1 files changed, 149 insertions, 0 deletions
diff --git a/src/rocksdb/db/snapshot_impl.h b/src/rocksdb/db/snapshot_impl.h
new file mode 100644
index 00000000..f2610fd1
--- /dev/null
+++ b/src/rocksdb/db/snapshot_impl.h
@@ -0,0 +1,149 @@
+//  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 {
+
+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;
+
+    if (oldest_write_conflict_snapshot != nullptr) {
+      *oldest_write_conflict_snapshot = kMaxSequenceNumber;
+    }
+
+    if (empty()) {
+      return ret;
+    }
+    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 ret;
+  }
+
+  // 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_;
+    }
+  }
+
+  uint64_t count() const { return count_; }
+
+ private:
+  // Dummy head of doubly-linked list of snapshots
+  SnapshotImpl list_;
+  uint64_t count_;
+};
+
+}  // namespace rocksdb