背景最近项目在jenkins部署的时候发现部署很慢，查看部署日志发现kill命令执行后应用pid还存在，导致必须在60秒等待期后kill -9杀死springboot进程

应用环境

• springboot

<dependency>
  <groupId>org.springframework.boot</groupId>
  <artifactId>spring-boot-starter</artifactId>
  <version>2.6.3</version>
</dependency>

• springcloud

<dependency>
    <groupId>com.alibaba.cloud</groupId>
    <artifactId>spring-cloud-alibaba-dependencies</artifactId>
    <version>2021.0.1.0</version>
    <type>pom</type>
    <scope>import</scope>
</dependency>

• 监控

<dependency>
  <groupId>org.springframework.boot</groupId>
  <artifactId>spring-boot-starter-actuator</artifactId>
  <version>2.6.3</version>
</dependency>

原因分析

• 通过将全部日志调整为debug级别，观察到有个定时任务线程在不断执行，例子如下

@SpringBootApplication
@MapperScan("com.test.test.mapper")
public class TestApplication implements CommandLineRunner {

	static ScheduledExecutorService executor;

	public static void main(String[] args) {
		executor = Executors.newScheduledThreadPool(1);
		SpringApplication.run(TestApplication.class, args);
	}

	private static void run(ScheduledExecutorService executor) {
		executor.scheduleAtFixedRate(() -> {
			System.out.println("run");
		}, 0, 1, TimeUnit.SECONDS);

	@Override
	public void run(String... args) throws Exception {
		run(executor);
	}
}

上述代码中，由于线程定义默认是非守护线程，执行优雅停机后，在用户线程停止后，非守护线程不会自动停止

解决办法

1. 定义为守护线程
   对于非业务逻辑，例如监控数据上传，日志记录，这样做非常方便，但对于系统业务，这么做会导致未执行完成任务被丢弃。
2. 将线程池定义为springbean，交予spring容器管理其生命周期

@SpringBootApplication
@MapperScan("com.test.test.mapper")
public class TestApplication implements CommandLineRunner {

	public static void main(String[] args) {
		SpringApplication.run(TestApplication.class, args);
	}

	private static void run(ScheduledExecutorService executor) {
		executor.scheduleAtFixedRate(() -> {
			System.out.println("run");
		}, 0, 1, TimeUnit.SECONDS);
	}

	@Bean
	public ScheduledExecutorService executor() {
		return Executors.newScheduledThreadPool(1);
	}

	@Override
	public void run(String... args) throws Exception {
		ScheduledExecutorService executor = SpringUtil.getBean(ScheduledExecutorService.class);
		run(executor);
	}
}

效果
弊端：此类方式中，由于线程池的工作线程属于非守护线程，应用会等待所有任务执行完成后才关闭。由于容器已经关闭，数据库连接池已经释放，这时候任务再获取spring容器内容会报错，因此这种方案只适用于用户日志记录，监控等非业务功能，效果如下：

@SpringBootApplication
@MapperScan("com.test.test.mapper")
@Slf4j
public class TestApplication implements CommandLineRunner {
	public static void main(String[] args) {
		SpringApplication.run(TestApplication.class, args);
	}

	private static void run(ExecutorService executor) {
		executor.execute(() -> {
			log.info("=====start");
			try {
				TimeUnit.SECONDS.sleep(25);
				User user = SpringUtil.getBean(IUserService.class).findById(10L);
				log.info("用户信息:" + user);
			} catch (Exception ex) {
				ex.printStackTrace();
			}
			log.info("=========end");
		});
	}

	@Bean
	public ExecutorService executor() {
		return new ThreadPoolExecutor(
			10, 10, 10, TimeUnit.SECONDS,
			new ArrayBlockingQueue<>(1),
			r -> {
				Thread thread =new Thread(r);
				return thread;
			},
			new ThreadPoolExecutor.DiscardOldestPolicy());
	}

	@Override
	public void run(String... args) throws Exception {
		ExecutorService executor = SpringUtil.getBean(ExecutorService.class);
		run(executor);
	}
}

3.使用spring提供的ThreadPoolTaskExecutor线程池

@SpringBootApplication
@MapperScan("com.test.test.mapper")
@Slf4j
public class TestApplication implements CommandLineRunner {

	public static void main(String[] args) {
		SpringApplication.run(TestApplication.class, args);
	}

	private static void run(ThreadPoolTaskExecutor executor) {
		executor.execute(() -> {
			log.info("=====start");
			try {
				TimeUnit.SECONDS.sleep(25);
				User user = SpringUtil.getBean(IUserService.class).findById(10L);
				log.info("用户信息:" + user);
			} catch (Exception ex) {
				ex.printStackTrace();
			}
			log.info("=========end");
		});
	}

	@Bean
	public ThreadPoolTaskExecutor executor() {
		int core = Runtime.getRuntime().availableProcessors();
		ThreadPoolTaskExecutor executor = new ThreadPoolTaskExecutor();
		executor.setCorePoolSize(core > 3 ? core >> 1 : core);
		int maxSize = core + 2;
		executor.setMaxPoolSize(maxSize);
		//使用同步队列，避免任务进入等待队列排队导致耗时过长
		executor.setQueueCapacity(0);
		executor.setKeepAliveSeconds(30);
		executor.setWaitForTasksToCompleteOnShutdown(true);
		executor.setAwaitTerminationSeconds(25);
		executor.setThreadNamePrefix("async-");
		executor.setRejectedExecutionHandler(new ThreadPoolExecutor.CallerRunsPolicy());

		executor.initialize();

		return executor;
	}

	@Override
	public void run(String... args) throws Exception {
		ThreadPoolTaskExecutor executor = SpringUtil.getBean(ThreadPoolTaskExecutor.class);
		run(executor);
	}
}

从上图可以看到，应用会等待线程池任务执行完毕后才选择优雅关闭，因此对于异步业务任务，ThreadPoolTaskExecutor才是首选。
spring已经内置了ThreadPoolTaskExecutor 线程池实例，我们可以尝试修改其配置参数，简化代码来尝试，例如：

spring:
  task:
    execution:
      pool:
        queue-capacity: 0
        core-size: 2
        max-size: 16
        keep-alive: 30s
      thread-name-prefix: 'async-'
      shutdown:
        await-termination: true
        await-termination-period: 25s

@SpringBootApplication
@MapperScan("com.test.test.mapper")
@Slf4j
public class TestApplication implements CommandLineRunner {

	public static void main(String[] args) {
		SpringApplication.run(TestApplication.class, args);
	}

	private static void run(ThreadPoolTaskExecutor executor) {
		executor.execute(() -> {
			log.info("=====start");
			try {
				TimeUnit.SECONDS.sleep(25);
				User user = SpringUtil.getBean(IUserService.class).findById(10L);
				log.info("用户信息:" + user);
			} catch (Exception ex) {
				ex.printStackTrace();
			}
			log.info("=========end");
		});
	}

	@Override
	public void run(String... args) throws Exception {
		ThreadPoolTaskExecutor executor = SpringUtil.getBean(ThreadPoolTaskExecutor.class);
		run(executor);
	}
}

效果与上述手动创建效果一样，但是内置的ThreadPoolTaskExecutor线程池无法通过配置修改拒绝策略rejectedExecutionHandler，队列满了之后默认是AbortPolicy，会丢弃加入的任务并抛异常，spring内置此线程池的初衷在于为定时任务使用，例如@Scheduled。