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rocksdb/util/hash_skiplist_rep.cc

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// Copyright (c) 2013, Facebook, Inc. All rights reserved.
// This source code is licensed under the BSD-style license found in the
// LICENSE file in the root directory of this source tree. An additional grant
// of patent rights can be found in the PATENTS file in the same directory.
//
#include "util/hash_skiplist_rep.h"
#include "rocksdb/memtablerep.h"
#include "rocksdb/arena.h"
#include "rocksdb/slice.h"
#include "rocksdb/slice_transform.h"
#include "port/port.h"
#include "port/atomic_pointer.h"
#include "util/murmurhash.h"
#include "db/skiplist.h"
namespace rocksdb {
namespace {
class HashSkipListRep : public MemTableRep {
public:
HashSkipListRep(MemTableRep::KeyComparator& compare, Arena* arena,
const SliceTransform* transform, size_t bucket_size);
virtual void Insert(const char* key) override;
virtual bool Contains(const char* key) const override;
virtual size_t ApproximateMemoryUsage() override;
virtual ~HashSkipListRep();
virtual std::shared_ptr<MemTableRep::Iterator> GetIterator() override;
virtual std::shared_ptr<MemTableRep::Iterator> GetIterator(
const Slice& slice) override;
virtual std::shared_ptr<MemTableRep::Iterator> GetPrefixIterator(
const Slice& prefix) override;
virtual std::shared_ptr<MemTableRep::Iterator> GetDynamicPrefixIterator()
override;
private:
friend class DynamicIterator;
typedef SkipList<const char*, MemTableRep::KeyComparator&> Bucket;
size_t bucket_size_;
// Maps slices (which are transformed user keys) to buckets of keys sharing
// the same transform.
port::AtomicPointer* buckets_;
// The user-supplied transform whose domain is the user keys.
const SliceTransform* transform_;
MemTableRep::KeyComparator& compare_;
// immutable after construction
Arena* const arena_;
inline size_t GetHash(const Slice& slice) const {
return MurmurHash(slice.data(), slice.size(), 0) % bucket_size_;
}
inline Bucket* GetBucket(size_t i) const {
return static_cast<Bucket*>(buckets_[i].Acquire_Load());
}
inline Bucket* GetBucket(const Slice& slice) const {
return GetBucket(GetHash(slice));
}
// Get a bucket from buckets_. If the bucket hasn't been initialized yet,
// initialize it before returning.
Bucket* GetInitializedBucket(const Slice& transformed);
class Iterator : public MemTableRep::Iterator {
public:
explicit Iterator(Bucket* list, bool own_list = true)
: list_(list),
iter_(list),
own_list_(own_list) {}
virtual ~Iterator() {
// if we own the list, we should also delete it
if (own_list_) {
assert(list_ != nullptr);
delete list_;
}
}
// Returns true iff the iterator is positioned at a valid node.
virtual bool Valid() const {
return list_ != nullptr && iter_.Valid();
}
// Returns the key at the current position.
// REQUIRES: Valid()
virtual const char* key() const {
assert(Valid());
return iter_.key();
}
// Advances to the next position.
// REQUIRES: Valid()
virtual void Next() {
assert(Valid());
iter_.Next();
}
// Advances to the previous position.
// REQUIRES: Valid()
virtual void Prev() {
assert(Valid());
iter_.Prev();
}
// Advance to the first entry with a key >= target
virtual void Seek(const char* target) {
if (list_ != nullptr) {
iter_.Seek(target);
}
}
// Position at the first entry in collection.
// Final state of iterator is Valid() iff collection is not empty.
virtual void SeekToFirst() {
if (list_ != nullptr) {
iter_.SeekToFirst();
}
}
// Position at the last entry in collection.
// Final state of iterator is Valid() iff collection is not empty.
virtual void SeekToLast() {
if (list_ != nullptr) {
iter_.SeekToLast();
}
}
protected:
void Reset(Bucket* list) {
if (own_list_) {
assert(list_ != nullptr);
delete list_;
}
list_ = list;
iter_.SetList(list);
own_list_ = false;
}
private:
// if list_ is nullptr, we should NEVER call any methods on iter_
// if list_ is nullptr, this Iterator is not Valid()
Bucket* list_;
Bucket::Iterator iter_;
// here we track if we own list_. If we own it, we are also
// responsible for it's cleaning. This is a poor man's shared_ptr
bool own_list_;
};
class DynamicIterator : public HashSkipListRep::Iterator {
public:
explicit DynamicIterator(const HashSkipListRep& memtable_rep)
: HashSkipListRep::Iterator(nullptr, false),
memtable_rep_(memtable_rep) {}
// Advance to the first entry with a key >= target
virtual void Seek(const char* target) {
auto transformed = memtable_rep_.transform_->Transform(
memtable_rep_.UserKey(target));
Reset(memtable_rep_.GetBucket(transformed));
HashSkipListRep::Iterator::Seek(target);
}
// Position at the first entry in collection.
