fix

Author: sushanb

google-cloud-bigtable/src/main/java/com/google/cloud/bigtable/data/v2/internal/csm/tracers/BuiltinMetricsTracer.java

@@ -82,13 +82,12 @@ class BuiltinMetricsTracer extends BigtableTracer {
   private final AtomicLong totalClientBlockingTime = new AtomicLong(0);
 
   private final AtomicLong grpcMessageSentDelay = new AtomicLong(0);
-  private final AtomicLong grpcHeadersSentNanos = new AtomicLong(0);
-  private final AtomicLong grpcHeadersOutHeaderInLatency = new AtomicLong(0);
 
   private Deadline operationDeadline = null;
   private volatile Duration remainingDeadlineAtAttemptStart = Duration.ZERO;
 
   private volatile MetadataExtractorInterceptor.SidebandData sidebandData = new SidebandData();
+  private volatile Optional<Stopwatch> faket4t7 = Optional.empty();
 
   BuiltinMetricsTracer(
       MetricRegistry.RecorderRegistry recorder, ClientInfo clientInfo, MethodInfo methodInfo) {
@@ -267,14 +266,12 @@ public void grpcMessageSent() {
 
   @Override
   public void grpcHeadersSent() {
-    grpcHeadersSentNanos.set(attemptTimer.elapsed(TimeUnit.NANOSECONDS));
+    faket4t7 = Optional.of(Stopwatch.createStarted());
   }
 
   @Override
   public void grpcHeadersReceived() {
-    long receivedNanos = attemptTimer.elapsed(TimeUnit.NANOSECONDS);
-    long sentNanos = grpcHeadersSentNanos.get();
-    grpcHeadersOutHeaderInLatency.set(receivedNanos - sentNanos);
+    faket4t7.map(Stopwatch::stop);
   }
 
   @Override
@@ -411,17 +408,15 @@ private void recordAttemptCompletion(@Nullable Throwable throwable) {
           code,
           sidebandData.getGfeTiming());
     } else {
-      // Fallback to header latency if GFE timing is not available
-      long fallbackLatencyNanos = grpcHeadersOutHeaderInLatency.get();
-      if (fallbackLatencyNanos > 0) {
-        recorder.serverLatency.record(
-            clientInfo,
-            tableId,
-            methodInfo,
-            sidebandData.getClusterInfo(),
-            code,
-            Duration.ofNanos(fallbackLatencyNanos));
-      }
+      faket4t7.ifPresent(
+          stopwatch ->
+              recorder.serverLatency.record(
+                  clientInfo,
+                  tableId,
+                  methodInfo,
+                  sidebandData.getClusterInfo(),
+                  code,
+                  stopwatch.elapsed()));
     }
 
     boolean seenServer =