Fix parallel startup of testcontainers

Update `TestcontainersLifecycleBeanPostProcessor` so that containers
can actually be started in parallel.

Prior to this commit, `initializeStartables` would collect beans
and in the process trigger the `postProcessAfterInitialization` method
on each bean. This would see that  `startablesInitialized` was `true`
and call `startableBean.start` directly. The result of this was that
beans were actually started sequentially and when the `start` method
was finally called it had nothing to do.

The updated code uses an enum rather than a boolean so that the
`postProcessAfterInitialization` method no longer attempts to start
beans unless `initializeStartables` has finished.

Fixes gh-38831

spring-boot-project/spring-boot-testcontainers/src/main/java/org/springframework/boot/testcontainers/lifecycle/TestcontainersLifecycleBeanPostProcessor.java

@@ -21,6 +21,7 @@
 import java.util.List;
 import java.util.Set;
 import java.util.concurrent.atomic.AtomicBoolean;
+import java.util.concurrent.atomic.AtomicReference;
 import java.util.stream.Collectors;
 
 import org.apache.commons.logging.Log;
@@ -63,7 +64,7 @@ class TestcontainersLifecycleBeanPostProcessor implements DestructionAwareBeanPo
 
 	private final TestcontainersStartup startup;
 
-	private final AtomicBoolean startablesInitialized = new AtomicBoolean();
+	private final AtomicReference<Startables> startables = new AtomicReference<>(Startables.UNSTARTED);
 
 	private final AtomicBoolean containersInitialized = new AtomicBoolean();
 
@@ -79,28 +80,33 @@ public Object postProcessAfterInitialization(Object bean, String beanName) throw
 			initializeContainers();
 		}
 		if (bean instanceof Startable startableBean) {
-			if (this.startablesInitialized.compareAndSet(false, true)) {
+			if (this.startables.compareAndExchange(Startables.UNSTARTED, Startables.STARTING) == Startables.UNSTARTED) {
 				initializeStartables(startableBean, beanName);
 			}
-			else {
+			else if (this.startables.get() == Startables.STARTED) {
+				logger.trace(LogMessage.format("Starting container %s", beanName));
 				startableBean.start();
 			}
 		}
 		return bean;
 	}
 
 	private void initializeStartables(Startable startableBean, String startableBeanName) {
+		logger.trace(LogMessage.format("Initializing startables"));
 		List<String> beanNames = new ArrayList<>(
 				List.of(this.beanFactory.getBeanNamesForType(Startable.class, false, false)));
 		beanNames.remove(startableBeanName);
 		List<Object> beans = getBeans(beanNames);
 		if (beans == null) {
-			this.startablesInitialized.set(false);
+			logger.trace(LogMessage.format("Failed to obtain startables %s", beanNames));
+			this.startables.set(Startables.UNSTARTED);
 			return;
 		}
 		beanNames.add(startableBeanName);
 		beans.add(startableBean);
+		logger.trace(LogMessage.format("Starting startables %s", beanNames));
 		start(beans);
+		this.startables.set(Startables.STARTED);
 		if (!beanNames.isEmpty()) {
 			logger.debug(LogMessage.format("Initialized and started startable beans '%s'", beanNames));
 		}
@@ -115,8 +121,14 @@ private void start(List<Object> beans) {
 	}
 
 	private void initializeContainers() {
+		logger.trace("Initializing containers");
 		List<String> beanNames = List.of(this.beanFactory.getBeanNamesForType(ContainerState.class, false, false));
-		if (getBeans(beanNames) == null) {
+		List<Object> beans = getBeans(beanNames);
+		if (beans != null) {
+			logger.trace(LogMessage.format("Initialized containers %s", beanNames));
+		}
+		else {
+			logger.trace(LogMessage.format("Failed to initialize containers %s", beanNames));
 			this.containersInitialized.set(false);
 		}
 	}
@@ -164,4 +176,10 @@ private boolean isReusedContainer(Object bean) {
 		return (bean instanceof GenericContainer<?> container) && container.isShouldBeReused();
 	}
 
+	enum Startables {
+
+		UNSTARTED, STARTING, STARTED
+
+	}
+
 }

spring-boot-project/spring-boot-testcontainers/src/test/java/org/springframework/boot/testcontainers/lifecycle/TestContainersParallelStartupIntegrationTests.java

@@ -0,0 +1,75 @@
+/*
+ * Copyright 2012-2023 the original author or authors.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      https://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package org.springframework.boot.testcontainers.lifecycle;
+
+import org.junit.jupiter.api.Test;
+import org.junit.jupiter.api.extension.ExtendWith;
+import org.testcontainers.containers.PostgreSQLContainer;
+
+import org.springframework.boot.test.system.CapturedOutput;
+import org.springframework.boot.test.system.OutputCaptureExtension;
+import org.springframework.boot.testcontainers.lifecycle.TestContainersParallelStartupIntegrationTests.ContainerConfig;
+import org.springframework.boot.testsupport.testcontainers.DisabledIfDockerUnavailable;
+import org.springframework.boot.testsupport.testcontainers.DockerImageNames;
+import org.springframework.context.annotation.Bean;
+import org.springframework.context.annotation.Configuration;
+import org.springframework.test.annotation.DirtiesContext;
+import org.springframework.test.context.ContextConfiguration;
+import org.springframework.test.context.TestPropertySource;
+import org.springframework.test.context.junit.jupiter.SpringExtension;
+
+import static org.assertj.core.api.Assertions.assertThat;
+
+/**
+ * Integration test for parallel startup.
+ *
+ * @author Phillip Webb
+ */
+@ExtendWith(SpringExtension.class)
+@ContextConfiguration(classes = ContainerConfig.class)
+@TestPropertySource(properties = "spring.testcontainers.beans.startup=parallel")
+@DirtiesContext
+@DisabledIfDockerUnavailable
+@ExtendWith(OutputCaptureExtension.class)
+public class TestContainersParallelStartupIntegrationTests {
+
+	@Test
+	void startsInParallel(CapturedOutput out) {
+		assertThat(out).contains("-lifecycle-0").contains("-lifecycle-1").contains("-lifecycle-2");
+	}
+
+	@Configuration(proxyBeanMethods = false)
+	static class ContainerConfig {
+
+		@Bean
+		static PostgreSQLContainer<?> container1() {
+			return new PostgreSQLContainer<>(DockerImageNames.postgresql());
+		}
+
+		@Bean
+		static PostgreSQLContainer<?> container2() {
+			return new PostgreSQLContainer<>(DockerImageNames.postgresql());
+		}
+
+		@Bean
+		static PostgreSQLContainer<?> container3() {
+			return new PostgreSQLContainer<>(DockerImageNames.postgresql());
+		}
+
+	}
+
+}