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snapshot.go
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snapshot.go
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package leveldb
import (
"io"
"runtime"
"github.com/kezhuw/leveldb/internal/errors"
"github.com/kezhuw/leveldb/internal/leveldb"
)
// Snapshot is a readonly and frozen state of LevelDB in particular moment.
type Snapshot struct {
err error
shared *leveldb.Snapshot
}
func newSnapshot(shared *leveldb.Snapshot) *Snapshot {
ss := &Snapshot{shared: shared}
runtime.SetFinalizer(ss, (*Snapshot).finalize)
return ss
}
func (ss *Snapshot) finalize() error {
switch {
case ss.err != nil:
return ss.err
case ss.shared == nil:
return nil
}
shared := ss.shared
ss.shared = nil
shared.Release()
return nil
}
// Snapshot creates a new snapshot from this one. The newly created
// snapshot has independent lifetime as this one.
func (ss *Snapshot) Snapshot() *Snapshot {
switch {
case ss.err != nil:
return &Snapshot{err: ss.err}
case ss.shared == nil:
return &Snapshot{err: errors.ErrSnapshotClosed}
}
ss.shared.Retain()
return newSnapshot(ss.shared)
}
// Dup creates a new snapshot from this one. The newly created
// snapshot has independent lifetime as this one.
//
// Deprecated: Use Snapshot() instead.
func (ss *Snapshot) Dup() *Snapshot {
return ss.Snapshot()
}
// Close releases any resources hold by this snapshot.
func (ss *Snapshot) Close() error {
runtime.SetFinalizer(ss, nil)
return ss.finalize()
}
// Get gets value for given key. It returns ErrNotFound if this snapshot does not
// contain that key.
func (ss *Snapshot) Get(key []byte, opts *ReadOptions) ([]byte, error) {
switch {
case ss.err != nil:
return nil, ss.err
case ss.shared == nil:
return nil, errors.ErrSnapshotClosed
}
return ss.shared.Get(key, convertReadOptions(opts))
}
// All returns an iterator catching all keys in this snapshot.
func (ss *Snapshot) All(opts *ReadOptions) Iterator {
return ss.shared.All(convertReadOptions(opts))
}
// Find returns an iterator catching all keys greater than or equal to start in this snapshot.
// Zero length start acts as infinite small.
func (ss *Snapshot) Find(start []byte, opts *ReadOptions) Iterator {
return ss.shared.Find(start, convertReadOptions(opts))
}
// Range returns an iterator catching all keys between range [start, limit) in this snapshot.
// Zero length start acts as infinite small, zero length limit acts as
// infinite large.
func (ss *Snapshot) Range(start, limit []byte, opts *ReadOptions) Iterator {
return ss.shared.Range(start, limit, convertReadOptions(opts))
}
// Prefix returns an iterator catching all keys having prefix as prefix in this snapshot.
func (ss *Snapshot) Prefix(prefix []byte, opts *ReadOptions) Iterator {
return ss.shared.Prefix(prefix, convertReadOptions(opts))
}
var _ io.Closer = (*Snapshot)(nil)
var _ Reader = (*Snapshot)(nil)