avoid rwlock

Author: kwannoel

src/compute/src/rpc/service/exchange_service.rs

@@ -165,6 +165,10 @@ impl ExchangeServiceImpl {
         );
         pin_mut!(select_stream);
 
+        let exchange_frag_send_size_metrics = metrics
+                        .stream_fragment_exchange_bytes
+                        .with_label_values(&[&up_fragment_id, &down_fragment_id]);
+
         while let Some(r) = select_stream.try_next().await? {
             match r {
                 Either::Left(permits_to_add) => {
@@ -188,10 +192,7 @@ impl ExchangeServiceImpl {
 
                     yield response;
 
-                    metrics
-                        .stream_fragment_exchange_bytes
-                        .with_label_values(&[&up_fragment_id, &down_fragment_id])
-                        .inc_by(bytes as u64);
+                    exchange_frag_send_size_metrics.inc_by(bytes as u64);
                 }
             }
         }