diff options
Diffstat (limited to 'vendor/github.com/syndtr/goleveldb/leveldb/db_snapshot.go')
-rw-r--r-- | vendor/github.com/syndtr/goleveldb/leveldb/db_snapshot.go | 183 |
1 files changed, 183 insertions, 0 deletions
diff --git a/vendor/github.com/syndtr/goleveldb/leveldb/db_snapshot.go b/vendor/github.com/syndtr/goleveldb/leveldb/db_snapshot.go new file mode 100644 index 0000000..2c69d2e --- /dev/null +++ b/vendor/github.com/syndtr/goleveldb/leveldb/db_snapshot.go @@ -0,0 +1,183 @@ +// Copyright (c) 2012, Suryandaru Triandana <syndtr@gmail.com> +// All rights reserved. +// +// Use of this source code is governed by a BSD-style license that can be +// found in the LICENSE file. + +package leveldb + +import ( + "container/list" + "fmt" + "runtime" + "sync" + "sync/atomic" + + "github.com/syndtr/goleveldb/leveldb/iterator" + "github.com/syndtr/goleveldb/leveldb/opt" + "github.com/syndtr/goleveldb/leveldb/util" +) + +type snapshotElement struct { + seq uint64 + ref int + e *list.Element +} + +// Acquires a snapshot, based on latest sequence. +func (db *DB) acquireSnapshot() *snapshotElement { + db.snapsMu.Lock() + defer db.snapsMu.Unlock() + + seq := db.getSeq() + + if e := db.snapsList.Back(); e != nil { + se := e.Value.(*snapshotElement) + if se.seq == seq { + se.ref++ + return se + } else if seq < se.seq { + panic("leveldb: sequence number is not increasing") + } + } + se := &snapshotElement{seq: seq, ref: 1} + se.e = db.snapsList.PushBack(se) + return se +} + +// Releases given snapshot element. +func (db *DB) releaseSnapshot(se *snapshotElement) { + db.snapsMu.Lock() + defer db.snapsMu.Unlock() + + se.ref-- + if se.ref == 0 { + db.snapsList.Remove(se.e) + se.e = nil + } else if se.ref < 0 { + panic("leveldb: Snapshot: negative element reference") + } +} + +// Gets minimum sequence that not being snapshotted. +func (db *DB) minSeq() uint64 { + db.snapsMu.Lock() + defer db.snapsMu.Unlock() + + if e := db.snapsList.Front(); e != nil { + return e.Value.(*snapshotElement).seq + } + + return db.getSeq() +} + +// Snapshot is a DB snapshot. +type Snapshot struct { + db *DB + elem *snapshotElement + mu sync.RWMutex + released bool +} + +// Creates new snapshot object. +func (db *DB) newSnapshot() *Snapshot { + snap := &Snapshot{ + db: db, + elem: db.acquireSnapshot(), + } + atomic.AddInt32(&db.aliveSnaps, 1) + runtime.SetFinalizer(snap, (*Snapshot).Release) + return snap +} + +func (snap *Snapshot) String() string { + return fmt.Sprintf("leveldb.Snapshot{%d}", snap.elem.seq) +} + +// Get gets the value for the given key. It returns ErrNotFound if +// the DB does not contains the key. +// +// The caller should not modify the contents of the returned slice, but +// it is safe to modify the contents of the argument after Get returns. +func (snap *Snapshot) Get(key []byte, ro *opt.ReadOptions) (value []byte, err error) { + err = snap.db.ok() + if err != nil { + return + } + snap.mu.RLock() + defer snap.mu.RUnlock() + if snap.released { + err = ErrSnapshotReleased + return + } + return snap.db.get(nil, nil, key, snap.elem.seq, ro) +} + +// Has returns true if the DB does contains the given key. +// +// It is safe to modify the contents of the argument after Get returns. +func (snap *Snapshot) Has(key []byte, ro *opt.ReadOptions) (ret bool, err error) { + err = snap.db.ok() + if err != nil { + return + } + snap.mu.RLock() + defer snap.mu.RUnlock() + if snap.released { + err = ErrSnapshotReleased + return + } + return snap.db.has(nil, nil, key, snap.elem.seq, ro) +} + +// NewIterator returns an iterator for the snapshot of the underlying DB. +// The returned iterator is not safe for concurrent use, but it is safe to use +// multiple iterators concurrently, with each in a dedicated goroutine. +// It is also safe to use an iterator concurrently with modifying its +// underlying DB. The resultant key/value pairs are guaranteed to be +// consistent. +// +// Slice allows slicing the iterator to only contains keys in the given +// range. A nil Range.Start is treated as a key before all keys in the +// DB. And a nil Range.Limit is treated as a key after all keys in +// the DB. +// +// The iterator must be released after use, by calling Release method. +// Releasing the snapshot doesn't mean releasing the iterator too, the +// iterator would be still valid until released. +// +// Also read Iterator documentation of the leveldb/iterator package. +func (snap *Snapshot) NewIterator(slice *util.Range, ro *opt.ReadOptions) iterator.Iterator { + if err := snap.db.ok(); err != nil { + return iterator.NewEmptyIterator(err) + } + snap.mu.Lock() + defer snap.mu.Unlock() + if snap.released { + return iterator.NewEmptyIterator(ErrSnapshotReleased) + } + // Since iterator already hold version ref, it doesn't need to + // hold snapshot ref. + return snap.db.newIterator(nil, nil, snap.elem.seq, slice, ro) +} + +// Release releases the snapshot. This will not release any returned +// iterators, the iterators would still be valid until released or the +// underlying DB is closed. +// +// Other methods should not be called after the snapshot has been released. +func (snap *Snapshot) Release() { + snap.mu.Lock() + defer snap.mu.Unlock() + + if !snap.released { + // Clear the finalizer. + runtime.SetFinalizer(snap, nil) + + snap.released = true + snap.db.releaseSnapshot(snap.elem) + atomic.AddInt32(&snap.db.aliveSnaps, -1) + snap.db = nil + snap.elem = nil + } +} |