make Close methods for the querier safe to call more than once. (#581)

* make Close methods for the querier safe to call more than once.

Signed-off-by: Krasi Georgiev <kgeorgie@redhat.com>

CHANGELOG.md

@@ -1,4 +1,6 @@
 ## master / unreleased
+ - [BUGFIX] Calling `Close` more than once on a querier returns an error instead of a panic.
+
 
 ## 0.7.1
  - [ENHANCEMENT] Reduce memory usage in mergedPostings.Seek

querier.go

@@ -205,6 +205,8 @@ type blockQuerier struct {
 	chunks     ChunkReader
 	tombstones TombstoneReader
 
+	closed bool
+
 	mint, maxt int64
 }
 
@@ -252,12 +254,15 @@ func (q *blockQuerier) LabelValuesFor(string, labels.Label) ([]string, error) {
 }
 
 func (q *blockQuerier) Close() error {
-	var merr tsdb_errors.MultiError
+	if q.closed {
+		return errors.New("block querier already closed")
+	}
 
+	var merr tsdb_errors.MultiError
 	merr.Add(q.index.Close())
 	merr.Add(q.chunks.Close())
 	merr.Add(q.tombstones.Close())
-
+	q.closed = true
 	return merr.Err()
 }
 

querier_test.go

@@ -1898,3 +1898,30 @@ func TestPostingsForMatchers(t *testing.T) {
 	}
 
 }
+
+// TestClose ensures that calling Close more than once doesn't block and doesn't panic.
+func TestClose(t *testing.T) {
+	dir, err := ioutil.TempDir("", "test_storage")
+	if err != nil {
+		t.Fatalf("Opening test dir failed: %s", err)
+	}
+	defer func() {
+		testutil.Ok(t, os.RemoveAll(dir))
+	}()
+
+	createBlock(t, dir, genSeries(1, 1, 0, 10))
+	createBlock(t, dir, genSeries(1, 1, 10, 20))
+
+	db, err := Open(dir, nil, nil, DefaultOptions)
+	if err != nil {
+		t.Fatalf("Opening test storage failed: %s", err)
+	}
+	defer func() {
+		testutil.Ok(t, db.Close())
+	}()
+
+	q, err := db.Querier(0, 20)
+	testutil.Ok(t, err)
+	testutil.Ok(t, q.Close())
+	testutil.NotOk(t, q.Close())
+}

wal/wal.go

@@ -159,9 +159,9 @@ type WAL struct {
 	logger      log.Logger
 	segmentSize int
 	mtx         sync.RWMutex
-	segment     *Segment // active segment
-	donePages   int      // pages written to the segment
-	page        *page    // active page
+	segment     *Segment // Active segment.
+	donePages   int      // Pages written to the segment.
+	page        *page    // Active page.
 	stopc       chan chan struct{}
 	actorc      chan func()
 	closed      bool // To allow calling Close() more than once without blocking.
@@ -606,7 +606,7 @@ func (w *WAL) Close() (err error) {
 	defer w.mtx.Unlock()
 
 	if w.closed {
-		return nil
+		return errors.New("wal already closed")
 	}
 
 	// Flush the last page and zero out all its remaining size.

wal/wal_test.go

@@ -305,6 +305,19 @@ func TestCorruptAndCarryOn(t *testing.T) {
 	}
 }
 
+// TestClose ensures that calling Close more than once doesn't panic and doesn't block.
+func TestClose(t *testing.T) {
+	dir, err := ioutil.TempDir("", "wal_repair")
+	testutil.Ok(t, err)
+	defer func() {
+		testutil.Ok(t, os.RemoveAll(dir))
+	}()
+	w, err := NewSize(nil, nil, dir, pageSize)
+	testutil.Ok(t, err)
+	testutil.Ok(t, w.Close())
+	testutil.NotOk(t, w.Close())
+}
+
 func BenchmarkWAL_LogBatched(b *testing.B) {
 	dir, err := ioutil.TempDir("", "bench_logbatch")
 	testutil.Ok(b, err)