diff options
Diffstat (limited to 'db/snapshot.h')
-rw-r--r-- | db/snapshot.h | 80 |
1 files changed, 55 insertions, 25 deletions
diff --git a/db/snapshot.h b/db/snapshot.h index 6ed413c..e7f115f 100644 --- a/db/snapshot.h +++ b/db/snapshot.h @@ -8,6 +8,7 @@ #include "db/dbformat.h" #include "leveldb/db.h" + namespace leveldb { class SnapshotList; @@ -16,50 +17,79 @@ class SnapshotList; // Each SnapshotImpl corresponds to a particular sequence number. class SnapshotImpl : public Snapshot { public: - SequenceNumber number_; // const after creation + SnapshotImpl(SequenceNumber sequence_number) + : sequence_number_(sequence_number) {} + + SequenceNumber sequence_number() const { return sequence_number_; } private: friend class SnapshotList; - // SnapshotImpl is kept in a doubly-linked circular list + // SnapshotImpl is kept in a doubly-linked circular list. The SnapshotList + // implementation operates on the next/previous fields direcly. SnapshotImpl* prev_; SnapshotImpl* next_; - SnapshotList* list_; // just for sanity checks + const SequenceNumber sequence_number_; + +#if !defined(NDEBUG) + SnapshotList* list_ = nullptr; +#endif // !defined(NDEBUG) }; +inline const SnapshotImpl* ToSnapshotImpl(const Snapshot* snapshot) { + return static_cast<const SnapshotImpl*>(snapshot); +} +inline SnapshotImpl* ToSnapshotImpl(Snapshot* snapshot) { + return static_cast<SnapshotImpl*>(snapshot); +} + class SnapshotList { public: - SnapshotList() { - list_.prev_ = &list_; - list_.next_ = &list_; + SnapshotList() : head_(0) { + head_.prev_ = &head_; + head_.next_ = &head_; } - bool empty() const { return list_.next_ == &list_; } - SnapshotImpl* oldest() const { assert(!empty()); return list_.next_; } - SnapshotImpl* newest() const { assert(!empty()); return list_.prev_; } - - const SnapshotImpl* New(SequenceNumber seq) { - SnapshotImpl* s = new SnapshotImpl; - s->number_ = seq; - s->list_ = this; - s->next_ = &list_; - s->prev_ = list_.prev_; - s->prev_->next_ = s; - s->next_->prev_ = s; - return s; + bool empty() const { return head_.next_ == &head_; } + SnapshotImpl* oldest() const { assert(!empty()); return head_.next_; } + SnapshotImpl* newest() const { assert(!empty()); return head_.prev_; } + + // Creates a SnapshotImpl and appends it to the end of the list. + SnapshotImpl* New(SequenceNumber sequence_number) { + assert(empty() || newest()->sequence_number_ <= sequence_number); + + SnapshotImpl* snapshot = new SnapshotImpl(sequence_number); + +#if !defined(NDEBUG) + snapshot->list_ = this; +#endif // !defined(NDEBUG) + snapshot->next_ = &head_; + snapshot->prev_ = head_.prev_; + snapshot->prev_->next_ = snapshot; + snapshot->next_->prev_ = snapshot; + return snapshot; } - void Delete(const SnapshotImpl* s) { - assert(s->list_ == this); - s->prev_->next_ = s->next_; - s->next_->prev_ = s->prev_; - delete s; + // Removes a SnapshotImpl from this list. + // + // The snapshot must have been created by calling New() on this list. + // + // The snapshot pointer should not be const, because its memory is + // deallocated. However, that would force us to change DB::ReleaseSnapshot(), + // which is in the API, and currently takes a const Snapshot. + void Delete(const SnapshotImpl* snapshot) { +#if !defined(NDEBUG) + assert(snapshot->list_ == this); +#endif // !defined(NDEBUG) + snapshot->prev_->next_ = snapshot->next_; + snapshot->next_->prev_ = snapshot->prev_; + delete snapshot; } private: // Dummy head of doubly-linked list of snapshots - SnapshotImpl list_; + SnapshotImpl head_; }; } // namespace leveldb |