Update goleveldb

Godeps/Godeps.json

@@ -48,7 +48,7 @@
 		},
 		{
 			"ImportPath": "github.com/syndtr/goleveldb/leveldb",
-			"Rev": "9bca75c48d6c31becfbb127702b425e7226052e3"
+			"Rev": "e2fa4e6ac1cc41a73bc9fd467878ecbf65df5cc3"
 		},
 		{
 			"ImportPath": "github.com/vitrun/qart/coding",

Godeps/_workspace/src/github.com/syndtr/goleveldb/leveldb/cache/cache_test.go

@@ -7,10 +7,8 @@
 package cache
 
 import (
-	"fmt"
 	"math/rand"
 	"runtime"
-	"strings"
 	"sync"
 	"sync/atomic"
 	"testing"
@@ -225,16 +223,16 @@ func TestLRUCache_Purge(t *testing.T) {
 }
 
 type testingCacheObjectCounter struct {
-	created  uint32
-	released uint32
+	created  uint
+	released uint
 }
 
 func (c *testingCacheObjectCounter) createOne() {
-	atomic.AddUint32(&c.created, 1)
+	c.created++
 }
 
 func (c *testingCacheObjectCounter) releaseOne() {
-	atomic.AddUint32(&c.released, 1)
+	c.released++
 }
 
 type testingCacheObject struct {
@@ -243,17 +241,75 @@ type testingCacheObject struct {
 
 	ns, key uint64
 
-	releaseCalled uint32
+	releaseCalled bool
 }
 
 func (x *testingCacheObject) Release() {
-	if atomic.CompareAndSwapUint32(&x.releaseCalled, 0, 1) {
+	if !x.releaseCalled {
+		x.releaseCalled = true
 		x.cnt.releaseOne()
 	} else {
 		x.t.Errorf("duplicate setfin NS#%d KEY#%s", x.ns, x.key)
 	}
 }
 
+func TestLRUCache_ConcurrentSetGet(t *testing.T) {
+	runtime.GOMAXPROCS(runtime.NumCPU())
+
+	seed := time.Now().UnixNano()
+	t.Logf("seed=%d", seed)
+
+	const (
+		N = 2000000
+		M = 4000
+		C = 3
+	)
+
+	var set, get uint32
+
+	wg := &sync.WaitGroup{}
+	c := NewLRUCache(M / 4)
+	for ni := uint64(0); ni < C; ni++ {
+		r0 := rand.New(rand.NewSource(seed + int64(ni)))
+		r1 := rand.New(rand.NewSource(seed + int64(ni) + 1))
+		ns := c.GetNamespace(ni)
+
+		wg.Add(2)
+		go func(ns Namespace, r *rand.Rand) {
+			for i := 0; i < N; i++ {
+				x := uint64(r.Int63n(M))
+				o := ns.Get(x, func() (int, interface{}) {
+					atomic.AddUint32(&set, 1)
+					return 1, x
+				})
+				if v := o.Value().(uint64); v != x {
+					t.Errorf("#%d invalid value, got=%d", x, v)
+				}
+				o.Release()
+			}
+			wg.Done()
+		}(ns, r0)
+		go func(ns Namespace, r *rand.Rand) {
+			for i := 0; i < N; i++ {
+				x := uint64(r.Int63n(M))
+				o := ns.Get(x, nil)
+				if o != nil {
+					atomic.AddUint32(&get, 1)
+					if v := o.Value().(uint64); v != x {
+						t.Errorf("#%d invalid value, got=%d", x, v)
+					}
+					o.Release()
+				}
+			}
+			wg.Done()
+		}(ns, r1)
+	}
+
+	wg.Wait()
+
+	t.Logf("set=%d get=%d", set, get)
+}
+
 func TestLRUCache_Finalizer(t *testing.T) {
 	const (
 		capacity   = 100
@@ -262,10 +318,6 @@ func TestLRUCache_Finalizer(t *testing.T) {
 		keymax     = 8000
 	)
 
-	runtime.GOMAXPROCS(runtime.NumCPU())
-	defer runtime.GOMAXPROCS(1)
-
-	wg := &sync.WaitGroup{}
 	cnt := &testingCacheObjectCounter{}
 
 	c := NewLRUCache(capacity)
@@ -273,38 +325,40 @@ func TestLRUCache_Finalizer(t *testing.T) {
 	type instance struct {
 		seed       int64
 		rnd        *rand.Rand
-		ns         uint64
-		effective  int32
+		nsid       uint64
+		ns         Namespace
+		effective  int
 		handles    []Handle
 		handlesMap map[uint64]int
 
 		delete          bool
 		purge           bool
 		zap             bool
-		wantDel         int32
-		delfinCalledAll int32
-		delfinCalledEff int32
-		purgefinCalled  int32
+		wantDel         int
+		delfinCalled    int
+		delfinCalledAll int
+		delfinCalledEff int
+		purgefinCalled  int
 	}
 
-	instanceGet := func(p *instance, ns Namespace, key uint64) {
-		h := ns.Get(key, func() (charge int, value interface{}) {
+	instanceGet := func(p *instance, key uint64) {
+		h := p.ns.Get(key, func() (charge int, value interface{}) {
 			to := &testingCacheObject{
 				t: t, cnt: cnt,
-				ns:  p.ns,
+				ns:  p.nsid,
 				key: key,
 			}
-			atomic.AddInt32(&p.effective, 1)
+			p.effective++
 			cnt.createOne()
 			return 1, releaserFunc{func() {
 				to.Release()
-				atomic.AddInt32(&p.effective, -1)
+				p.effective--
 			}, to}
 		})
 		p.handles = append(p.handles, h)
 		p.handlesMap[key] = p.handlesMap[key] + 1
 	}
-	instanceRelease := func(p *instance, ns Namespace, i int) {
+	instanceRelease := func(p *instance, i int) {
 		h := p.handles[i]
 		key := h.Value().(releaserFunc).value.(*testingCacheObject).key
 		if n := p.handlesMap[key]; n == 0 {
@@ -319,55 +373,71 @@ func TestLRUCache_Finalizer(t *testing.T) {
 		p.handles[len(p.handles) : len(p.handles)+1][0] = nil
 	}
 
