From e29853fcc71c73e2b6b2897f42f72611448ab677 Mon Sep 17 00:00:00 2001
From: Oliver Drotbohm <oliver.drotbohm@broadcom.com>
Date: Tue, 21 May 2024 00:57:08 +0200
Subject: [PATCH] GH-587 - Avoid repeated lookup of ApplicationModules in
 ApplicationModulesRuntime.

---
 .../runtime/ApplicationModulesRuntime.java    |  3 +-
 ...icationModulesRuntimeIntegrationTests.java | 34 +++++++++++++++++++
 2 files changed, 36 insertions(+), 1 deletion(-)

diff --git a/spring-modulith-runtime/src/main/java/org/springframework/modulith/runtime/ApplicationModulesRuntime.java b/spring-modulith-runtime/src/main/java/org/springframework/modulith/runtime/ApplicationModulesRuntime.java
index 629f158a..5aea0a0c 100644
--- a/spring-modulith-runtime/src/main/java/org/springframework/modulith/runtime/ApplicationModulesRuntime.java
+++ b/spring-modulith-runtime/src/main/java/org/springframework/modulith/runtime/ApplicationModulesRuntime.java
@@ -19,6 +19,7 @@ import java.util.function.Supplier;
 
 import org.springframework.modulith.core.ApplicationModules;
 import org.springframework.util.Assert;
+import org.springframework.util.function.SingletonSupplier;
 
 /**
  * Bootstrap type to make sure we only bootstrap the initialization of a {@link ApplicationModules} instance once per
@@ -43,7 +44,7 @@ public class ApplicationModulesRuntime implements Supplier<ApplicationModules> {
 		Assert.notNull(modules, "ApplicationModules must not be null!");
 		Assert.notNull(runtime, "ApplicationRuntime must not be null!");
 
-		this.modules = modules;
+		this.modules = SingletonSupplier.of(modules);
 		this.runtime = runtime;
 	}
 
diff --git a/spring-modulith-runtime/src/test/java/org/springframework/modulith/runtime/ApplicationModulesRuntimeIntegrationTests.java b/spring-modulith-runtime/src/test/java/org/springframework/modulith/runtime/ApplicationModulesRuntimeIntegrationTests.java
index c615c4c3..fb77e0b4 100644
--- a/spring-modulith-runtime/src/test/java/org/springframework/modulith/runtime/ApplicationModulesRuntimeIntegrationTests.java
+++ b/spring-modulith-runtime/src/test/java/org/springframework/modulith/runtime/ApplicationModulesRuntimeIntegrationTests.java
@@ -21,6 +21,7 @@ import different.moduleB.ModuleBType;
 import example.SampleApplication;
 import example.moduleA.ModuleAType;
 
+import java.util.function.Supplier;
 import java.util.stream.Stream;
 
 import org.junit.jupiter.api.Test;
@@ -49,4 +50,37 @@ public class ApplicationModulesRuntimeIntegrationTests {
 		Stream.of(ModuleAType.class, ModuleBType.class)
 				.forEach(it -> assertThat(runtime.isApplicationClass(it)).isTrue());
 	}
+
+	@Test // GH-587
+	void onlyLooksUpApplicationModulesOnce() {
+
+		var context = SpringApplication.run(SampleApplication.class);
+		var applicationRuntime = new TestSpringBootApplicationRuntime(context);
+		var supplier = new CountingSupplier<>(() -> modules);
+
+		var runtime = new ApplicationModulesRuntime(supplier, applicationRuntime);
+
+		runtime.get();
+		runtime.get();
+
+		assertThat(supplier.counter).isEqualTo(1);
+	}
+
+	static class CountingSupplier<T> implements Supplier<T> {
+
+		private final Supplier<T> delegate;
+		private int counter = 0;
+
+		CountingSupplier(Supplier<T> delegate) {
+			this.delegate = delegate;
+		}
+
+		@Override
+		public T get() {
+
+			counter++;
+
+			return delegate.get();
+		}
+	}
 }