Ensures that sampler proxy gets eagerly resolved; fixes gh-2107

spring-cloud-sleuth-autoconfigure/src/main/java/org/springframework/cloud/sleuth/autoconfig/instrument/redis/TraceRedisAutoConfiguration.java

@@ -16,6 +16,7 @@
 
 package org.springframework.cloud.sleuth.autoconfig.instrument.redis;
 
+import brave.sampler.Sampler;
 import io.lettuce.core.tracing.Tracing;
 
 import org.springframework.boot.autoconfigure.AutoConfigureBefore;
@@ -51,10 +52,22 @@ public class TraceRedisAutoConfiguration {
 
 		@Bean
 		@ConditionalOnBean(Tracing.class)
-		TraceLettuceClientResourcesBuilderCustomizer traceLettuceClientResourcesBuilderCustomizer(Tracing tracing) {
+		TraceLettuceClientResourcesBuilderCustomizer traceLettuceClientResourcesBuilderCustomizer(Tracing tracing,
+				Sampler sampler) {
+			eagerlyInitializePotentiallyRefreshScopeSampler(sampler);
 			return new TraceLettuceClientResourcesBuilderCustomizer(tracing);
 		}
 
+		/**
+		 * We need to do the eager method invocation. Since this might be @RefreshScope, a
+		 * proxy is being created. Trying to resolve the proxy from a different thread
+		 * than main can lead to cross thread locking.
+		 * @param sampler potentially refresh scope sampler
+		 */
+		private void eagerlyInitializePotentiallyRefreshScopeSampler(Sampler sampler) {
+			sampler.isSampled(0L);
+		}
+
 	}
 
 }

spring-cloud-sleuth-instrumentation/src/test/java/org/springframework/cloud/sleuth/instrument/messaging/TraceFunctionAroundWrapperTests.java

@@ -151,6 +151,19 @@ class TraceFunctionAroundWrapperTests {
 		assertThat(tracer.spans).isEmpty();
 	}
 
+	@Test
+	void test_tracing_with_message_flux_to_flux_without_message() {
+		FunctionRegistration<MessageFluxToFluxFunction> registration = new FunctionRegistration<>(
+				new MessageFluxToFluxFunction(), "greeter").type(FunctionType.of(MessageFluxToFluxFunction.class));
+		catalog.register(registration);
+		FunctionInvocationWrapper function = catalog.lookup("greeter");
+
+		Object result = (Object) ((Flux) wrapper.apply("hello", function)).blockFirst();
+
+		assertThat(result).isEqualTo("hello");
+		assertThat(tracer.spans).isEmpty();
+	}
+
 	@Test
 	void test_tracing_with_consumer() {
 		GreeterConsumer consumer = new GreeterConsumer();
@@ -465,4 +478,18 @@ class TraceFunctionAroundWrapperTests {
 
 	}
 
+	static class MessageFluxToFluxFunction implements Function<Flux<Message<?>>, Flux<?>> {
+
+		private static final Logger log = LoggerFactory.getLogger(MessageFluxToFluxFunction.class);
+
+		@Override
+		public Flux<?> apply(Flux<Message<?>> input) {
+			return input.map(s -> {
+				log.info("Logging [{}] from map", s);
+				return s.getPayload();
+			});
+		}
+
+	}
+
 }