-	seeds := make([]int64, goroutines)
-	instances := make([]instance, goroutines)
+	seed := time.Now().UnixNano()
+	t.Logf("seed=%d", seed)
+
+	instances := make([]*instance, goroutines)
 	for i := range instances {
-		p := &instances[i]
+		p := &instance{}
 		p.handlesMap = make(map[uint64]int)
-		if seeds[i] == 0 {
-			seeds[i] = time.Now().UnixNano()
-		}
-		p.seed = seeds[i]
+		p.seed = seed + int64(i)
 		p.rnd = rand.New(rand.NewSource(p.seed))
-		p.ns = uint64(i)
+		p.nsid = uint64(i)
+		p.ns = c.GetNamespace(p.nsid)
 		p.delete = i%6 == 0
 		p.purge = i%8 == 0
 		p.zap = i%12 == 0 || i%3 == 0
+		instances[i] = p
 	}
 
-	seedsStr := make([]string, len(seeds))
-	for i, seed := range seeds {
-		seedsStr[i] = fmt.Sprint(seed)
-	}
-	t.Logf("seeds := []int64{%s}", strings.Join(seedsStr, ", "))
-
-	// Get and release.
-	for i := range instances {
-		p := &instances[i]
-
-		wg.Add(1)
-		go func(p *instance) {
-			defer wg.Done()
-
-			ns := c.GetNamespace(p.ns)
-			for i := 0; i < iterations; i++ {
-				if len(p.handles) == 0 || p.rnd.Int()%2 == 0 {
-					instanceGet(p, ns, uint64(p.rnd.Intn(keymax)))
-				} else {
-					instanceRelease(p, ns, p.rnd.Intn(len(p.handles)))
+	runr := rand.New(rand.NewSource(seed - 1))
+	run := func(rnd *rand.Rand, x []*instance, init func(p *instance) bool, fn func(p *instance, i int) bool) {
+		var (
+			rx []*instance
+			rn []int
+		)
+		if init == nil {
+			rx = append([]*instance{}, x...)
+			rn = make([]int, len(x))
+		} else {
+			for _, p := range x {
+				if init(p) {
+					rx = append(rx, p)
+					rn = append(rn, 0)
 				}
 			}
-		}(p)
+		}
+		for len(rx) > 0 {
+			i := rand.Intn(len(rx))
+			if fn(rx[i], rn[i]) {
+				rn[i]++
+			} else {
+				rx = append(rx[:i], rx[i+1:]...)
+				rn = append(rn[:i], rn[i+1:]...)
+			}
+		}
 	}
-	wg.Wait()
+
+	// Get and release.
+	run(runr, instances, nil, func(p *instance, i int) bool {
+		if i < iterations {
+			if len(p.handles) == 0 || p.rnd.Int()%2 == 0 {
+				instanceGet(p, uint64(p.rnd.Intn(keymax)))
+			} else {
+				instanceRelease(p, p.rnd.Intn(len(p.handles)))
+			}
+			return true
+		} else {
+			return false
+		}
+	})
 
 	if used, cap := c.Used(), c.Capacity(); used > cap {
 		t.Errorf("Used > capacity, used=%d cap=%d", used, cap)
 	}
 
 	// Check effective objects.
-	for i := range instances {
-		p := &instances[i]
+	for i, p := range instances {
 		if int(p.effective) < len(p.handlesMap) {
 			t.Errorf("#%d effective objects < acquired handle, eo=%d ah=%d", i, p.effective, len(p.handlesMap))
 		}
@@ -377,103 +447,93 @@ func TestLRUCache_Finalizer(t *testing.T) {
 		t.Errorf("Invalid cache size, want=%d got=%d", want, c.Size())
 	}
 
-	// Delete and purge.
-	for i := range instances {
-		p := &instances[i]
+	// First delete.
+	run(runr, instances, func(p *instance) bool {
 		p.wantDel = p.effective
-
-		wg.Add(1)
-		go func(p *instance) {
-			defer wg.Done()
-
-			ns := c.GetNamespace(p.ns)
-
-			if p.delete {
-				for key := uint64(0); key < keymax; key++ {
-					_, wantExist := p.handlesMap[key]
-					gotExist := ns.Delete(key, func(exist, pending bool) {
-						atomic.AddInt32(&p.delfinCalledAll, 1)
-						if exist {
-							atomic.AddInt32(&p.delfinCalledEff, 1)
-						}
-					})
-					if !gotExist && wantExist {
-						t.Errorf("delete on NS#%d KEY#%d not found", p.ns, key)
-					}
-				}
-
-				var delfinCalled int
-				for key := uint64(0); key < keymax; key++ {
-					func(key uint64) {
-						gotExist := ns.Delete(key, func(exist, pending bool) {
-							if exist && !pending {
-								t.Errorf("delete fin on NS#%d KEY#%d exist and not pending for deletion", p.ns, key)
-							}
-							delfinCalled++
-						})
-						if gotExist {
-							t.Errorf("delete on NS#%d KEY#%d found", p.ns, key)
-						}
-					}(key)
-				}
-				if delfinCalled != keymax {
-					t.Errorf("(2) #%d not all delete fin called, diff=%d", p.ns, keymax-delfinCalled)
+		return p.delete
+	}, func(p *instance, i int) bool {
+		key := uint64(i)
+		if key < keymax {
+			_, wantExist := p.handlesMap[key]
+			gotExist := p.ns.Delete(key, func(exist, pending bool) {
+				p.delfinCalledAll++
+				if exist {
+					p.delfinCalledEff++
 				}
+			})
+			if !gotExist && wantExist {
+				t.Errorf("delete on NS#%d KEY#%d not found", p.nsid, key)
 			}
+			return true
+		} else {
+			return false
+		}
+	})
 
-			if p.purge {
-				ns.Purge(func(ns, key uint64) {
-					atomic.AddInt32(&p.purgefinCalled, 1)
-				})
+	// Second delete.
+	run(runr, instances, func(p *instance) bool {
+		p.delfinCalled = 0
+		return p.delete
+	}, func(p *instance, i int) bool {
+		key := uint64(i)
+		if key < keymax {
+			gotExist := p.ns.Delete(key, func(exist, pending bool) {
+				if exist && !pending {
+					t.Errorf("delete fin on NS#%d KEY#%d exist and not pending for deletion", p.nsid, key)
+				}
+				p.delfinCalled++
+			})
+			if gotExist {
+				t.Errorf("delete on NS#%d KEY#%d found", p.nsid, key)
 			}
-		}(p)
-	}
-	wg.Wait()
+			return true
+		} else {
+			if p.delfinCalled != keymax {
+				t.Errorf("(2) #%d not all delete fin called, diff=%d", p.ns, keymax-p.delfinCalled)
+			}
+			return false
+		}
+	})
+
+	// Purge.
+	run(runr, instances, func(p *instance) bool {
+		return p.purge
+	}, func(p *instance, i int) bool {
+		p.ns.Purge(func(ns, key uint64) {
+			p.purgefinCalled++
+		})
+		return false
+	})
 
 	if want := int(cnt.created - cnt.released); c.Size() != want {
 		t.Errorf("Invalid cache size, want=%d got=%d", want, c.Size())
 	}
 
 	// Release.
-	for i := range instances {
-		p := &instances[i]
-
-		if !p.zap {
-			wg.Add(1)
-			go func(p *instance) {
-				defer wg.Done()
-
-				ns := c.GetNamespace(p.ns)
-				for i := len(p.handles) - 1; i >= 0; i-- {
-					instanceRelease(p, ns, i)
-				}
-			}(p)
+	run(runr, instances, func(p *instance) bool {
+		return !p.zap
+	}, func(p *instance, i int) bool {
+		if len(p.handles) > 0 {
+			instanceRelease(p, len(p.handles)-1)
+			return true
+		} else {
+			return false
 		}
-	}
-	wg.Wait()
+	})
 
 	if want := int(cnt.created - cnt.released); c.Size() != want {
 		t.Errorf("Invalid cache size, want=%d got=%d", want, c.Size())
 	}
 
 	// Zap.
-	for i := range instances {
-		p := &instances[i]
-
-		if p.zap {
-			wg.Add(1)
-			go func(p *instance) {
-				defer wg.Done()
-
-				ns := c.GetNamespace(p.ns)
-				ns.Zap()
-
-				p.handles = nil
-				p.handlesMap = nil
-			}(p)
-		}
-	}
-	wg.Wait()
+	run(runr, instances, func(p *instance) bool {
+		return p.zap
+	}, func(p *instance, i int) bool {
+		p.ns.Zap()
+		p.handles = nil
+		p.handlesMap = nil
+		return false
+	})
 
 	if want := int(cnt.created - cnt.released); c.Size() != want {
 		t.Errorf("Invalid cache size, want=%d got=%d", want, c.Size())
@@ -485,23 +545,21 @@ func TestLRUCache_Finalizer(t *testing.T) {
 
 	c.Purge(nil)
 
-	for i := range instances {
-		p := &instances[i]
-
+	for _, p := range instances {
 		if p.delete {
 			if p.delfinCalledAll != keymax {
-				t.Errorf("#%d not all delete fin called, purge=%v zap=%v diff=%d", p.ns, p.purge, p.zap, keymax-p.delfinCalledAll)
+				t.Errorf("#%d not all delete fin called, purge=%v zap=%v diff=%d", p.nsid, p.purge, p.zap, keymax-p.delfinCalledAll)
 			}
 			if p.delfinCalledEff != p.wantDel {
-				t.Errorf("#%d not all effective delete fin called, diff=%d", p.ns, p.wantDel-p.delfinCalledEff)
+				t.Errorf("#%d not all effective delete fin called, diff=%d", p.nsid, p.wantDel-p.delfinCalledEff)
 			}
 			if p.purge && p.purgefinCalled > 0 {
-				t.Errorf("#%d some purge fin called, delete=%v zap=%v n=%d", p.ns, p.delete, p.zap, p.purgefinCalled)
+				t.Errorf("#%d some purge fin called, delete=%v zap=%v n=%d", p.nsid, p.delete, p.zap, p.purgefinCalled)
 			}
 		} else {
 			if p.purge {
 				if p.purgefinCalled != p.wantDel {
-					t.Errorf("#%d not all purge fin called, delete=%v zap=%v diff=%d", p.ns, p.delete, p.zap, p.wantDel-p.purgefinCalled)
+					t.Errorf("#%d not all purge fin called, delete=%v zap=%v diff=%d", p.nsid, p.delete, p.zap, p.wantDel-p.purgefinCalled)
 				}
 			}
 		}

Godeps/_workspace/src/github.com/syndtr/goleveldb/leveldb/cache/lru_cache.go

@@ -124,6 +124,9 @@ func (c *lruCache) Zap() {
 func (c *lruCache) evict() {
 	top := &c.recent
 	for n := c.recent.rPrev; c.used > c.capacity && n != top; {
+		if n.state != nodeEffective {
+			panic("evicting non effective node")
+		}
 		n.state = nodeEvicted
 		n.rRemove()
 		n.derefNB()
@@ -324,6 +327,10 @@ func (ns *lruNs) Get(key uint64, setf SetFunc) Handle {
 		// Bump to front.
 		n.rRemove()
 		n.rInsert(&ns.lru.recent)
+	case nodeDeleted:
+		// Do nothing.
+	default:
+		panic("invalid state")
 	}
 	n.ref++
 
@@ -472,8 +479,10 @@ func (n *lruNode) fin() {
 		r.Release()
 	}
 	if n.purgefin != nil {
+		if n.delfin != nil {
+			panic("conflicting delete and purge fin")
+		}
 		n.purgefin(n.ns.id, n.key)
-		n.delfin = nil
 		n.purgefin = nil
 	} else if n.delfin != nil {
 		n.delfin(true, false)

Godeps/_workspace/src/github.com/syndtr/goleveldb/leveldb/db_compaction.go

@@ -260,7 +260,7 @@ func (db *DB) memCompaction() {
 		return c.commit(db.journalFile.Num(), db.frozenSeq)
 	}, nil)
 
-	db.logf("mem@flush commited F·%d T·%v", len(c.rec.addedTables), stats.duration)
+	db.logf("mem@flush committed F·%d T·%v", len(c.rec.addedTables), stats.duration)
 
 	for _, r := range c.rec.addedTables {
 		stats.write += r.size
@@ -478,7 +478,7 @@ func (db *DB) tableCompaction(c *compaction, noTrivial bool) {
 	}, nil)
 
 	resultSize := int(stats[1].write)
-	db.logf("table@compaction commited F%s S%s D·%d T·%v", sint(len(rec.addedTables)-len(rec.deletedTables)), sshortenb(resultSize-sourceSize), dropCnt, stats[1].duration)
+	db.logf("table@compaction committed F%s S%s D·%d T·%v", sint(len(rec.addedTables)-len(rec.deletedTables)), sshortenb(resultSize-sourceSize), dropCnt, stats[1].duration)
 
