From 559ad58ab191652c7a144cd4203bb458f9a225f9 Mon Sep 17 00:00:00 2001
From: Anton Nikiforov <an.nikiforov@yadro.com>
Date: Tue, 19 Sep 2023 08:46:19 +0300
Subject: [PATCH] [#642] writecache: Remove usage of close channel in bbolt

Signed-off-by: Anton Nikiforov <an.nikiforov@yadro.com>
---
 .../writecache/writecachebbolt/cachebbolt.go  | 18 +++++------
 .../writecache/writecachebbolt/flush.go       | 32 +++++++------------
 2 files changed, 19 insertions(+), 31 deletions(-)

diff --git a/pkg/local_object_storage/writecache/writecachebbolt/cachebbolt.go b/pkg/local_object_storage/writecache/writecachebbolt/cachebbolt.go
index 363ee8448..9d54cd5c2 100644
--- a/pkg/local_object_storage/writecache/writecachebbolt/cachebbolt.go
+++ b/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()
diff --git a/pkg/local_object_storage/writecache/writecachebbolt/flush.go b/pkg/local_object_storage/writecache/writecachebbolt/flush.go
index fd322e9fa..393776dd1 100644
--- a/pkg/local_object_storage/writecache/writecachebbolt/flush.go
+++ b/pkg/local_object_storage/writecache/writecachebbolt/flush.go
@@ -36,20 +36,10 @@ const (
 )
 
 // runFlushLoop starts background workers which periodically flush objects to the blobstor.
-func (c *cache) runFlushLoop() {
-	ctx, cancel := context.WithCancel(context.Background())
-
-	ch := c.closeCh
-	c.wg.Add(1)
-	go func() {
-		<-ch
-		cancel()
-		c.wg.Done()
-	}()
-
+func (c *cache) runFlushLoop(ctx context.Context) {
 	for i := 0; i < c.workersCount; i++ {
 		c.wg.Add(1)
-		go c.workerFlushSmall()
+		go c.workerFlushSmall(ctx)
 	}
 
 	c.wg.Add(1)
@@ -68,20 +58,20 @@ func (c *cache) runFlushLoop() {
 		for {
 			select {
 			case <-tt.C:
-				c.flushSmallObjects()
+				c.flushSmallObjects(ctx)
 				tt.Reset(defaultFlushInterval)
-			case <-c.closeCh:
+			case <-ctx.Done():
 				return
 			}
 		}
 	}()
 }
 
-func (c *cache) flushSmallObjects() {
+func (c *cache) flushSmallObjects(ctx context.Context) {
 	var lastKey []byte
 	for {
 		select {
-		case <-c.closeCh:
+		case <-ctx.Done():
 			return
 		default:
 		}
@@ -137,7 +127,7 @@ func (c *cache) flushSmallObjects() {
 			count++
 			select {
 			case c.flushCh <- m[i]:
-			case <-c.closeCh:
+			case <-ctx.Done():
 				c.modeMtx.RUnlock()
 				return
 			}
@@ -170,7 +160,7 @@ func (c *cache) workerFlushBig(ctx context.Context) {
 			_ = c.flushFSTree(ctx, true)
 
 			c.modeMtx.RUnlock()
-		case <-c.closeCh:
+		case <-ctx.Done():
 			return
 		}
 	}
@@ -228,7 +218,7 @@ func (c *cache) flushFSTree(ctx context.Context, ignoreErrors bool) error {
 }
 
 // workerFlushSmall writes small objects to the main storage.
-func (c *cache) workerFlushSmall() {
+func (c *cache) workerFlushSmall(ctx context.Context) {
 	defer c.wg.Done()
 
 	var objInfo objectInfo
@@ -236,11 +226,11 @@ func (c *cache) workerFlushSmall() {
 		// Give priority to direct put.
 		select {
 		case objInfo = <-c.flushCh:
-		case <-c.closeCh:
+		case <-ctx.Done():
 			return
 		}
 
-		err := c.flushObject(context.TODO(), objInfo.obj, objInfo.data, writecache.StorageTypeDB)
+		err := c.flushObject(ctx, objInfo.obj, objInfo.data, writecache.StorageTypeDB)
 		if err != nil {
 			// Error is handled in flushObject.
 			continue