[#642] writecache: Remove usage of close channel in bbolt

Signed-off-by: Anton Nikiforov <an.nikiforov@yadro.com>

pkg/local_object_storage/writecache/writecachebbolt/cachebbolt.go

@@ -30,8 +30,8 @@ type cache struct {
 
 	// flushCh is a channel with objects to flush.
 	flushCh chan objectInfo
-	// closeCh is close channel, protected by modeMtx.
-	closeCh chan struct{}
+	// cancel is cancel function, protected by modeMtx in Close.
+	cancel func()
 	// wg is a wait group for flush workers.
 	wg sync.WaitGroup
 	// store contains underlying database.
@@ -104,17 +104,15 @@ func (c *cache) Open(_ context.Context, readOnly bool) error {
 		return metaerr.Wrap(err)
 	}
 
-	// Opening after Close is done during maintenance mode,
-	// thus we need to create a channel here.
-	c.closeCh = make(chan struct{})
-
 	return metaerr.Wrap(c.initCounters())
 }
 
 // Init runs necessary services.
 func (c *cache) Init() error {
 	c.metrics.SetMode(c.mode)
-	c.runFlushLoop()
+	ctx, cancel := context.WithCancel(context.Background())
+	c.cancel = cancel
+	c.runFlushLoop(ctx)
 	return nil
 }
 
@@ -123,8 +121,9 @@ func (c *cache) Close() error {
 	// We cannot lock mutex for the whole operation duration
 	// because it is taken by some background workers, so `wg.Wait()` is done without modeMtx.
 	c.modeMtx.Lock()
-	if c.closeCh != nil {
-		close(c.closeCh)
+	if c.cancel != nil {
+		c.cancel()
+		c.cancel = nil
 	}
 	c.mode = mode.DegradedReadOnly // prevent new operations from being processed
 	c.modeMtx.Unlock()
@@ -134,7 +133,6 @@ func (c *cache) Close() error {
 	c.modeMtx.Lock()
 	defer c.modeMtx.Unlock()
 
-	c.closeCh = nil
 	var err error
 	if c.db != nil {
 		err = c.db.Close()