ceph/src/rocksdb/db/managed_iterator.h

   1 //  Copyright (c) 2011-present, Facebook, Inc.  All rights reserved.
   2 //  This source code is licensed under the BSD-style license found in the
   3 //  LICENSE file in the root directory of this source tree. An additional grant
   4 //  of patent rights can be found in the PATENTS file in the same directory.
   5 #pragma once
   6
   7 #ifndef ROCKSDB_LITE
   8
   9 #include <mutex>
  10 #include <queue>
  11 #include <string>
  12 #include <vector>
  13
  14 #include "db/column_family.h"
  15 #include "rocksdb/db.h"
  16 #include "rocksdb/iterator.h"
  17 #include "rocksdb/options.h"
  18 #include "util/arena.h"
  19
  20 namespace rocksdb {
  21
  22 class DBImpl;
  23 struct SuperVersion;
  24 class ColumnFamilyData;
  25
  26 /**
  27  * ManagedIterator is a special type of iterator that supports freeing the
  28  * underlying iterator and still being able to access the current key/value
  29  * pair.  This is done by copying the key/value pair so that clients can
  30  * continue to access the data without getting a SIGSEGV.
  31  * The underlying iterator can be freed manually through the  call to
  32  * ReleaseIter or automatically (as needed on space pressure or age.)
  33  * The iterator is recreated using the saved original arguments.
  34  */
  35 class ManagedIterator : public Iterator {
  36  public:
  37   ManagedIterator(DBImpl* db, const ReadOptions& read_options,
  38                   ColumnFamilyData* cfd);
  39   virtual ~ManagedIterator();
  40
  41   virtual void SeekToLast() override;
  42   virtual void Prev() override;
  43   virtual bool Valid() const override;
  44   void SeekToFirst() override;
  45   virtual void Seek(const Slice& target) override;
  46   virtual void SeekForPrev(const Slice& target) override;
  47   virtual void Next() override;
  48   virtual Slice key() const override;
  49   virtual Slice value() const override;
  50   virtual Status status() const override;
  51   void ReleaseIter(bool only_old);
  52   void SetDropOld(bool only_old) {
  53     only_drop_old_ = read_options_.tailing || only_old;
  54   }
  55
  56  private:
  57   void RebuildIterator();
  58   void UpdateCurrent();
  59   void SeekInternal(const Slice& user_key, bool seek_to_first);
  60   bool NeedToRebuild();
  61   void Lock();
  62   bool TryLock();
  63   void UnLock();
  64   DBImpl* const db_;
  65   ReadOptions read_options_;
  66   ColumnFamilyData* const cfd_;
  67   ColumnFamilyHandleInternal cfh_;
  68
  69   uint64_t svnum_;
  70   std::unique_ptr<Iterator> mutable_iter_;
  71   // internal iterator status
  72   Status status_;
  73   bool valid_;
  74
  75   IterKey cached_key_;
  76   IterKey cached_value_;
  77
  78   bool only_drop_old_ = true;
  79   bool snapshot_created_;
  80   bool release_supported_;
  81   std::mutex in_use_;  // is managed iterator in use
  82 };
  83
  84 }  // namespace rocksdb
  85 #endif  // !ROCKSDB_LITE