Split up BackgroundPreinitializer

Issue: 44065

spring-boot-project/spring-boot-autoconfigure/src/main/java/org/springframework/boot/autoconfigure/preinitialize/BackgroundPreinitializer.java

@@ -0,0 +1,35 @@
+/*
+ * Copyright 2012-2024 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.autoconfigure.preinitialize;
+
+/**
+ * Interface used to preinitialize in the background code that may otherwise cause a delay
+ * when first called. Implementations should be registered in {@code spring.factories}.
+ *
+ * @author Phillip Webb
+ * @since 4.0.0
+ */
+@FunctionalInterface
+public interface BackgroundPreinitializer {
+
+	/**
+	 * Perform any require preinitialization.
+	 * @throws Exception on any initialization error
+	 */
+	void preinitialize() throws Exception;
+
+}

spring-boot-project/spring-boot-autoconfigure/src/main/java/org/springframework/boot/autoconfigure/preinitialize/BackgroundPreinitializingApplicationListener.java

@@ -0,0 +1,133 @@
+/*
+ * Copyright 2012-2025 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.autoconfigure.preinitialize;
+
+import java.util.List;
+import java.util.concurrent.CountDownLatch;
+import java.util.concurrent.atomic.AtomicBoolean;
+
+import org.springframework.boot.context.event.ApplicationEnvironmentPreparedEvent;
+import org.springframework.boot.context.event.ApplicationFailedEvent;
+import org.springframework.boot.context.event.ApplicationReadyEvent;
+import org.springframework.boot.context.event.SpringApplicationEvent;
+import org.springframework.boot.context.logging.LoggingApplicationListener;
+import org.springframework.context.ApplicationListener;
+import org.springframework.core.NativeDetector;
+import org.springframework.core.Ordered;
+import org.springframework.core.io.support.SpringFactoriesLoader;
+
+/**
+ * {@link ApplicationListener} to trigger early initialization in a background thread of
+ * time-consuming tasks.
+ * <p>
+ * Set the {@link #IGNORE_BACKGROUNDPREINITIALIZER_PROPERTY_NAME} system property to
+ * {@code true} to disable this mechanism.
+ *
+ * @author Phillip Webb
+ * @author Andy Wilkinson
+ * @author Artsiom Yudovin
+ * @author Sebastien Deleuze
+ * @see BackgroundPreinitializer
+ */
+class BackgroundPreinitializingApplicationListener implements ApplicationListener<SpringApplicationEvent>, Ordered {
+
+	/**
+	 * System property that instructs Spring Boot how to run pre initialization. When the
+	 * property is set to {@code true}, no pre-initialization happens and each item is
+	 * initialized in the foreground as it needs to. When the property is {@code false}
+	 * (default), pre initialization runs in a separate thread in the background.
+	 */
+	public static final String IGNORE_BACKGROUNDPREINITIALIZER_PROPERTY_NAME = "spring.backgroundpreinitializer.ignore";
+
+	private static final AtomicBoolean started = new AtomicBoolean();
+
+	private static final CountDownLatch complete = new CountDownLatch(1);
+
+	private final SpringFactoriesLoader factoriesLoader;
+
+	private final boolean enabled;
+
+	BackgroundPreinitializingApplicationListener() {
+		this(SpringFactoriesLoader.forDefaultResourceLocation());
+	}
+
+	BackgroundPreinitializingApplicationListener(SpringFactoriesLoader factoriesLoader) {
+		this.factoriesLoader = factoriesLoader;
+		this.enabled = !NativeDetector.inNativeImage()
+				&& !Boolean.getBoolean(IGNORE_BACKGROUNDPREINITIALIZER_PROPERTY_NAME)
+				&& Runtime.getRuntime().availableProcessors() > 1;
+	}
+
+	@Override
+	public int getOrder() {
+		return LoggingApplicationListener.DEFAULT_ORDER + 1;
+	}
+
+	@Override
+	public void onApplicationEvent(SpringApplicationEvent event) {
+		if (!this.enabled) {
+			return;
+		}
+		if (event instanceof ApplicationEnvironmentPreparedEvent && started.compareAndSet(false, true)) {
+			preinitialize();
+		}
+		if ((event instanceof ApplicationReadyEvent || event instanceof ApplicationFailedEvent) && started.get()) {
+			try {
+				complete.await();
+			}
+			catch (InterruptedException ex) {
+				Thread.currentThread().interrupt();
+			}
+		}
+	}
+
+	private void preinitialize() {
+		Runner runner = new Runner(this.factoriesLoader.load(BackgroundPreinitializer.class));
+		try {
+			Thread thread = new Thread(runner, "background-preinit");
+			thread.start();
+		}
+		catch (Exception ex) {
+			// This will fail on Google App Engine where creating threads is
+			// prohibited. We can safely continue but startup will be slightly slower
+			// as the initialization will now happen on the main thread.
+			complete.countDown();
+		}
+	}
+
+	/**
+	 * Runner thread to call the {@link BackgroundPreinitializer} instances.
+	 *
+	 * @param preinitializers the preinitializers
+	 */
+	record Runner(List<BackgroundPreinitializer> preinitializers) implements Runnable {
+
+		@Override
+		public void run() {
+			for (BackgroundPreinitializer preinitializer : this.preinitializers) {
+				try {
+					preinitializer.preinitialize();
+				}
+				catch (Throwable ex) {
+				}
+			}
+			complete.countDown();
+		}
+
+	}
+
+}