Cache leveldb stores created from specs (#1975)

go/spec/dataspec.go

@@ -20,6 +20,7 @@ import (
 
 var (
 	datasetRe = regexp.MustCompile("^" + dataset.DatasetRe.String() + "$")
+	ldbStores = map[string]*refCountingLdbStore{}
 )
 
 func GetDatabase(str string) (datas.Database, error) {
@@ -38,7 +39,7 @@ func GetChunkStore(str string) (chunks.ChunkStore, error) {
 
 	switch sp.Protocol {
 	case "ldb":
-		return chunks.NewLevelDBStoreUseFlags(sp.Path, ""), nil
+		return getLDBStore(sp.Path), nil
 	case "mem":
 		return chunks.NewMemoryStore(), nil
 	default:
@@ -173,7 +174,7 @@ func (spec databaseSpec) Database() (ds datas.Database, err error) {
 		}))
 	case "ldb":
 		err = d.Unwrap(d.Try(func() {
-			ds = datas.NewDatabase(chunks.NewLevelDBStoreUseFlags(spec.Path, ""))
+			ds = datas.NewDatabase(getLDBStore(spec.Path))
 		}))
 	case "mem":
 		ds = datas.NewDatabase(chunks.NewMemoryStore())
@@ -225,7 +226,6 @@ func RegisterDatabaseFlags(flags *flag.FlagSet) {
 	chunks.RegisterLevelDBFlags(flags)
 }
 
-// Utility functions to create specs
 func CreateDatabaseSpecString(protocol, path string) string {
 	return fmt.Sprintf("%s:%s", protocol, path)
 }
@@ -233,3 +233,16 @@ func CreateDatabaseSpecString(protocol, path string) string {
 func CreateValueSpecString(protocol, path, value string) string {
 	return fmt.Sprintf("%s:%s::%s", protocol, path, value)
 }
+
+func getLDBStore(path string) chunks.ChunkStore {
+	if store, ok := ldbStores[path]; ok {
+		store.AddRef()
+		return store
+	}
+
+	store := newRefCountingLdbStore(path, func() {
+		delete(ldbStores, path)
+	})
+	ldbStores[path] = store
+	return store
+}

go/spec/ref_counting_ldb_store.go

@@ -0,0 +1,34 @@
+// Copyright 2016 The Noms Authors. All rights reserved.
+// Licensed under the Apache License, version 2.0:
+// http://www.apache.org/licenses/LICENSE-2.0
+
+package spec
+
+import (
+	"github.com/attic-labs/noms/go/chunks"
+	"github.com/attic-labs/noms/go/d"
+)
+
+type refCountingLdbStore struct {
+	*chunks.LevelDBStore
+	refCount int
+	closeFn  func()
+}
+
+func newRefCountingLdbStore(path string, closeFn func()) *refCountingLdbStore {
+	return &refCountingLdbStore{chunks.NewLevelDBStoreUseFlags(path, ""), 1, closeFn}
+}
+
+func (r *refCountingLdbStore) AddRef() {
+	r.refCount++
+}
+
+func (r *refCountingLdbStore) Close() (err error) {
+	d.Chk.True(r.refCount > 0)
+	r.refCount--
+	if r.refCount == 0 {
+		err = r.LevelDBStore.Close()
+		r.closeFn()
+	}
+	return
+}