kvserver: use type-safe atomics in raftSendQueue

Go 1.19 introduced atomic types that enforce atomic access to variables, which
in many situation is less error-prone. This commit resolves a TODO to take
advantage of these types.

Release note: None

pkg/kv/kvserver/raft_transport.go

@@ -166,8 +166,7 @@ type raftSendQueue struct {
 	reqs chan *kvserverpb.RaftMessageRequest
 	// The number of bytes in flight. Must be updated *atomically* on sending and
 	// receiving from the reqs channel.
-	// TODO(pavelkalinnikov): replace by atomic.Int64 when CRDB uses Go 1.19.
-	bytes int64
+	bytes atomic.Int64
 }
 
 // NewDummyRaftTransport returns a dummy raft transport for use in tests which
@@ -228,7 +227,7 @@ func (t *RaftTransport) queueMessageCount() int64 {
 // queueByteSize returns the total bytes size of outgoing messages in the queue.
 func (t *RaftTransport) queueByteSize() int64 {
 	var size int64
-	t.visitQueues(func(q *raftSendQueue) { size += atomic.LoadInt64(&q.bytes) })
+	t.visitQueues(func(q *raftSendQueue) { size += q.bytes.Load() })
 	return size
 }
 
@@ -441,7 +440,7 @@ func (t *RaftTransport) processQueue(
 			return err
 		case req := <-q.reqs:
 			size := int64(req.Size())
-			atomic.AddInt64(&q.bytes, -size)
+			q.bytes.Add(-size)
 			budget := targetRaftOutgoingBatchSize.Get(&t.st.SV) - size
 			batch.Requests = append(batch.Requests, *req)
 			releaseRaftMessageRequest(req)
@@ -450,7 +449,7 @@ func (t *RaftTransport) processQueue(
 				select {
 				case req = <-q.reqs:
 					size := int64(req.Size())
-					atomic.AddInt64(&q.bytes, -size)
+					q.bytes.Add(-size)
 					budget -= size
 					batch.Requests = append(batch.Requests, *req)
 					releaseRaftMessageRequest(req)
@@ -532,7 +531,7 @@ func (t *RaftTransport) SendAsync(
 	size := int64(req.Size())
 	select {
 	case q.reqs <- req:
-		atomic.AddInt64(&q.bytes, size)
+		q.bytes.Add(size)
 		return true
 	default:
 		if logRaftSendQueueFullEvery.ShouldLog() {
@@ -564,7 +563,7 @@ func (t *RaftTransport) startProcessNewQueue(
 		for {
 			select {
 			case req := <-q.reqs:
-				atomic.AddInt64(&q.bytes, -int64(req.Size()))
+				q.bytes.Add(-int64(req.Size()))
 				t.metrics.MessagesDropped.Inc(1)
 				releaseRaftMessageRequest(req)
 			default: