3c327ac2d0
Summary: Closes https://github.com/facebook/rocksdb/pull/2589 Differential Revision: D5431502 Pulled By: siying fbshipit-source-id: 8ebf8c87883daa9daa54b2303d11ce01ab1f6f75
239 lines
6.4 KiB
C++
239 lines
6.4 KiB
C++
// Copyright (c) 2013, Facebook, Inc. All rights reserved.
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// This source code is licensed under both the GPLv2 (found in the
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// COPYING file in the root directory) and Apache 2.0 License
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// (found in the LICENSE.Apache file in the root directory).
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//
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#pragma once
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#ifndef ROCKSDB_LITE
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#include <assert.h>
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#include <list>
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#include <vector>
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#ifdef OS_LINUX
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#include <sys/mman.h>
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#endif
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#include "include/rocksdb/env.h"
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#include "util/mutexlock.h"
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namespace rocksdb {
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// HashTable<T, Hash, Equal>
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//
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// Traditional implementation of hash table with synchronization built on top
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// don't perform very well in multi-core scenarios. This is an implementation
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// designed for multi-core scenarios with high lock contention.
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//
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// |<-------- alpha ------------->|
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// Buckets Collision list
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// ---- +----+ +---+---+--- ...... ---+---+---+
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// / | |--->| | | | | |
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// / +----+ +---+---+--- ...... ---+---+---+
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// / | |
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// Locks/ +----+
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// +--+/ . .
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// | | . .
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// +--+ . .
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// | | . .
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// +--+ . .
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// | | . .
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// +--+ . .
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// \ +----+
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// \ | |
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// \ +----+
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// \ | |
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// \---- +----+
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//
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// The lock contention is spread over an array of locks. This helps improve
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// concurrent access. The spine is designed for a certain capacity and load
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// factor. When the capacity planning is done correctly we can expect
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// O(load_factor = 1) insert, access and remove time.
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//
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// Micro benchmark on debug build gives about .5 Million/sec rate of insert,
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// erase and lookup in parallel (total of about 1.5 Million ops/sec). If the
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// blocks were of 4K, the hash table can support a virtual throughput of
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// 6 GB/s.
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//
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// T Object type (contains both key and value)
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// Hash Function that returns an hash from type T
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// Equal Returns if two objects are equal
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// (We need explicit equal for pointer type)
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//
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template <class T, class Hash, class Equal>
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class HashTable {
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public:
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explicit HashTable(const size_t capacity = 1024 * 1024,
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const float load_factor = 2.0, const uint32_t nlocks = 256)
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: nbuckets_(
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static_cast<uint32_t>(load_factor ? capacity / load_factor : 0)),
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nlocks_(nlocks) {
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// pre-conditions
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assert(capacity);
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assert(load_factor);
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assert(nbuckets_);
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assert(nlocks_);
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buckets_.reset(new Bucket[nbuckets_]);
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#ifdef OS_LINUX
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mlock(buckets_.get(), nbuckets_ * sizeof(Bucket));
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#endif
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// initialize locks
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locks_.reset(new port::RWMutex[nlocks_]);
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#ifdef OS_LINUX
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mlock(locks_.get(), nlocks_ * sizeof(port::RWMutex));
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#endif
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// post-conditions
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assert(buckets_);
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assert(locks_);
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}
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virtual ~HashTable() { AssertEmptyBuckets(); }
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//
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// Insert given record to hash table
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//
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bool Insert(const T& t) {
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const uint64_t h = Hash()(t);
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const uint32_t bucket_idx = h % nbuckets_;
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const uint32_t lock_idx = bucket_idx % nlocks_;
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WriteLock _(&locks_[lock_idx]);
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auto& bucket = buckets_[bucket_idx];
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return Insert(&bucket, t);
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}
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// Lookup hash table
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//
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// Please note that read lock should be held by the caller. This is because
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// the caller owns the data, and should hold the read lock as long as he
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// operates on the data.
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bool Find(const T& t, T* ret, port::RWMutex** ret_lock) {
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const uint64_t h = Hash()(t);
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const uint32_t bucket_idx = h % nbuckets_;
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const uint32_t lock_idx = bucket_idx % nlocks_;
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port::RWMutex& lock = locks_[lock_idx];
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lock.ReadLock();
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auto& bucket = buckets_[bucket_idx];
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if (Find(&bucket, t, ret)) {
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*ret_lock = &lock;
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return true;
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}
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lock.ReadUnlock();
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return false;
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}
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//
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// Erase a given key from the hash table
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//
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bool Erase(const T& t, T* ret) {
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const uint64_t h = Hash()(t);
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const uint32_t bucket_idx = h % nbuckets_;
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const uint32_t lock_idx = bucket_idx % nlocks_;
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WriteLock _(&locks_[lock_idx]);
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auto& bucket = buckets_[bucket_idx];
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return Erase(&bucket, t, ret);
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}
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// Fetch the mutex associated with a key
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// This call is used to hold the lock for a given data for extended period of
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// time.
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port::RWMutex* GetMutex(const T& t) {
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const uint64_t h = Hash()(t);
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const uint32_t bucket_idx = h % nbuckets_;
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const uint32_t lock_idx = bucket_idx % nlocks_;
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return &locks_[lock_idx];
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}
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void Clear(void (*fn)(T)) {
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for (uint32_t i = 0; i < nbuckets_; ++i) {
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const uint32_t lock_idx = i % nlocks_;
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WriteLock _(&locks_[lock_idx]);
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for (auto& t : buckets_[i].list_) {
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(*fn)(t);
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}
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buckets_[i].list_.clear();
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}
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}
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protected:
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// Models bucket of keys that hash to the same bucket number
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struct Bucket {
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std::list<T> list_;
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};
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// Substitute for std::find with custom comparator operator
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typename std::list<T>::iterator Find(std::list<T>* list, const T& t) {
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for (auto it = list->begin(); it != list->end(); ++it) {
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if (Equal()(*it, t)) {
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return it;
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}
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}
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return list->end();
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}
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bool Insert(Bucket* bucket, const T& t) {
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// Check if the key already exists
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auto it = Find(&bucket->list_, t);
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if (it != bucket->list_.end()) {
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return false;
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}
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// insert to bucket
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bucket->list_.push_back(t);
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return true;
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}
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bool Find(Bucket* bucket, const T& t, T* ret) {
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auto it = Find(&bucket->list_, t);
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if (it != bucket->list_.end()) {
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if (ret) {
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*ret = *it;
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}
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return true;
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}
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return false;
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}
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bool Erase(Bucket* bucket, const T& t, T* ret) {
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auto it = Find(&bucket->list_, t);
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if (it != bucket->list_.end()) {
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if (ret) {
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*ret = *it;
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}
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bucket->list_.erase(it);
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return true;
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}
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return false;
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}
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// assert that all buckets are empty
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void AssertEmptyBuckets() {
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#ifndef NDEBUG
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for (size_t i = 0; i < nbuckets_; ++i) {
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WriteLock _(&locks_[i % nlocks_]);
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assert(buckets_[i].list_.empty());
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}
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#endif
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}
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const uint32_t nbuckets_; // No. of buckets in the spine
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std::unique_ptr<Bucket[]> buckets_; // Spine of the hash buckets
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const uint32_t nlocks_; // No. of locks
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std::unique_ptr<port::RWMutex[]> locks_; // Granular locks
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};
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} // namespace rocksdb
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#endif
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