boltdd: return error on use-after-Close

Return the same error as boltdb instead of panic'ing.

helper/boltdd/boltdd.go

@@ -69,6 +69,10 @@ func (db *DB) bucket(btx *bolt.Tx, name []byte) *Bucket {
 	db.rootBucketsLock.Lock()
 	defer db.rootBucketsLock.Unlock()
 
+	if db.isClosed() {
+		return nil
+	}
+
 	b, ok := db.rootBuckets[string(name)]
 	if !ok {
 		b = newBucketMeta()
@@ -87,6 +91,12 @@ func (db *DB) createBucket(btx *bolt.Tx, name []byte) (*Bucket, error) {
 	db.rootBucketsLock.Lock()
 	defer db.rootBucketsLock.Unlock()
 
+	// While creating a bucket on a closed db would error, we must recheck
+	// after acquiring the lock to avoid races.
+	if db.isClosed() {
+		return nil, bolt.ErrDatabaseNotOpen
+	}
+
 	// Always create a new Bucket since CreateBucket above fails if the
 	// bucket already exists.
 	b := newBucketMeta()
@@ -104,6 +114,12 @@ func (db *DB) createBucketIfNotExists(btx *bolt.Tx, name []byte) (*Bucket, error
 	db.rootBucketsLock.Lock()
 	defer db.rootBucketsLock.Unlock()
 
+	// While creating a bucket on a closed db would error, we must recheck
+	// after acquiring the lock to avoid races.
+	if db.isClosed() {
+		return nil, bolt.ErrDatabaseNotOpen
+	}
+
 	b, ok := db.rootBuckets[string(name)]
 	if !ok {
 		b = newBucketMeta()
@@ -127,10 +143,18 @@ func (db *DB) View(fn func(*Tx) error) error {
 	})
 }
 
+// isClosed returns true if the database is closed and must be called while
+// db.rootBucketsLock is acquired.
+func (db *DB) isClosed() bool {
+	return db.rootBuckets == nil
+}
+
 // Close closes the underlying bolt.DB and clears all bucket hashes. DB is
 // unusable after closing.
 func (db *DB) Close() error {
+	db.rootBucketsLock.Lock()
 	db.rootBuckets = nil
+	db.rootBucketsLock.Unlock()
 	return db.bdb.Close()
 }
 

helper/boltdd/boltdd_test.go

@@ -8,6 +8,7 @@ import (
 	"path/filepath"
 	"testing"
 
+	"github.com/boltdb/bolt"
 	"github.com/hashicorp/nomad/nomad/mock"
 	"github.com/hashicorp/nomad/nomad/structs"
 	"github.com/stretchr/testify/require"
@@ -54,6 +55,25 @@ func TestDB_Open(t *testing.T) {
 	require.Equal(0, db.BoltDB().Stats().TxStats.Write)
 }
 
+func TestDB_Close(t *testing.T) {
+	t.Parallel()
+
+	db, cleanup := setupBoltDB(t)
+	defer cleanup()
+
+	db.Close()
+
+	require.Equal(t, db.Update(func(tx *Tx) error {
+		_, err := tx.CreateBucketIfNotExists([]byte("foo"))
+		return err
+	}), bolt.ErrDatabaseNotOpen)
+
+	require.Equal(t, db.Update(func(tx *Tx) error {
+		_, err := tx.CreateBucket([]byte("foo"))
+		return err
+	}), bolt.ErrDatabaseNotOpen)
+}
+
 func TestBucket_Create(t *testing.T) {
 	t.Parallel()
 	require := require.New(t)