rocksdb/table/iterator_wrapper.h
2016-02-09 15:12:00 -08:00

159 lines
4.5 KiB
C++

// Copyright (c) 2011-present, 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.
//
// Copyright (c) 2011 The LevelDB Authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file. See the AUTHORS file for names of contributors.
#pragma once
#include <set>
#include "table/internal_iterator.h"
namespace rocksdb {
// A internal wrapper class with an interface similar to Iterator that
// caches the valid() and key() results for an underlying iterator.
// This can help avoid virtual function calls and also gives better
// cache locality.
class IteratorWrapper {
public:
IteratorWrapper() : iter_(nullptr), iters_pinned_(false), valid_(false) {}
explicit IteratorWrapper(InternalIterator* _iter)
: iter_(nullptr), iters_pinned_(false) {
Set(_iter);
}
~IteratorWrapper() {}
InternalIterator* iter() const { return iter_; }
// Takes the ownership of "_iter" and will delete it when destroyed.
// Next call to Set() will destroy "_iter" except if PinData() was called.
void Set(InternalIterator* _iter) {
if (iters_pinned_ && iter_) {
// keep old iterator until ReleasePinnedData() is called
pinned_iters_.insert(iter_);
} else {
delete iter_;
}
iter_ = _iter;
if (iter_ == nullptr) {
valid_ = false;
} else {
Update();
if (iters_pinned_) {
// Pin new iterator
Status s = iter_->PinData();
assert(s.ok());
}
}
}
Status PinData() {
Status s;
if (iters_pinned_) {
return s;
}
if (iter_) {
s = iter_->PinData();
}
if (s.ok()) {
iters_pinned_ = true;
}
return s;
}
Status ReleasePinnedData() {
Status s;
if (!iters_pinned_) {
return s;
}
if (iter_) {
s = iter_->ReleasePinnedData();
}
if (s.ok()) {
iters_pinned_ = false;
// No need to call ReleasePinnedData() for pinned_iters_
// since we will delete them
DeletePinnedIterators(false);
}
return s;
}
bool IsKeyPinned() const {
assert(iter_);
return iters_pinned_ && iter_->IsKeyPinned();
}
void DeleteIter(bool is_arena_mode) {
if (iter_ && pinned_iters_.find(iter_) == pinned_iters_.end()) {
DestroyIterator(iter_, is_arena_mode);
}
DeletePinnedIterators(is_arena_mode);
}
// Iterator interface methods
bool Valid() const { return valid_; }
Slice key() const { assert(Valid()); return key_; }
Slice value() const { assert(Valid()); return iter_->value(); }
// Methods below require iter() != nullptr
Status status() const { assert(iter_); return iter_->status(); }
void Next() { assert(iter_); iter_->Next(); Update(); }
void Prev() { assert(iter_); iter_->Prev(); Update(); }
void Seek(const Slice& k) { assert(iter_); iter_->Seek(k); Update(); }
void SeekToFirst() { assert(iter_); iter_->SeekToFirst(); Update(); }
void SeekToLast() { assert(iter_); iter_->SeekToLast(); Update(); }
private:
void Update() {
valid_ = iter_->Valid();
if (valid_) {
key_ = iter_->key();
}
}
void DeletePinnedIterators(bool is_arena_mode) {
for (auto it : pinned_iters_) {
DestroyIterator(it, is_arena_mode);
}
pinned_iters_.clear();
}
inline void DestroyIterator(InternalIterator* it, bool is_arena_mode) {
if (!is_arena_mode) {
delete it;
} else {
it->~InternalIterator();
}
}
InternalIterator* iter_;
// If set to true, current and future iterators wont be deleted.
bool iters_pinned_;
// List of past iterators that are pinned and wont be deleted as long as
// iters_pinned_ is true. When we are pinning iterators this set will contain
// iterators of previous data blocks to keep them from being deleted.
std::set<InternalIterator*> pinned_iters_;
bool valid_;
Slice key_;
};
class Arena;
// Return an empty iterator (yields nothing) allocated from arena.
extern InternalIterator* NewEmptyInternalIterator(Arena* arena);
// Return an empty iterator with the specified status, allocated arena.
extern InternalIterator* NewErrorInternalIterator(const Status& status,
Arena* arena);
} // namespace rocksdb