 	// Save compaction stats
 	for i := range stats {

Godeps/_workspace/src/github.com/syndtr/goleveldb/leveldb/db_iter.go

@@ -321,9 +321,13 @@ func (i *dbIter) Release() {
 }
 
 func (i *dbIter) SetReleaser(releaser util.Releaser) {
-	if i.dir != dirReleased {
-		i.releaser = releaser
+	if i.dir == dirReleased {
+		panic(util.ErrReleased)
 	}
+	if i.releaser != nil && releaser != nil {
+		panic(util.ErrHasReleaser)
+	}
+	i.releaser = releaser
 }
 
 func (i *dbIter) Error() error {

Godeps/_workspace/src/github.com/syndtr/goleveldb/leveldb/db_test.go

@@ -1577,11 +1577,7 @@ func TestDb_BloomFilter(t *testing.T) {
 		return fmt.Sprintf("key%06d", i)
 	}
 
-	const (
-		n              = 10000
-		indexOverhead  = 19898
-		filterOverhead = 19799
-	)
+	const n = 10000
 
 	// Populate multiple layers
 	for i := 0; i < n; i++ {
@@ -1605,7 +1601,7 @@ func TestDb_BloomFilter(t *testing.T) {
 	cnt := int(h.stor.ReadCounter())
 	t.Logf("lookup of %d present keys yield %d sstable I/O reads", n, cnt)
 
-	if min, max := n+indexOverhead+filterOverhead, n+indexOverhead+filterOverhead+2*n/100; cnt < min || cnt > max {
+	if min, max := n, n+2*n/100; cnt < min || cnt > max {
 		t.Errorf("num of sstable I/O reads of present keys not in range of %d - %d, got %d", min, max, cnt)
 	}
 
@@ -1616,7 +1612,7 @@ func TestDb_BloomFilter(t *testing.T) {
 	}
 	cnt = int(h.stor.ReadCounter())
 	t.Logf("lookup of %d missing keys yield %d sstable I/O reads", n, cnt)
-	if max := 3*n/100 + indexOverhead + filterOverhead; cnt > max {
+	if max := 3 * n / 100; cnt > max {
 		t.Errorf("num of sstable I/O reads of missing keys was more than %d, got %d", max, cnt)
 	}
 

Godeps/_workspace/src/github.com/syndtr/goleveldb/leveldb/iterator/array_iter.go

@@ -40,13 +40,19 @@ type basicArrayIterator struct {
 	util.BasicReleaser
 	array BasicArray
 	pos   int
+	err   error
 }
 
 func (i *basicArrayIterator) Valid() bool {
-	return i.pos >= 0 && i.pos < i.array.Len()
+	return i.pos >= 0 && i.pos < i.array.Len() && !i.Released()
 }
 
 func (i *basicArrayIterator) First() bool {
+	if i.Released() {
+		i.err = ErrIterReleased
+		return false
+	}
+
 	if i.array.Len() == 0 {
 		i.pos = -1
 		return false
@@ -56,6 +62,11 @@ func (i *basicArrayIterator) First() bool {
 }
 
 func (i *basicArrayIterator) Last() bool {
+	if i.Released() {
+		i.err = ErrIterReleased
+		return false
+	}
+
 	n := i.array.Len()
 	if n == 0 {
 		i.pos = 0
@@ -66,6 +77,11 @@ func (i *basicArrayIterator) Last() bool {
 }
 
 func (i *basicArrayIterator) Seek(key []byte) bool {
+	if i.Released() {
+		i.err = ErrIterReleased
+		return false
+	}
+
 	n := i.array.Len()
 	if n == 0 {
 		i.pos = 0
@@ -79,6 +95,11 @@ func (i *basicArrayIterator) Seek(key []byte) bool {
 }
 
 func (i *basicArrayIterator) Next() bool {
+	if i.Released() {
+		i.err = ErrIterReleased
+		return false
+	}
+
 	i.pos++
 	if n := i.array.Len(); i.pos >= n {
 		i.pos = n
@@ -88,6 +109,11 @@ func (i *basicArrayIterator) Next() bool {
 }
 
 func (i *basicArrayIterator) Prev() bool {
+	if i.Released() {
+		i.err = ErrIterReleased
+		return false
+	}
+
 	i.pos--
 	if i.pos < 0 {
 		i.pos = -1
@@ -96,7 +122,7 @@ func (i *basicArrayIterator) Prev() bool {
 	return true
 }
 
-func (i *basicArrayIterator) Error() error { return nil }
+func (i *basicArrayIterator) Error() error { return i.err }
 
 type arrayIterator struct {
 	basicArrayIterator

Godeps/_workspace/src/github.com/syndtr/goleveldb/leveldb/iterator/indexed_iter.go

@@ -26,9 +26,10 @@ type indexedIterator struct {
 	strict    bool
 	strictGet bool
 
-	data Iterator
-	err  error
-	errf func(err error)
+	data   Iterator
+	err    error
+	errf   func(err error)
+	closed bool
 }
 
 func (i *indexedIterator) setData() {
@@ -50,6 +51,15 @@ func (i *indexedIterator) clearData() {
 	i.data = nil
 }
 
+func (i *indexedIterator) indexErr() {
+	if err := i.index.Error(); err != nil {
+		if i.errf != nil {
+			i.errf(err)
+		}
+		i.err = err
+	}
+}
+
 func (i *indexedIterator) dataErr() bool {
 	if i.errf != nil {
 		if err := i.data.Error(); err != nil {
@@ -72,9 +82,13 @@ func (i *indexedIterator) Valid() bool {
 func (i *indexedIterator) First() bool {
 	if i.err != nil {
 		return false
+	} else if i.Released() {
+		i.err = ErrIterReleased
+		return false
 	}
 
 	if !i.index.First() {
+		i.indexErr()
 		i.clearData()
 		return false
 	}
@@ -85,9 +99,13 @@ func (i *indexedIterator) First() bool {
 func (i *indexedIterator) Last() bool {
 	if i.err != nil {
 		return false
+	} else if i.Released() {
+		i.err = ErrIterReleased
+		return false
 	}
 
 	if !i.index.Last() {
+		i.indexErr()
 		i.clearData()
 		return false
 	}
@@ -105,9 +123,13 @@ func (i *indexedIterator) Last() bool {
 func (i *indexedIterator) Seek(key []byte) bool {
 	if i.err != nil {
 		return false
+	} else if i.Released() {
+		i.err = ErrIterReleased
+		return false
 	}
 
