core: fix old ClientStreamTracer.Factory creating tracers twice (#8381)

Fix a bug introduced in #8355 : old ClientStreamTracer.Factory implementation creates tracers twice.

core/src/main/java/io/grpc/internal/GrpcUtil.java

@@ -65,7 +65,6 @@ import java.util.concurrent.Executors;
 import java.util.concurrent.ScheduledExecutorService;
 import java.util.concurrent.ThreadFactory;
 import java.util.concurrent.TimeUnit;
-import java.util.concurrent.atomic.AtomicReference;
 import java.util.logging.Level;
 import java.util.logging.Logger;
 import javax.annotation.Nullable;
@@ -785,15 +784,22 @@ public final class GrpcUtil {
     } else {
       streamTracer = new ForwardingClientStreamTracer() {
         final ClientStreamTracer noop = new ClientStreamTracer() {};
-        AtomicReference<ClientStreamTracer> delegate = new AtomicReference<>(noop);
+        volatile ClientStreamTracer delegate = noop;
 
         void maybeInit(StreamInfo info, Metadata headers) {
-          delegate.compareAndSet(noop, streamTracerFactory.newClientStreamTracer(info, headers));
+          if (delegate != noop) {
+            return;
+          }
+          synchronized (this) {
+            if (delegate == noop) {
+              delegate = streamTracerFactory.newClientStreamTracer(info, headers);
+            }
+          }
         }
 
         @Override
         protected ClientStreamTracer delegate() {
-          return delegate.get();
+          return delegate;
         }
 
         @SuppressWarnings("deprecation")

core/src/test/java/io/grpc/internal/GrpcUtilTest.java

@@ -38,6 +38,7 @@ import io.grpc.Status;
 import io.grpc.internal.ClientStreamListener.RpcProgress;
 import io.grpc.internal.GrpcUtil.Http2Error;
 import io.grpc.testing.TestMethodDescriptors;
+import java.util.ArrayDeque;
 import java.util.concurrent.atomic.AtomicReference;
 import org.junit.Rule;
 import org.junit.Test;
@@ -301,12 +302,14 @@ public class GrpcUtilTest {
     final AtomicReference<Attributes> transportAttrsRef = new AtomicReference<>();
     final ClientStreamTracer mockTracer = mock(ClientStreamTracer.class);
     final Metadata.Key<String> key = Metadata.Key.of("fake-key", Metadata.ASCII_STRING_MARSHALLER);
+    final ArrayDeque<ClientStreamTracer> tracers = new ArrayDeque<>();
     ClientStreamTracer.Factory oldFactoryImpl = new ClientStreamTracer.Factory() {
       @SuppressWarnings("deprecation")
       @Override
       public ClientStreamTracer newClientStreamTracer(StreamInfo info, Metadata headers) {
         transportAttrsRef.set(info.getTransportAttrs());
         headers.put(key, "fake-value");
+        tracers.offer(mockTracer);
         return mockTracer;
       }
     };
@@ -318,8 +321,12 @@ public class GrpcUtilTest {
         Attributes.newBuilder().set(Attributes.Key.<String>create("foo"), "bar").build();
     ClientStreamTracer tracer = GrpcUtil.newClientStreamTracer(oldFactoryImpl, info, metadata);
     tracer.streamCreated(transAttrs, metadata);
-
+    assertThat(tracers.poll()).isSameInstanceAs(mockTracer);
     assertThat(transportAttrsRef.get()).isEqualTo(transAttrs);
     assertThat(metadata.get(key)).isEqualTo("fake-value");
+
+    tracer.streamClosed(Status.UNAVAILABLE);
+    // verify that newClientStreamTracer() is called no more than once
+    assertThat(tracers).isEmpty();
   }
 }