Remove spring.event.invoke-listener startup event

Prior to this commit, the `SimpleApplicationEventMulticaster` would be
instrumented with the `ApplicationStartup` and start/stop events for
invoking event listeners (`spring.event.invoke-listener`).

This feature was already limited to single-threaded event publishers,
but is still flawed since several types of events can happen
concurrently. Due to the single-threaded nature of the startup sequence,
our implementation should not produce startup events concurrently.

This can cause issues like gh-26057, where concurrent events lead to
inconcistencies when tracking parent/child relationships.

This commit removes the `spring.event.invoke-listener` startup event as
a result.

Fixes gh-26057

Author: bclozel

spring-context/src/main/java/org/springframework/context/event/SimpleApplicationEventMulticaster.java

@@ -25,8 +25,6 @@
 import org.springframework.context.ApplicationEvent;
 import org.springframework.context.ApplicationListener;
 import org.springframework.core.ResolvableType;
-import org.springframework.core.metrics.ApplicationStartup;
-import org.springframework.core.metrics.StartupStep;
 import org.springframework.lang.Nullable;
 import org.springframework.util.ErrorHandler;
 
@@ -57,9 +55,6 @@ public class SimpleApplicationEventMulticaster extends AbstractApplicationEventM
 	@Nullable
 	private ErrorHandler errorHandler;
 
-	@Nullable
-	private ApplicationStartup applicationStartup;
-
 
 	/**
 	 * Create a new SimpleApplicationEventMulticaster.
@@ -127,22 +122,6 @@ protected ErrorHandler getErrorHandler() {
 		return this.errorHandler;
 	}
 
-	/**
-	 * Set the {@link ApplicationStartup} to track event listener invocations during startup.
-	 * @since 5.3
-	 */
-	public void setApplicationStartup(@Nullable ApplicationStartup applicationStartup) {
-		this.applicationStartup = applicationStartup;
-	}
-
-	/**
-	 * Return the current application startup for this multicaster.
-	 */
-	@Nullable
-	public ApplicationStartup getApplicationStartup() {
-		return this.applicationStartup;
-	}
-
 	@Override
 	public void multicastEvent(ApplicationEvent event) {
 		multicastEvent(event, resolveDefaultEventType(event));
@@ -156,16 +135,6 @@ public void multicastEvent(final ApplicationEvent event, @Nullable ResolvableTyp
 			if (executor != null) {
 				executor.execute(() -> invokeListener(listener, event));
 			}
-			else if (this.applicationStartup != null) {
-				StartupStep invocationStep = this.applicationStartup.start("spring.event.invoke-listener");
-				invokeListener(listener, event);
-				invocationStep.tag("event", event::toString);
-				if (eventType != null) {
-					invocationStep.tag("eventType", eventType::toString);
-				}
-				invocationStep.tag("listener", listener::toString);
-				invocationStep.end();
-			}
 			else {
 				invokeListener(listener, event);
 			}

spring-context/src/main/java/org/springframework/context/support/AbstractApplicationContext.java

@@ -815,9 +815,7 @@ protected void initApplicationEventMulticaster() {
 			}
 		}
 		else {
-			SimpleApplicationEventMulticaster simpleApplicationEventMulticaster = new SimpleApplicationEventMulticaster(beanFactory);
-			simpleApplicationEventMulticaster.setApplicationStartup(getApplicationStartup());
-			this.applicationEventMulticaster = simpleApplicationEventMulticaster;
+			this.applicationEventMulticaster = new SimpleApplicationEventMulticaster(beanFactory);
 			beanFactory.registerSingleton(APPLICATION_EVENT_MULTICASTER_BEAN_NAME, this.applicationEventMulticaster);
 			if (logger.isTraceEnabled()) {
 				logger.trace("No '" + APPLICATION_EVENT_MULTICASTER_BEAN_NAME + "' bean, using " +

src/docs/asciidoc/core/core-appendix.adoc

@@ -1669,8 +1669,4 @@ its behavior changes.
 | `spring.context.refresh`
 | Application context refresh phase.
 |
-
-| `spring.event.invoke-listener`
-| Invocation of event listeners, if done in the main thread.
-| `event` the current application event, `eventType` its type and `listener` the listener processing this event.
 |===