 	if !i.index.Seek(key) {
+		i.indexErr()
 		i.clearData()
 		return false
 	}
@@ -125,6 +147,9 @@ func (i *indexedIterator) Seek(key []byte) bool {
 func (i *indexedIterator) Next() bool {
 	if i.err != nil {
 		return false
+	} else if i.Released() {
+		i.err = ErrIterReleased
+		return false
 	}
 
 	switch {
@@ -136,6 +161,7 @@ func (i *indexedIterator) Next() bool {
 		fallthrough
 	case i.data == nil:
 		if !i.index.Next() {
+			i.indexErr()
 			return false
 		}
 		i.setData()
@@ -147,6 +173,9 @@ func (i *indexedIterator) Next() bool {
 func (i *indexedIterator) Prev() bool {
 	if i.err != nil {
 		return false
+	} else if i.Released() {
+		i.err = ErrIterReleased
+		return false
 	}
 
 	switch {
@@ -158,6 +187,7 @@ func (i *indexedIterator) Prev() bool {
 		fallthrough
 	case i.data == nil:
 		if !i.index.Prev() {
+			i.indexErr()
 			return false
 		}
 		i.setData()

Godeps/_workspace/src/github.com/syndtr/goleveldb/leveldb/iterator/iter.go

@@ -14,6 +14,10 @@ import (
 	"github.com/syndtr/goleveldb/leveldb/util"
 )
 
+var (
+	ErrIterReleased = errors.New("leveldb/iterator: iterator released")
+)
+
 // IteratorSeeker is the interface that wraps the 'seeks method'.
 type IteratorSeeker interface {
 	// First moves the iterator to the first key/value pair. If the iterator
@@ -100,28 +104,13 @@ type ErrorCallbackSetter interface {
 }
 
 type emptyIterator struct {
-	releaser util.Releaser
-	released bool
-	err      error
+	util.BasicReleaser
+	err error
 }
 
 func (i *emptyIterator) rErr() {
-	if i.err == nil && i.released {
-		i.err = errors.New("leveldb/iterator: iterator released")
-	}
-}
-
-func (i *emptyIterator) Release() {
-	if i.releaser != nil {
-		i.releaser.Release()
-		i.releaser = nil
-	}
-	i.released = true
-}
-
-func (i *emptyIterator) SetReleaser(releaser util.Releaser) {
-	if !i.released {
-		i.releaser = releaser
+	if i.err == nil && i.Released() {
+		i.err = ErrIterReleased
 	}
 }
 

Godeps/_workspace/src/github.com/syndtr/goleveldb/leveldb/iterator/merged_iter.go

@@ -7,16 +7,10 @@
 package iterator
 
 import (
-	"errors"
-
 	"github.com/syndtr/goleveldb/leveldb/comparer"
 	"github.com/syndtr/goleveldb/leveldb/util"
 )
 
-var (
-	ErrIterReleased = errors.New("leveldb/iterator: iterator released")
-)
-
 type dir int
 
 const (
@@ -274,9 +268,13 @@ func (i *mergedIterator) Release() {
 }
 
 func (i *mergedIterator) SetReleaser(releaser util.Releaser) {
-	if i.dir != dirReleased {
-		i.releaser = releaser
+	if i.dir == dirReleased {
+		panic(util.ErrReleased)
 	}
+	if i.releaser != nil && releaser != nil {
+		panic(util.ErrHasReleaser)
+	}
+	i.releaser = releaser
 }
 
 func (i *mergedIterator) Error() error {

Godeps/_workspace/src/github.com/syndtr/goleveldb/leveldb/memdb/memdb.go

@@ -8,6 +8,7 @@
 package memdb
 
 import (
+	"errors"
 	"math/rand"
 	"sync"
 
@@ -17,7 +18,8 @@ import (
 )
 
 var (
-	ErrNotFound = util.ErrNotFound
+	ErrNotFound     = util.ErrNotFound
+	ErrIterReleased = errors.New("leveldb/memdb: iterator released")
 )
 
 const tMaxHeight = 12
@@ -29,6 +31,7 @@ type dbIter struct {
 	node       int
 	forward    bool
 	key, value []byte
+	err        error
 }
 
 func (i *dbIter) fill(checkStart, checkLimit bool) bool {
@@ -59,6 +62,11 @@ func (i *dbIter) Valid() bool {
 }
 
 func (i *dbIter) First() bool {
+	if i.Released() {
+		i.err = ErrIterReleased
+		return false
+	}
+
 	i.forward = true
 	i.p.mu.RLock()
 	defer i.p.mu.RUnlock()
@@ -71,9 +79,11 @@ func (i *dbIter) First() bool {
 }
 
 func (i *dbIter) Last() bool {
-	if i.p == nil {
+	if i.Released() {
+		i.err = ErrIterReleased
 		return false
 	}
+
 	i.forward = false
 	i.p.mu.RLock()
 	defer i.p.mu.RUnlock()
@@ -86,9 +96,11 @@ func (i *dbIter) Last() bool {
 }
 
 func (i *dbIter) Seek(key []byte) bool {
-	if i.p == nil {
+	if i.Released() {
+		i.err = ErrIterReleased
 		return false
 	}
+
 	i.forward = true
 	i.p.mu.RLock()
 	defer i.p.mu.RUnlock()
@@ -100,9 +112,11 @@ func (i *dbIter) Seek(key []byte) bool {
 }
 
 func (i *dbIter) Next() bool {
-	if i.p == nil {
+	if i.Released() {
+		i.err = ErrIterReleased
 		return false
 	}
+
 	if i.node == 0 {
 		if !i.forward {
 			return i.First()
@@ -117,9 +131,11 @@ func (i *dbIter) Next() bool {
 }
 
 func (i *dbIter) Prev() bool {
-	if i.p == nil {
+	if i.Released() {
+		i.err = ErrIterReleased
 		return false
 	}
+
 	if i.node == 0 {
 		if i.forward {
 			return i.Last()
@@ -141,10 +157,10 @@ func (i *dbIter) Value() []byte {
 	return i.value
 }
 
-func (i *dbIter) Error() error { return nil }
+func (i *dbIter) Error() error { return i.err }
 
 func (i *dbIter) Release() {
-	if i.p != nil {
+	if !i.Released() {
 		i.p = nil
 		i.node = 0
 		i.key = nil

Godeps/_workspace/src/github.com/syndtr/goleveldb/leveldb/session_util.go

@@ -147,7 +147,7 @@ func (s *session) fillRecord(r *sessionRecord, snapshot bool) {
 	}
 }
 
