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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).
//
// 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 <vector>
#include "rocksdb/db.h"
namespace ROCKSDB_NAMESPACE {
class SnapshotList;
// Snapshots are kept in a doubly-linked list in the DB.
// Each SnapshotImpl corresponds to a particular sequence number.
class SnapshotImpl : public Snapshot {
public:
SequenceNumber number_; // const after creation
// It indicates the smallest uncommitted data at the time the snapshot was
// taken. This is currently used by WritePrepared transactions to limit the
// scope of queries to IsInSnpashot.
SequenceNumber min_uncommitted_ = kMinUnCommittedSeq;
virtual SequenceNumber GetSequenceNumber() const override { return number_; }
private:
friend class SnapshotList;
// SnapshotImpl is kept in a doubly-linked circular list
SnapshotImpl* prev_;
SnapshotImpl* next_;
SnapshotList* list_; // just for sanity checks
int64_t unix_time_;
// Will this snapshot be used by a Transaction to do write-conflict checking?
bool is_write_conflict_boundary_;
};
class SnapshotList {
public:
SnapshotList() {
list_.prev_ = &list_;
list_.next_ = &list_;
list_.number_ = 0xFFFFFFFFL; // placeholder marker, for debugging
// Set all the variables to make UBSAN happy.
list_.list_ = nullptr;
list_.unix_time_ = 0;
list_.is_write_conflict_boundary_ = false;
count_ = 0;
}
// No copy-construct.
SnapshotList(const SnapshotList&) = delete;
bool empty() const { return list_.next_ == &list_; }
SnapshotImpl* oldest() const { assert(!empty()); return list_.next_; }
SnapshotImpl* newest() const { assert(!empty()); return list_.prev_; }
SnapshotImpl* New(SnapshotImpl* s, SequenceNumber seq, uint64_t unix_time,
bool is_write_conflict_boundary) {
s->number_ = seq;
s->unix_time_ = unix_time;
s->is_write_conflict_boundary_ = is_write_conflict_boundary;
s->list_ = this;
s->next_ = &list_;
s->prev_ = list_.prev_;
s->prev_->next_ = s;
s->next_->prev_ = s;
count_++;
return s;
}
// Do not responsible to free the object.
void Delete(const SnapshotImpl* s) {
assert(s->list_ == this);
s->prev_->next_ = s->next_;
s->next_->prev_ = s->prev_;
count_--;
}
// retrieve all snapshot numbers up until max_seq. They are sorted in
// ascending order (with no duplicates).
std::vector<SequenceNumber> GetAll(
SequenceNumber* oldest_write_conflict_snapshot = nullptr,
const SequenceNumber& max_seq = kMaxSequenceNumber) const {
std::vector<SequenceNumber> ret;
GetAll(&ret, oldest_write_conflict_snapshot, max_seq);
return ret;
}
void GetAll(std::vector<SequenceNumber>* snap_vector,
SequenceNumber* oldest_write_conflict_snapshot = nullptr,
const SequenceNumber& max_seq = kMaxSequenceNumber) const {
std::vector<SequenceNumber>& ret = *snap_vector;
// So far we have no use case that would pass a non-empty vector
assert(ret.size() == 0);
if (oldest_write_conflict_snapshot != nullptr) {
*oldest_write_conflict_snapshot = kMaxSequenceNumber;
}
if (empty()) {
return;
}
const SnapshotImpl* s = &list_;
while (s->next_ != &list_) {
if (s->next_->number_ > max_seq) {
break;
}
// Avoid duplicates
if (ret.empty() || ret.back() != s->next_->number_) {
ret.push_back(s->next_->number_);
}
if (oldest_write_conflict_snapshot != nullptr &&
*oldest_write_conflict_snapshot == kMaxSequenceNumber &&
s->next_->is_write_conflict_boundary_) {
// If this is the first write-conflict boundary snapshot in the list,
// it is the oldest
*oldest_write_conflict_snapshot = s->next_->number_;
}
s = s->next_;
}
return;
}
// get the sequence number of the most recent snapshot
SequenceNumber GetNewest() {
if (empty()) {
return 0;
}
return newest()->number_;
}
int64_t GetOldestSnapshotTime() const {
if (empty()) {
return 0;
} else {
return oldest()->unix_time_;
}
}
int64_t GetOldestSnapshotSequence() const {
if (empty()) {
return 0;
} else {
return oldest()->GetSequenceNumber();
}
}
uint64_t count() const { return count_; }
private:
// Dummy head of doubly-linked list of snapshots
SnapshotImpl list_;
uint64_t count_;
};
} // namespace ROCKSDB_NAMESPACE
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