Merge pull request #1246 from fededonna

* pr/1246:
  Polish "Expose prestartAllCoreThreads on ExecutorService"
  Expose prestartAllCoreThreads on ExecutorService

Closes gh-1246

spring-context/src/main/java/org/springframework/scheduling/concurrent/ThreadPoolExecutorFactoryBean.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2002-2018 the original author or authors.
+ * Copyright 2002-2021 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.
@@ -75,6 +75,8 @@ public class ThreadPoolExecutorFactoryBean extends ExecutorConfigurationSupport
 
 	private boolean allowCoreThreadTimeOut = false;
 
+	private boolean prestartAllCoreThreads = false;
+
 	private int queueCapacity = Integer.MAX_VALUE;
 
 	private boolean exposeUnconfigurableExecutor = false;
@@ -118,6 +120,16 @@ public void setAllowCoreThreadTimeOut(boolean allowCoreThreadTimeOut) {
 		this.allowCoreThreadTimeOut = allowCoreThreadTimeOut;
 	}
 
+	/**
+	 * Specify whether to start all core threads, causing them to idly wait for work.
+	 * <p>Default is "false".
+	 * @since 5.3.14
+	 * @see java.util.concurrent.ThreadPoolExecutor#prestartAllCoreThreads
+	 */
+	public void setPrestartAllCoreThreads(boolean prestartAllCoreThreads) {
+		this.prestartAllCoreThreads = prestartAllCoreThreads;
+	}
+
 	/**
 	 * Set the capacity for the ThreadPoolExecutor's BlockingQueue.
 	 * Default is {@code Integer.MAX_VALUE}.
@@ -153,6 +165,9 @@ protected ExecutorService initializeExecutor(
 		if (this.allowCoreThreadTimeOut) {
 			executor.allowCoreThreadTimeOut(true);
 		}
+		if (this.prestartAllCoreThreads) {
+			executor.prestartAllCoreThreads();
+		}
 
 		// Wrap executor with an unconfigurable decorator.
 		this.exposedExecutor = (this.exposeUnconfigurableExecutor ?

spring-context/src/main/java/org/springframework/scheduling/concurrent/ThreadPoolTaskExecutor.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2002-2020 the original author or authors.
+ * Copyright 2002-2021 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.
@@ -94,6 +94,8 @@ public class ThreadPoolTaskExecutor extends ExecutorConfigurationSupport
 
 	private boolean allowCoreThreadTimeOut = false;
 
+	private boolean prestartAllCoreThreads = false;
+
 	@Nullable
 	private TaskDecorator taskDecorator;
 
@@ -197,6 +199,16 @@ public void setAllowCoreThreadTimeOut(boolean allowCoreThreadTimeOut) {
 		this.allowCoreThreadTimeOut = allowCoreThreadTimeOut;
 	}
 
+	/**
+	 * Specify whether to start all core threads, causing them to idly wait for work.
+	 * <p>Default is "false".
+	 * @since 5.3.14
+	 * @see java.util.concurrent.ThreadPoolExecutor#prestartAllCoreThreads
+	 */
+	public void setPrestartAllCoreThreads(boolean prestartAllCoreThreads) {
+		this.prestartAllCoreThreads = prestartAllCoreThreads;
+	}
+
 	/**
 	 * Specify a custom {@link TaskDecorator} to be applied to any {@link Runnable}
 	 * about to be executed.
@@ -256,6 +268,9 @@ public void execute(Runnable command) {
 		if (this.allowCoreThreadTimeOut) {
 			executor.allowCoreThreadTimeOut(true);
 		}
+		if (this.prestartAllCoreThreads) {
+			executor.prestartAllCoreThreads();
+		}
 
 		this.threadPoolExecutor = executor;
 		return executor;

spring-context/src/test/java/org/springframework/scheduling/concurrent/ThreadPoolExecutorFactoryBeanTests.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2002-2020 the original author or authors.
+ * Copyright 2002-2021 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.
@@ -16,19 +16,29 @@
 
 package org.springframework.scheduling.concurrent;
 
+import java.util.concurrent.BlockingQueue;
 import java.util.concurrent.ExecutorService;
 import java.util.concurrent.FutureTask;
+import java.util.concurrent.RejectedExecutionHandler;
+import java.util.concurrent.ThreadFactory;
+import java.util.concurrent.ThreadPoolExecutor;
 
 import org.junit.jupiter.api.Test;
 
 import org.springframework.context.ConfigurableApplicationContext;
 import org.springframework.context.annotation.AnnotationConfigApplicationContext;
 import org.springframework.context.annotation.Bean;
 import org.springframework.context.annotation.Configuration;
+import org.springframework.context.support.GenericApplicationContext;
 
 import static org.assertj.core.api.Assertions.assertThat;
+import static org.mockito.Mockito.mock;
+import static org.mockito.Mockito.never;
+import static org.mockito.Mockito.verify;
 
 /**
+ * Tests for {@link ThreadPoolExecutorFactoryBean}.
+ *
  * @author Juergen Hoeller
  */
 class ThreadPoolExecutorFactoryBeanTests {
@@ -44,6 +54,27 @@ void defaultExecutor() throws Exception {
 		context.close();
 	}
 
+	@Test
+	void executorWithDefaultSettingsDoesNotPrestartAllCoreThreads() {
+		GenericApplicationContext context = new GenericApplicationContext();
+		context.registerBean("taskExecutor", ThreadPoolExecutorFactoryBean.class, TestThreadPoolExecutorFactoryBean::new);
+		context.refresh();
+		ThreadPoolExecutor threadPoolExecutor = context.getBean(ThreadPoolExecutor.class);
+		verify(threadPoolExecutor, never()).prestartAllCoreThreads();
+	}
+
+	@Test
+	void executorWithPrestartAllCoreThreads() {
+		GenericApplicationContext context = new GenericApplicationContext();
+		context.registerBean("taskExecutor", ThreadPoolExecutorFactoryBean.class, () -> {
+			TestThreadPoolExecutorFactoryBean factoryBean = new TestThreadPoolExecutorFactoryBean();
+			factoryBean.setPrestartAllCoreThreads(true);
+			return factoryBean;
+		});
+		context.refresh();
+		ThreadPoolExecutor threadPoolExecutor = context.getBean(ThreadPoolExecutor.class);
+		verify(threadPoolExecutor).prestartAllCoreThreads();
+	}
 
 	@Configuration
 	static class ExecutorConfig {
@@ -55,4 +86,15 @@ ThreadPoolExecutorFactoryBean executor() {
 
 	}
 
+	private static class TestThreadPoolExecutorFactoryBean extends ThreadPoolExecutorFactoryBean {
+
+		@Override
+		protected ThreadPoolExecutor createExecutor(
+				int corePoolSize, int maxPoolSize, int keepAliveSeconds, BlockingQueue<Runnable> queue,
+				ThreadFactory threadFactory, RejectedExecutionHandler rejectedExecutionHandler) {
+
+			return mock(ThreadPoolExecutor.class);
+		}
+	}
+
 }