-// Mark if record has been commited, this will update session state;
+// Mark if record has been committed, this will update session state;
 // need external synchronization.
 func (s *session) recordCommited(r *sessionRecord) {
 	if r.has(recJournalNum) {

Godeps/_workspace/src/github.com/syndtr/goleveldb/leveldb/table.go

@@ -7,7 +7,9 @@
 package leveldb
 
 import (
+	"fmt"
 	"sort"
+	"sync"
 	"sync/atomic"
 
 	"github.com/syndtr/goleveldb/leveldb/cache"
@@ -276,6 +278,8 @@ type tOps struct {
 	cache   cache.Cache
 	cacheNS cache.Namespace
 	bpool   *util.BufferPool
+	mu      sync.Mutex
+	closed  bool
 }
 
 // Creates an empty table and returns table writer.
@@ -322,9 +326,42 @@ func (t *tOps) createFrom(src iterator.Iterator) (f *tFile, n int, err error) {
 	return
 }
 
+type trWrapper struct {
+	*table.Reader
+	t   *tOps
+	ref int
+}
+
+func (w *trWrapper) Release() {
+	if w.ref != 0 && !w.t.closed {
+		panic(fmt.Sprintf("BUG: invalid ref %d, refer to issue #72", w.ref))
+	}
+	w.Reader.Release()
+}
+
+type trCacheHandleWrapper struct {
+	cache.Handle
+	t        *tOps
+	released bool
+}
+
+func (w *trCacheHandleWrapper) Release() {
+	w.t.mu.Lock()
+	defer w.t.mu.Unlock()
+
+	if !w.released {
+		w.released = true
+		w.Value().(*trWrapper).ref--
+	}
+	w.Handle.Release()
+}
+
 // Opens table. It returns a cache handle, which should
 // be released after use.
 func (t *tOps) open(f *tFile) (ch cache.Handle, err error) {
+	t.mu.Lock()
+	defer t.mu.Unlock()
+
 	num := f.file.Num()
 	ch = t.cacheNS.Get(num, func() (charge int, value interface{}) {
 		var r storage.Reader
@@ -337,11 +374,13 @@ func (t *tOps) open(f *tFile) (ch cache.Handle, err error) {
 		if bc := t.s.o.GetBlockCache(); bc != nil {
 			bcacheNS = bc.GetNamespace(num)
 		}
-		return 1, table.NewReader(r, int64(f.size), bcacheNS, t.bpool, t.s.o)
+		return 1, &trWrapper{table.NewReader(r, int64(f.size), bcacheNS, t.bpool, t.s.o), t, 0}
 	})
 	if ch == nil && err == nil {
 		err = ErrClosed
 	}
+	ch.Value().(*trWrapper).ref++
+	ch = &trCacheHandleWrapper{ch, t, false}
 	return
 }
 
@@ -353,7 +392,7 @@ func (t *tOps) find(f *tFile, key []byte, ro *opt.ReadOptions) (rkey, rvalue []b
 		return nil, nil, err
 	}
 	defer ch.Release()
-	return ch.Value().(*table.Reader).Find(key, ro)
+	return ch.Value().(*trWrapper).Find(key, ro)
 }
 
 // Returns approximate offset of the given key.
@@ -363,7 +402,7 @@ func (t *tOps) offsetOf(f *tFile, key []byte) (offset uint64, err error) {
 		return
 	}
 	defer ch.Release()
-	offset_, err := ch.Value().(*table.Reader).OffsetOf(key)
+	offset_, err := ch.Value().(*trWrapper).OffsetOf(key)
 	return uint64(offset_), err
 }
 
@@ -373,7 +412,7 @@ func (t *tOps) newIterator(f *tFile, slice *util.Range, ro *opt.ReadOptions) ite
 	if err != nil {
 		return iterator.NewEmptyIterator(err)
 	}
-	iter := ch.Value().(*table.Reader).NewIterator(slice, ro)
+	iter := ch.Value().(*trWrapper).NewIterator(slice, ro)
 	iter.SetReleaser(ch)
 	return iter
 }
@@ -381,6 +420,9 @@ func (t *tOps) newIterator(f *tFile, slice *util.Range, ro *opt.ReadOptions) ite
 // Removes table from persistent storage. It waits until
 // no one use the the table.
 func (t *tOps) remove(f *tFile) {
+	t.mu.Lock()
+	defer t.mu.Unlock()
+
 	num := f.file.Num()
 	t.cacheNS.Delete(num, func(exist, pending bool) {
 		if !pending {
@@ -399,6 +441,10 @@ func (t *tOps) remove(f *tFile) {
 // Closes the table ops instance. It will close all tables,
 // regadless still used or not.
 func (t *tOps) close() {
+	t.mu.Lock()
+	defer t.mu.Unlock()
+
+	t.closed = true
 	t.cache.Zap()
 	t.bpool.Close()
 }

Godeps/_workspace/src/github.com/syndtr/goleveldb/leveldb/table/reader.go

@@ -13,6 +13,7 @@ import (
 	"io"
 	"sort"
 	"strings"
+	"sync"
 
 	"code.google.com/p/snappy-go/snappy"
 
@@ -25,8 +26,9 @@ import (
 )
 
 var (
-	ErrNotFound     = util.ErrNotFound
-	ErrIterReleased = errors.New("leveldb/table: iterator released")
+	ErrNotFound       = util.ErrNotFound
+	ErrReaderReleased = errors.New("leveldb/table: reader released")
+	ErrIterReleased   = errors.New("leveldb/table: iterator released")
 )
 
 func max(x, y int) int {
@@ -134,9 +136,7 @@ func (b *block) newIterator(slice *util.Range, inclLimit bool, cache util.Releas
 }
 
 func (b *block) Release() {
-	if b.tr.bpool != nil {
-		b.tr.bpool.Put(b.data)
-	}
+	b.tr.bpool.Put(b.data)
 	b.tr = nil
 	b.data = nil
 }
@@ -439,7 +439,7 @@ func (i *blockIter) Value() []byte {
 }
 
 func (i *blockIter) Release() {
-	if i.dir > dirReleased {
+	if i.dir != dirReleased {
 		i.block = nil
 		i.prevNode = nil
 		i.prevKeys = nil
@@ -458,9 +458,13 @@ func (i *blockIter) Release() {
 }
 
 func (i *blockIter) SetReleaser(releaser util.Releaser) {
-	if i.dir > dirReleased {
-		i.releaser = releaser
+	if i.dir == dirReleased {
+		panic(util.ErrReleased)
 	}
+	if i.releaser != nil && releaser != nil {
+		panic(util.ErrHasReleaser)
+	}
+	i.releaser = releaser
 }
 
