Reduce reactor stack trace depth (#9923)

instrumentation/reactor/reactor-3.1/library/src/main/java/io/opentelemetry/instrumentation/reactor/v3_1/TracingSubscriber.java

@@ -22,6 +22,7 @@ package io.opentelemetry.instrumentation.reactor.v3_1;
 
 import io.opentelemetry.api.trace.Span;
 import io.opentelemetry.context.Scope;
+import java.util.function.Supplier;
 import org.reactivestreams.Subscriber;
 import org.reactivestreams.Subscription;
 import reactor.core.CoreSubscriber;
@@ -56,30 +57,40 @@ public class TracingSubscriber<T> implements CoreSubscriber<T> {
 
   @Override
   public void onSubscribe(Subscription subscription) {
-    withActiveSpan(() -> subscriber.onSubscribe(subscription));
+    try (Scope ignore = openScope()) {
+      subscriber.onSubscribe(subscription);
+    }
   }
 
   @Override
   public void onNext(T o) {
-    withActiveSpan(() -> subscriber.onNext(o));
+    try (Scope ignore = openScope()) {
+      subscriber.onNext(o);
+    }
   }
 
   @Override
   public void onError(Throwable throwable) {
+    Supplier<Scope> scopeSupplier;
     if (!hasContextToPropagate
         && (fluxRetrySubscriberClass == subscriber.getClass()
             || fluxRetryWhenSubscriberClass == subscriber.getClass())) {
       // clear context for retry to avoid having retried operations run with currently active
       // context as parent context
-      withActiveSpan(io.opentelemetry.context.Context.root(), () -> subscriber.onError(throwable));
+      scopeSupplier = () -> openScope(io.opentelemetry.context.Context.root());
     } else {
-      withActiveSpan(() -> subscriber.onError(throwable));
+      scopeSupplier = () -> openScope();
+    }
+    try (Scope ignore = scopeSupplier.get()) {
+      subscriber.onError(throwable);
     }
   }
 
   @Override
   public void onComplete() {
-    withActiveSpan(subscriber::onComplete);
+    try (Scope ignore = openScope()) {
+      subscriber.onComplete();
+    }
   }
 
   @Override
@@ -87,18 +98,12 @@ public class TracingSubscriber<T> implements CoreSubscriber<T> {
     return context;
   }
 
-  private void withActiveSpan(Runnable runnable) {
-    withActiveSpan(hasContextToPropagate ? traceContext : null, runnable);
+  private Scope openScope() {
+    return openScope(hasContextToPropagate ? traceContext : null);
   }
 
-  private static void withActiveSpan(io.opentelemetry.context.Context context, Runnable runnable) {
-    if (context != null) {
-      try (Scope ignored = context.makeCurrent()) {
-        runnable.run();
-      }
-    } else {
-      runnable.run();
-    }
+  private static Scope openScope(io.opentelemetry.context.Context context) {
+    return context != null ? context.makeCurrent() : null;
   }
 
   private static Class<?> getFluxRetrySubscriberClass() {