storage: wait for compact goroutine to exit before close backend

If backend is closed, the operations on backend in compact
goroutine will panic. So this PR waits for compact goroutine to exit
before close backend.

This fixes the TestWorkflow failure too.

storage/kv_test.go

@@ -44,6 +44,9 @@ func TestWorkflow(t *testing.T) {
 		if err != nil {
 			t.Errorf("#%d: range error (%v)", err)
 		}
+		if len(kvs) != len(wkvs) {
+			t.Fatalf("#%d: len(kvs) = %d, want %d", i, len(kvs), len(wkvs))
+		}
 		for j, kv := range kvs {
 			if !reflect.DeepEqual(kv.Key, wkvs[j].k) {
 				t.Errorf("#%d: keys[%d] = %s, want %s", i, j, kv.Key, wkvs[j].k)

storage/kvstore.go

@@ -39,6 +39,9 @@ type store struct {
 
 	tmu   sync.Mutex // protect the tnxID field
 	tnxID int64      // tracks the current tnxID to verify tnx operations
+
+	wg    sync.WaitGroup
+	stopc chan struct{}
 }
 
 func newStore(path string) *store {
@@ -47,6 +50,7 @@ func newStore(path string) *store {
 		kvindex:        newTreeIndex(),
 		currentRev:     reversion{},
 		compactMainRev: -1,
+		stopc:          make(chan struct{}),
 	}
 
 	tx := s.b.BatchTx()
@@ -161,6 +165,7 @@ func (s *store) Compact(rev int64) error {
 
 	keep := s.kvindex.Compact(rev)
 
+	s.wg.Add(1)
 	go s.scheduleCompaction(rev, keep)
 	return nil
 }
@@ -226,6 +231,9 @@ func (s *store) Restore() error {
 }
 
 func (s *store) Close() error {
+	close(s.stopc)
+	s.wg.Wait()
+	s.b.ForceCommit()
 	return s.b.Close()
 }
 

storage/kvstore_compaction.go

@@ -6,6 +6,7 @@ import (
 )
 
 func (s *store) scheduleCompaction(compactMainRev int64, keep map[reversion]struct{}) {
+	defer s.wg.Done()
 	end := make([]byte, 8)
 	binary.BigEndian.PutUint64(end, uint64(compactMainRev+1))
 
@@ -37,6 +38,10 @@ func (s *store) scheduleCompaction(compactMainRev int64, keep map[reversion]stru
 		revToBytes(reversion{main: rev.main, sub: rev.sub + 1}, last)
 		tx.Unlock()
 
-		time.Sleep(100 * time.Millisecond)
+		select {
+		case <-time.After(100 * time.Millisecond):
+		case <-s.stopc:
+			return
+		}
 	}
 }