ceph/src/rocksdb/include/rocksdb/snapshot.h

   1 //  Copyright (c) 2011-present, Facebook, Inc.  All rights reserved.
   2 //  This source code is licensed under both the GPLv2 (found in the
   3 //  COPYING file in the root directory) and Apache 2.0 License
   4 //  (found in the LICENSE.Apache file in the root directory).
   5
   6 #pragma once
   7
   8 #include "rocksdb/types.h"
   9
  10 namespace ROCKSDB_NAMESPACE {
  11
  12 class DB;
  13
  14 // Abstract handle to particular state of a DB.
  15 // A Snapshot is an immutable object and can therefore be safely
  16 // accessed from multiple threads without any external synchronization.
  17 //
  18 // To Create a Snapshot, call DB::GetSnapshot().
  19 // To Destroy a Snapshot, call DB::ReleaseSnapshot(snapshot).
  20 class Snapshot {
  21  public:
  22   // returns Snapshot's sequence number
  23   virtual SequenceNumber GetSequenceNumber() const = 0;
  24
  25  protected:
  26   virtual ~Snapshot();
  27 };
  28
  29 // Simple RAII wrapper class for Snapshot.
  30 // Constructing this object will create a snapshot.  Destructing will
  31 // release the snapshot.
  32 class ManagedSnapshot {
  33  public:
  34   explicit ManagedSnapshot(DB* db);
  35
  36   // Instead of creating a snapshot, take ownership of the input snapshot.
  37   ManagedSnapshot(DB* db, const Snapshot* _snapshot);
  38
  39   ~ManagedSnapshot();
  40
  41   const Snapshot* snapshot();
  42
  43  private:
  44   DB* db_;
  45   const Snapshot* snapshot_;
  46 };
  47
  48 }  // namespace ROCKSDB_NAMESPACE