diff --git a/pkg/depth/buffer.go b/pkg/depth/buffer.go
index 0b627f255..c960dfb2f 100644
--- a/pkg/depth/buffer.go
+++ b/pkg/depth/buffer.go
@@ -92,10 +92,6 @@ func (b *Buffer) AddUpdate(o types.SliceOrderBook, firstUpdateID int64, finalArg
 		Object:        o,
 	}
 
-	// we lock here because there might be 2+ calls to the AddUpdate method
-	// we don't want to reset sync.Once 2 times here
-	b.mu.Lock()
-	defer b.mu.Unlock()
 	select {
 	case <-b.resetC:
 		log.Warnf("received depth reset signal, resetting...")
@@ -106,11 +102,13 @@ func (b *Buffer) AddUpdate(o types.SliceOrderBook, firstUpdateID int64, finalArg
 	}
 
 	// if the snapshot is set to nil, we need to buffer the message
+	b.mu.Lock()
 	if b.snapshot == nil {
 		b.buffer = append(b.buffer, u)
 		b.once.Do(func() {
 			go b.tryFetch()
 		})
+		b.mu.Unlock()
 		return nil
 	}
 
@@ -121,6 +119,7 @@ func (b *Buffer) AddUpdate(o types.SliceOrderBook, firstUpdateID int64, finalArg
 		finalUpdateID = b.finalUpdateID
 		b.resetSnapshot()
 		b.emitReset()
+		b.mu.Unlock()
 		return fmt.Errorf("found missing update between finalUpdateID %d and firstUpdateID %d, diff: %d",
 			finalUpdateID+1,
 			u.FirstUpdateID,
@@ -129,18 +128,19 @@ func (b *Buffer) AddUpdate(o types.SliceOrderBook, firstUpdateID int64, finalArg
 
 	log.Debugf("depth update id %d -> %d", b.finalUpdateID, u.FinalUpdateID)
 	b.finalUpdateID = u.FinalUpdateID
+	b.mu.Unlock()
+
 	b.EmitPush(u)
 	return nil
 }
 
 func (b *Buffer) fetchAndPush() error {
-	b.mu.Lock()
-	defer b.mu.Unlock()
 	book, finalUpdateID, err := b.fetcher()
 	if err != nil {
 		return err
 	}
 
+	b.mu.Lock()
 	log.Debugf("fetched depth snapshot, final update id %d", finalUpdateID)
 
 	if len(b.buffer) > 0 {
@@ -148,6 +148,7 @@ func (b *Buffer) fetchAndPush() error {
 		if finalUpdateID < b.buffer[0].FirstUpdateID {
 			b.resetSnapshot()
 			b.emitReset()
+			b.mu.Unlock()
 			return fmt.Errorf("depth snapshot is too early, final update %d is < the first update id %d", finalUpdateID, b.buffer[0].FirstUpdateID)
 		}
 	}
@@ -162,6 +163,7 @@ func (b *Buffer) fetchAndPush() error {
 		if u.FirstUpdateID > finalUpdateID+1 {
 			b.resetSnapshot()
 			b.emitReset()
+			b.mu.Unlock()
 			return fmt.Errorf("there is a missing depth update, the update id %d > final update id %d + 1", u.FirstUpdateID, finalUpdateID)
 		}
 
@@ -180,6 +182,9 @@ func (b *Buffer) fetchAndPush() error {
 	// set the snapshot
 	b.snapshot = &book
 
+	b.mu.Unlock()
+
+	// should unlock first then call ready
 	b.EmitReady(book, pushUpdates)
 	return nil
 }
diff --git a/pkg/depth/buffer_test.go b/pkg/depth/buffer_test.go
index 9c33effdd..949db0f21 100644
--- a/pkg/depth/buffer_test.go
+++ b/pkg/depth/buffer_test.go
@@ -1,3 +1,6 @@
+//go:build !race
+// +build !race
+
 package depth
 
 import (
@@ -5,9 +8,10 @@ import (
 	"testing"
 	"time"
 
+	"github.com/stretchr/testify/assert"
+
 	"github.com/c9s/bbgo/pkg/fixedpoint"
 	"github.com/c9s/bbgo/pkg/types"
-	"github.com/stretchr/testify/assert"
 )
 
 var itov = fixedpoint.NewFromInt