 func (i *blockIter) Valid() bool {
@@ -495,9 +499,7 @@ func (b *filterBlock) contains(offset uint64, key []byte) bool {
 }
 
 func (b *filterBlock) Release() {
-	if b.tr.bpool != nil {
-		b.tr.bpool.Put(b.data)
-	}
+	b.tr.bpool.Put(b.data)
 	b.tr = nil
 	b.data = nil
 }
@@ -519,15 +521,17 @@ func (i *indexIter) Get() iterator.Iterator {
 	if n == 0 {
 		return iterator.NewEmptyIterator(errors.New("leveldb/table: Reader: invalid table (bad data block handle)"))
 	}
+
 	var slice *util.Range
 	if i.slice != nil && (i.blockIter.isFirst() || i.blockIter.isLast()) {
 		slice = i.slice
 	}
-	return i.blockIter.block.tr.getDataIter(dataBH, slice, i.checksum, i.fillCache)
+	return i.blockIter.block.tr.getDataIterErr(dataBH, slice, i.checksum, i.fillCache)
 }
 
 // Reader is a table reader.
 type Reader struct {
+	mu     sync.RWMutex
 	reader io.ReaderAt
 	cache  cache.Namespace
 	err    error
@@ -540,6 +544,8 @@ type Reader struct {
 
 	dataEnd           int64
 	indexBH, filterBH blockHandle
+	indexBlock        *block
+	filterBlock       *filterBlock
 }
 
 func verifyChecksum(data []byte) bool {
@@ -688,6 +694,20 @@ func (r *Reader) readFilterBlockCached(bh blockHandle, fillCache bool) (*filterB
 	return b, b, err
 }
 
+func (r *Reader) getIndexBlock(fillCache bool) (b *block, rel util.Releaser, err error) {
+	if r.indexBlock == nil {
+		return r.readBlockCached(r.indexBH, true, fillCache)
+	}
+	return r.indexBlock, util.NoopReleaser{}, nil
+}
+
+func (r *Reader) getFilterBlock(fillCache bool) (*filterBlock, util.Releaser, error) {
+	if r.filterBlock == nil {
+		return r.readFilterBlockCached(r.filterBH, fillCache)
+	}
+	return r.filterBlock, util.NoopReleaser{}, nil
+}
+
 func (r *Reader) getDataIter(dataBH blockHandle, slice *util.Range, checksum, fillCache bool) iterator.Iterator {
 	b, rel, err := r.readBlockCached(dataBH, checksum, fillCache)
 	if err != nil {
@@ -696,6 +716,17 @@ func (r *Reader) getDataIter(dataBH blockHandle, slice *util.Range, checksum, fi
 	return b.newIterator(slice, false, rel)
 }
 
+func (r *Reader) getDataIterErr(dataBH blockHandle, slice *util.Range, checksum, fillCache bool) iterator.Iterator {
+	r.mu.RLock()
+	defer r.mu.RUnlock()
+
+	if r.err != nil {
+		return iterator.NewEmptyIterator(r.err)
+	}
+
+	return r.getDataIter(dataBH, slice, checksum, fillCache)
+}
+
 // NewIterator creates an iterator from the table.
 //
 // Slice allows slicing the iterator to only contains keys in the given
@@ -708,22 +739,25 @@ func (r *Reader) getDataIter(dataBH blockHandle, slice *util.Range, checksum, fi
 //
 // Also read Iterator documentation of the leveldb/iterator package.
 func (r *Reader) NewIterator(slice *util.Range, ro *opt.ReadOptions) iterator.Iterator {
+	r.mu.RLock()
+	defer r.mu.RUnlock()
+
 	if r.err != nil {
 		return iterator.NewEmptyIterator(r.err)
 	}
 
 	fillCache := !ro.GetDontFillCache()
-	b, rel, err := r.readBlockCached(r.indexBH, true, fillCache)
+	indexBlock, rel, err := r.getIndexBlock(fillCache)
 	if err != nil {
 		return iterator.NewEmptyIterator(err)
 	}
 	index := &indexIter{
-		blockIter: b.newIterator(slice, true, rel),
+		blockIter: indexBlock.newIterator(slice, true, rel),
 		slice:     slice,
 		checksum:  ro.GetStrict(opt.StrictBlockChecksum),
 		fillCache: !ro.GetDontFillCache(),
 	}
-	return iterator.NewIndexedIterator(index, r.strictIter || ro.GetStrict(opt.StrictIterator), false)
+	return iterator.NewIndexedIterator(index, r.strictIter || ro.GetStrict(opt.StrictIterator), true)
 }
 
 // Find finds key/value pair whose key is greater than or equal to the
@@ -733,12 +767,15 @@ func (r *Reader) NewIterator(slice *util.Range, ro *opt.ReadOptions) iterator.It
 // The caller should not modify the contents of the returned slice, but
 // it is safe to modify the contents of the argument after Find returns.
 func (r *Reader) Find(key []byte, ro *opt.ReadOptions) (rkey, value []byte, err error) {
+	r.mu.RLock()
+	defer r.mu.RUnlock()
+
 	if r.err != nil {
 		err = r.err
 		return
 	}
 
-	indexBlock, rel, err := r.readBlockCached(r.indexBH, true, true)
+	indexBlock, rel, err := r.getIndexBlock(true)
 	if err != nil {
 		return
 	}
@@ -759,7 +796,7 @@ func (r *Reader) Find(key []byte, ro *opt.ReadOptions) (rkey, value []byte, err
 		return
 	}
 	if r.filter != nil {
-		filterBlock, rel, ferr := r.readFilterBlockCached(r.filterBH, true)
+		filterBlock, rel, ferr := r.getFilterBlock(true)
 		if ferr == nil {
 			if !filterBlock.contains(dataBH.offset, key) {
 				rel.Release()
@@ -779,9 +816,13 @@ func (r *Reader) Find(key []byte, ro *opt.ReadOptions) (rkey, value []byte, err
 	}
 	// Don't use block buffer, no need to copy the buffer.
 	rkey = data.Key()
-	// Use block buffer, and since the buffer will be recycled, the buffer
-	// need to be copied.
-	value = append([]byte{}, data.Value()...)
+	if r.bpool == nil {
+		value = data.Value()
+	} else {
+		// Use block buffer, and since the buffer will be recycled, the buffer
+		// need to be copied.
+		value = append([]byte{}, data.Value()...)
+	}
 	return
 }
 
