLock _(&lock);
+ if (hash_table::Find(&bucket, t, ret)) {
+ ++(*ret)->refs_;
+ lru.Touch(*ret);
+ return true;
+ }
+ return false;
+ }
+
+ //
+ // Evict one of the least recently used object
+ //
+ T* Evict(const std::function<void(T*)>& fn = nullptr) {
+ uint32_t random = Random::GetTLSInstance()->Next();
+ const size_t start_idx = random % hash_table::nlocks_;
+ T* t = nullptr;
+
+ // iterate from start_idx .. 0 .. start_idx
+ for (size_t i = 0; !t && i < hash_table::nlocks_; ++i) {
+ const size_t idx = (start_idx + i) % hash_table::nlocks_;
+
+ WriteLock _(&hash_table::locks_[idx]);
+ LRUListType& lru = lru_lists_[idx];
+ if (!lru.IsEmpty() && (t = lru.Pop()) != nullptr) {
+ assert(!t->refs_);
+ // We got an item to evict, erase from the bucket
+ const uint64_t h = Hash()(t);
+ typename hash_table::Bucket& bucket = GetBucket(h);
+ T* tmp = nullptr;
+ bool status = hash_table::Erase(&bucket, t, &tmp);
+ assert(t == tmp);
+ (void)status;
+ assert(status);
+ if (fn) {
+ fn(t);
+ }
+ break;
+ }
+ assert(!t);
+ }
+ return t;
+ }
+
+ void Clear(void (*fn)(T*)) {
+ for (uint32_t i = 0; i < hash_table::nbuckets_; ++i) {
+ const uint32_t lock_idx = i % hash_table::nlocks_;
+ WriteLock _(&hash_table::locks_[lock_idx]);
+ auto& lru_list = lru_lists_[lock_idx];
+ auto& bucket = hash_table::buckets_[i];
+ for (auto* t : bucket.list_) {
+ lru_list.Unlink(t);
+ (*fn)(t);
+ }
+ bucket.list_.clear();
+ }
+ // make sure that all LRU lists are emptied
+ AssertEmptyLRU();
+ }
+
+ void AssertEmptyLRU() {
+#ifndef NDEBUG
+ for (uint32_t i = 0; i < hash_table::nlocks_; ++i) {
+ WriteLock _(&hash_table::locks_[i]);
+ auto& lru_list = lru_lists_[i];
+ assert(lru_list.IsEmpty());
+ }
+#endif
+ }
+
+ //
+ // Fetch the mutex associated with a key
+ // This call is used to hold the lock for a given data for extended period of
+ // time.
+ port::RWMutex* GetMutex(T* t) { return hash_table::GetMutex(t); }
+
+ private:
+ typedef LRUList<T> LRUListType;
+
+ typename hash_table::Bucket& GetBucket(const uint64_t h) {
+ const uint32_t bucket_idx = h % hash_table::nbuckets_;
+ return hash_table::buckets_[bucket_idx];
+ }
+
+ LRUListType& GetLRUList(const uint64_t h) {
+ const uint32_t bucket_idx = h % hash_table::nbuckets_;
+ const uint32_t lock_idx = bucket_idx % hash_table::nlocks_;
+ return lru_lists_[lock_idx];
+ }
+
+ port::RWMutex& GetMutex(const uint64_t h) {
+ const uint32_t bucket_idx = h % hash_table::nbuckets_;
+ const uint32_t lock_idx = bucket_idx % hash_table::nlocks_;
+ return hash_table::locks_[lock_idx];
+ }
+
+ std::unique_ptr<LRUListType[]> lru_lists_;
+};
+
+} // namespace ROCKSDB_NAMESPACE
+
+#endif