1 files changed, 83 insertions, 65 deletions
diff --git a/Godeps/_workspace/src/github.com/syndtr/goleveldb/leveldb/db_snapshot.go b/Godeps/_workspace/src/github.com/syndtr/goleveldb/leveldb/db_snapshot.go
index 225b7cd5e..0372848ff 100644
--- a/Godeps/_workspace/src/github.com/syndtr/goleveldb/leveldb/db_snapshot.go
+++ b/Godeps/_workspace/src/github.com/syndtr/goleveldb/leveldb/db_snapshot.go
@@ -7,8 +7,11 @@
 package leveldb
 
 import (
+	"container/list"
+	"fmt"
 	"runtime"
 	"sync"
+	"sync/atomic"
 
 	"github.com/syndtr/goleveldb/leveldb/iterator"
 	"github.com/syndtr/goleveldb/leveldb/opt"
@@ -18,51 +21,41 @@ import (
 type snapshotElement struct {
 	seq uint64
 	ref int
-	// Next and previous pointers in the doubly-linked list of elements.
-	next, prev *snapshotElement
-}
-
-// Initialize the snapshot.
-func (db *DB) initSnapshot() {
-	db.snapsRoot.next = &db.snapsRoot
-	db.snapsRoot.prev = &db.snapsRoot
+	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()
-	elem := db.snapsRoot.prev
-	if elem == &db.snapsRoot || elem.seq != seq {
-		at := db.snapsRoot.prev
-		next := at.next
-		elem = &snapshotElement{
-			seq:  seq,
-			prev: at,
-			next: next,
+
+	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")
 		}
-		at.next = elem
-		next.prev = elem
 	}
-	elem.ref++
-	db.snapsMu.Unlock()
-	return elem
+	se := &snapshotElement{seq: seq, ref: 1}
+	se.e = db.snapsList.PushBack(se)
+	return se
 }
 
 // Releases given snapshot element.
-func (db *DB) releaseSnapshot(elem *snapshotElement) {
-	if !db.isClosed() {
-		db.snapsMu.Lock()
-		elem.ref--
-		if elem.ref == 0 {
-			elem.prev.next = elem.next
-			elem.next.prev = elem.prev
-			elem.next = nil
-			elem.prev = nil
-		} else if elem.ref < 0 {
-			panic("leveldb: Snapshot: negative element reference")
-		}
-		db.snapsMu.Unlock()
+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")
 	}
 }
 
@@ -70,10 +63,11 @@ func (db *DB) releaseSnapshot(elem *snapshotElement) {
 func (db *DB) minSeq() uint64 {
 	db.snapsMu.Lock()
 	defer db.snapsMu.Unlock()
-	elem := db.snapsRoot.prev
-	if elem != &db.snapsRoot {
-		return elem.seq
+
+	if e := db.snapsList.Front(); e != nil {
+		return e.Value.(*snapshotElement).seq
 	}
+
 	return db.getSeq()
 }
 
@@ -81,38 +75,59 @@ func (db *DB) minSeq() uint64 {
 type Snapshot struct {
 	db       *DB
 	elem     *snapshotElement
-	mu       sync.Mutex
+	mu       sync.RWMutex
 	released bool
 }
 
 // Creates new snapshot object.
 func (db *DB) newSnapshot() *Snapshot {
-	p := &Snapshot{
+	snap := &Snapshot{
 		db:   db,
 		elem: db.acquireSnapshot(),
 	}
-	runtime.SetFinalizer(p, (*Snapshot).Release)
-	return p
+	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 contain the key.
+// 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 (p *Snapshot) Get(key []byte, ro *opt.ReadOptions) (value []byte, err error) {
-	db := p.db
-	err = db.ok()
+func (snap *Snapshot) Get(key []byte, ro *opt.ReadOptions) (value []byte, err error) {
+	err = snap.db.ok()
 	if err != nil {
 		return
 	}
-	p.mu.Lock()
-	defer p.mu.Unlock()
-	if p.released {
+	snap.mu.RLock()
+	defer snap.mu.RUnlock()
+	if snap.released {
 		err = ErrSnapshotReleased
 		return
 	}
-	return db.get(key, p.elem.seq, ro)
+	return snap.db.get(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(key, snap.elem.seq, ro)
 }
 
 // NewIterator returns an iterator for the snapshot of the uderlying DB.
@@ -132,17 +147,18 @@ func (p *Snapshot) Get(key []byte, ro *opt.ReadOptions) (value []byte, err error
 // iterator would be still valid until released.
 //
 // Also read Iterator documentation of the leveldb/iterator package.
-func (p *Snapshot) NewIterator(slice *util.Range, ro *opt.ReadOptions) iterator.Iterator {
-	db := p.db
-	if err := db.ok(); err != nil {
+func (snap *Snapshot) NewIterator(slice *util.Range, ro *opt.ReadOptions) iterator.Iterator {
+	if err := snap.db.ok(); err != nil {
 		return iterator.NewEmptyIterator(err)
 	}
-	p.mu.Lock()
-	defer p.mu.Unlock()
-	if p.released {
+	snap.mu.Lock()
+	defer snap.mu.Unlock()
+	if snap.released {
 		return iterator.NewEmptyIterator(ErrSnapshotReleased)
 	}
-	return db.newIterator(p.elem.seq, slice, ro)
+	// Since iterator already hold version ref, it doesn't need to
+	// hold snapshot ref.
+	return snap.db.newIterator(snap.elem.seq, slice, ro)
 }
 
 // Release releases the snapshot. This will not release any returned
@@ -150,16 +166,18 @@ func (p *Snapshot) NewIterator(slice *util.Range, ro *opt.ReadOptions) iterator.
 // underlying DB is closed.
 //
 // Other methods should not be called after the snapshot has been released.
-func (p *Snapshot) Release() {
-	p.mu.Lock()
-	if !p.released {
+func (snap *Snapshot) Release() {
+	snap.mu.Lock()
+	defer snap.mu.Unlock()
+
+	if !snap.released {
 		// Clear the finalizer.
-		runtime.SetFinalizer(p, nil)
+		runtime.SetFinalizer(snap, nil)
 
-		p.released = true
-		p.db.releaseSnapshot(p.elem)
-		p.db = nil
-		p.elem = nil
+		snap.released = true
+		snap.db.releaseSnapshot(snap.elem)
+		atomic.AddInt32(&snap.db.aliveSnaps, -1)
+		snap.db = nil
+		snap.elem = nil
 	}
-	p.mu.Unlock()
 }