@@ -791,6 +832,9 @@ func (r *Reader) Find(key []byte, ro *opt.ReadOptions) (rkey, value []byte, err
 // 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 (r *Reader) Get(key []byte, ro *opt.ReadOptions) (value []byte, err error) {
+	r.mu.RLock()
+	defer r.mu.RUnlock()
+
 	if r.err != nil {
 		err = r.err
 		return
@@ -808,6 +852,9 @@ func (r *Reader) Get(key []byte, ro *opt.ReadOptions) (value []byte, err error)
 //
 // It is safe to modify the contents of the argument after Get returns.
 func (r *Reader) OffsetOf(key []byte) (offset int64, err error) {
+	r.mu.RLock()
+	defer r.mu.RUnlock()
+
 	if r.err != nil {
 		err = r.err
 		return
@@ -840,12 +887,24 @@ func (r *Reader) OffsetOf(key []byte) (offset int64, err error) {
 // Release implements util.Releaser.
 // It also close the file if it is an io.Closer.
 func (r *Reader) Release() {
+	r.mu.Lock()
+	defer r.mu.Unlock()
+
 	if closer, ok := r.reader.(io.Closer); ok {
 		closer.Close()
 	}
+	if r.indexBlock != nil {
+		r.indexBlock.Release()
+		r.indexBlock = nil
+	}
+	if r.filterBlock != nil {
+		r.filterBlock.Release()
+		r.filterBlock = nil
+	}
 	r.reader = nil
 	r.cache = nil
 	r.bpool = nil
+	r.err = ErrReaderReleased
 }
 
 // NewReader creates a new initialized table reader for the file.
@@ -853,9 +912,6 @@ func (r *Reader) Release() {
 //
 // The returned table reader instance is goroutine-safe.
 func NewReader(f io.ReaderAt, size int64, cache cache.Namespace, bpool *util.BufferPool, o *opt.Options) *Reader {
-	if bpool == nil {
-		bpool = util.NewBufferPool(o.GetBlockSize() + blockTrailerLen)
-	}
 	r := &Reader{
 		reader:     f,
 		cache:      cache,
@@ -930,5 +986,22 @@ func NewReader(f io.ReaderAt, size int64, cache cache.Namespace, bpool *util.Buf
 	}
 	metaIter.Release()
 	metaBlock.Release()
+
+	// Cache index and filter block locally, since we don't have global cache.
+	if cache == nil {
+		r.indexBlock, r.err = r.readBlock(r.indexBH, true)
+		if r.err != nil {
+			return r
+		}
+		if r.filter != nil {
+			r.filterBlock, err = r.readFilterBlock(r.filterBH)
+			if err != nil {
+				// Don't use filter then.
+				r.filter = nil
+				r.filterBH = blockHandle{}
+			}
+		}
+	}
+
 	return r
 }

Godeps/_workspace/src/github.com/syndtr/goleveldb/leveldb/util/buffer_pool.go

@@ -54,6 +54,10 @@ func (p *BufferPool) poolNum(n int) int {
 
 // Get returns buffer with length of n.
 func (p *BufferPool) Get(n int) []byte {
+	if p == nil {
+		return make([]byte, n)
+	}
+
 	atomic.AddUint32(&p.get, 1)
 
 	poolNum := p.poolNum(n)
@@ -145,6 +149,10 @@ func (p *BufferPool) Get(n int) []byte {
 
 // Put adds given buffer to the pool.
 func (p *BufferPool) Put(b []byte) {
+	if p == nil {
+		return
+	}
+
 	atomic.AddUint32(&p.put, 1)
 
 	pool := p.pool[p.poolNum(cap(b))]
@@ -156,6 +164,10 @@ func (p *BufferPool) Put(b []byte) {
 }
 
 func (p *BufferPool) Close() {
+	if p == nil {
+		return
+	}
+
 	select {
 	case p.close <- struct{}{}:
 	default:
@@ -163,6 +175,10 @@ func (p *BufferPool) Close() {
 }
 
 func (p *BufferPool) String() string {
+	if p == nil {
+		return "<nil>"
+	}
+
 	return fmt.Sprintf("BufferPool{B·%d Z·%v Zm·%v Zh·%v G·%d P·%d H·%d <·%d =·%d >·%d M·%d}",
 		p.baseline0, p.size, p.sizeMiss, p.sizeHalf, p.get, p.put, p.half, p.less, p.equal, p.greater, p.miss)
 }

Godeps/_workspace/src/github.com/syndtr/goleveldb/leveldb/util/util.go

@@ -12,7 +12,9 @@ import (
 )
 
 var (
-	ErrNotFound = errors.New("leveldb: not found")
+	ErrNotFound    = errors.New("leveldb: not found")
+	ErrReleased    = errors.New("leveldb: resource already relesed")
+	ErrHasReleaser = errors.New("leveldb: releaser already defined")
 )
 
 // Releaser is the interface that wraps the basic Release method.
@@ -27,23 +29,46 @@ type ReleaseSetter interface {
 	// SetReleaser associates the given releaser to the resources. The
 	// releaser will be called once coresponding resources released.
 	// Calling SetReleaser with nil will clear the releaser.
+	//
+	// This will panic if a releaser already present or coresponding
+	// resource is already released. Releaser should be cleared first
+	// before assigned a new one.
 	SetReleaser(releaser Releaser)
 }
 
 // BasicReleaser provides basic implementation of Releaser and ReleaseSetter.
 type BasicReleaser struct {
 	releaser Releaser
+	released bool
+}
+
+// Released returns whether Release method already called.
+func (r *BasicReleaser) Released() bool {
+	return r.released
 }
 
 // Release implements Releaser.Release.
 func (r *BasicReleaser) Release() {
-	if r.releaser != nil {
-		r.releaser.Release()
-		r.releaser = nil
+	if !r.released {
+		if r.releaser != nil {
+			r.releaser.Release()
+			r.releaser = nil
+		}
+		r.released = true
 	}
 }
 
 // SetReleaser implements ReleaseSetter.SetReleaser.
 func (r *BasicReleaser) SetReleaser(releaser Releaser) {
+	if r.released {
+		panic(ErrReleased)
+	}
+	if r.releaser != nil && releaser != nil {
+		panic(ErrHasReleaser)
+	}
 	r.releaser = releaser
 }
+
+type NoopReleaser struct{}
+
+func (NoopReleaser) Release() {}