// Final state of iterator is Valid() iff collection is not empty.
virtual void SeekToFirst() {
// Prefix iterator does not support total order.
// We simply set the iterator to invalid state
Reset(nullptr);
}
// Position at the last entry in collection.
// Final state of iterator is Valid() iff collection is not empty.
virtual void SeekToLast() {
// Prefix iterator does not support total order.
// We simply set the iterator to invalid state
Reset(nullptr);
}
private:
// the underlying memtable
const HashSkipListRep& memtable_rep_;
};
class EmptyIterator : public MemTableRep::Iterator {
// This is used when there wasn't a bucket. It is cheaper than
// instantiating an empty bucket over which to iterate.
public:
EmptyIterator() { }
virtual bool Valid() const {
return false;
}
virtual const char* key() const {
assert(false);
return nullptr;
}
virtual void Next() { }
virtual void Prev() { }
virtual void Seek(const char* target) { }
virtual void SeekToFirst() { }
virtual void SeekToLast() { }
private:
};
std::shared_ptr<EmptyIterator> empty_iterator_;
};
HashSkipListRep::HashSkipListRep(MemTableRep::KeyComparator& compare,
Arena* arena, const SliceTransform* transform, size_t bucket_size)
: bucket_size_(bucket_size),
transform_(transform),
compare_(compare),
arena_(arena),
empty_iterator_(std::make_shared<EmptyIterator>()) {
buckets_ = new port::AtomicPointer[bucket_size];
for (size_t i = 0; i < bucket_size_; ++i) {
buckets_[i].NoBarrier_Store(nullptr);
}
}
HashSkipListRep::~HashSkipListRep() {
delete[] buckets_;
}
HashSkipListRep::Bucket* HashSkipListRep::GetInitializedBucket(
const Slice& transformed) {
size_t hash = GetHash(transformed);
auto bucket = GetBucket(hash);
if (bucket == nullptr) {
auto addr = arena_->AllocateAligned(sizeof(Bucket));
bucket = new (addr) Bucket(compare_, arena_);
buckets_[hash].Release_Store(static_cast<void*>(bucket));
}
return bucket;
}
void HashSkipListRep::Insert(const char* key) {
assert(!Contains(key));
auto transformed = transform_->Transform(UserKey(key));
auto bucket = GetInitializedBucket(transformed);
bucket->Insert(key);
}
bool HashSkipListRep::Contains(const char* key) const {
auto transformed = transform_->Transform(UserKey(key));
auto bucket = GetBucket(transformed);
if (bucket == nullptr) {
return false;
}
return bucket->Contains(key);
}
size_t HashSkipListRep::ApproximateMemoryUsage() {
return sizeof(buckets_);
}
std::shared_ptr<MemTableRep::Iterator> HashSkipListRep::GetIterator() {
auto list = new Bucket(compare_, arena_);
for (size_t i = 0; i < bucket_size_; ++i) {
auto bucket = GetBucket(i);
if (bucket != nullptr) {
Bucket::Iterator itr(bucket);
for (itr.SeekToFirst(); itr.Valid(); itr.Next()) {
list->Insert(itr.key());
}
}
}
return std::make_shared<Iterator>(list);
}
std::shared_ptr<MemTableRep::Iterator> HashSkipListRep::GetPrefixIterator(
const Slice& prefix) {
auto bucket = GetBucket(prefix);
if (bucket == nullptr) {
return empty_iterator_;
}
return std::make_shared<Iterator>(bucket, false);
}
std::shared_ptr<MemTableRep::Iterator> HashSkipListRep::GetIterator(
const Slice& slice) {
return GetPrefixIterator(transform_->Transform(slice));
}
std::shared_ptr<MemTableRep::Iterator>
HashSkipListRep::GetDynamicPrefixIterator() {
return std::make_shared<DynamicIterator>(*this);
}
} // anon namespace
std::shared_ptr<MemTableRep>
HashSkipListRepFactory::CreateMemTableRep(MemTableRep::KeyComparator &compare,
Arena *arena) {
return std::make_shared<HashSkipListRep>(compare, arena, transform_,
bucket_count_);
}
MemTableRepFactory* NewHashSkipListRepFactory(
const SliceTransform* transform, size_t bucket_count) {
return new HashSkipListRepFactory(transform, bucket_count);
}
} // namespace rocksdb