wen 求求你们别再用 kill -9 了，这才是 Spring Boot 停机的正确方式！！！
再谈为了提醒明知故犯（在一坑里迭倒两次不是不多见），由于业务系统中大量使用了spring Boot embedded tomcat的模式运行，在一些运维脚本中经常看到Linux 中 kill 指令，然而它的使用也有些讲究，要思考如何能做到优雅停机。
何为优雅关机
就是为确保应用关闭时，通知应用进程释放所占用的资源
- 线程池，shutdown（不接受新任务等待处理完）还是shutdownNow（调用
Thread.interrupt进行中断） - socket 链接，比如：netty、mq
- 告知注册中心快速下线（靠心跳机制客服早都跳起来了），比如：eureka
- 清理临时文件，比如：poi
- 各种堆内堆外内存释放
总之，进程强行终止会带来数据丢失或者终端无法恢复到正常状态，在分布式环境下还可能导致数据不一致的情况。
kill指令
kill -9 pid 可以模拟了一次系统宕机，系统断电等极端情况，而kill -15 pid 则是等待应用关闭，执行阻塞操作，有时候也会出现无法关闭应用的情况（线上理想情况下，是bug就该寻根溯源）
#查看jvm进程pid
jps
#列出所有信号名称
kill -l
# Windows下信号常量值
# 简称 全称 数值
# INT SIGINT 2 Ctrl+C中断
# ILL SIGILL 4 非法指令
# FPE SIGFPE 8 floating point exception(浮点异常)
# SEGV SIGSEGV 11 segment violation(段错误)
# TERM SIGTERM 5 Software termination signal from kill(Kill发出的软件终止)
# BREAK SIGBREAK 21 Ctrl-Break sequence(Ctrl+Break中断)
# ABRT SIGABRT 22 abnormal termination triggered by abort call(Abort)
#linux信号常量值
# 简称 全称 数值
# HUP SIGHUP 1 终端断线
# INT SIGINT 2 中断（同 Ctrl + C）
# QUIT SIGQUIT 3 退出（同 Ctrl + ）
# KILL SIGKILL 9 强制终止
# TERM SIGTERM 15 终止
# CONT SIGCONT 18 继续（与STOP相反， fg/bg命令）
# STOP SIGSTOP 19 暂停（同 Ctrl + Z）
#....
#可以理解为操作系统从内核级别强行杀死某个进程
kill -9 pid
#理解为发送一个通知，等待应用主动关闭
kill -15 pid
#也支持信号常量值全称或简写（就是去掉SIG后）
kill -l KILL
思考：jvm是如何接受处理linux信号量的？
当然是在jvm启动时就加载了自定义SignalHandler，关闭jvm时触发对应的handle。
public interface SignalHandler {
SignalHandler SIG_DFL = new NativeSignalHandler(0L);
SignalHandler SIG_IGN = new NativeSignalHandler(1L);
void handle(Signal var1);
}
class Terminator {
private static SignalHandler handler = null;
Terminator() {
}
//jvm设置SignalHandler，在System.initializeSystemClass中触发
static void setup() {
if (handler == null) {
SignalHandler var0 = new SignalHandler() {
public void handle(Signal var1) {
Shutdown.exit(var1.getNumber() + 128);//调用Shutdown.exit
}
};
handler = var0;
try {
Signal.handle(new Signal("INT"), var0);//中断时
} catch (IllegalArgumentException var3) {
;
}
try {
Signal.handle(new Signal("TERM"), var0);//终止时
} catch (IllegalArgumentException var2) {
;
}
}
}
}
Runtime.addShutdownHook
在了解Shutdown.exit之前，先看Runtime.getRuntime().addShutdownHook(shutdownHook);则是为jvm中增加一个关闭的钩子，当jvm关闭的时候调用。
public class Runtime {
public void addShutdownHook(Thread hook) {
SecurityManager sm = System.getSecurityManager();
if (sm != null) {
sm.checkPermission(new RuntimePermission("shutdownHooks"));
}
ApplicationShutdownHooks.add(hook);
}
}
class ApplicationShutdownHooks {
/* The set of registered hooks */
private static IdentityHashMap<Thread, Thread> hooks;
static synchronized void add(Thread hook) {
if(hooks == null)
throw new IllegalStateException("Shutdown in progress");
if (hook.isAlive())
throw new IllegalArgumentException("Hook already running");
if (hooks.containsKey(hook))
throw new IllegalArgumentException("Hook previously registered");
hooks.put(hook, hook);
}
}
//它含数据结构和逻辑管理虚拟机关闭序列
class Shutdown {
/* Shutdown 系列状态*/
private static final int RUNNING = 0;
private static final int HOOKS = 1;
private static final int FINALIZERS = 2;
private static int state = RUNNING;
/* 是否应该运行所以finalizers来exit? */
private static boolean runFinalizersOnExit = false;
// 系统关闭钩子注册一个预定义的插槽.
// 关闭钩子的列表如下:
// (0) Console restore hook
// (1) Application hooks
// (2) DeleteOnExit hook
private static final int MAX_SYSTEM_HOOKS = 10;
private static final Runnable[] hooks = new Runnable[MAX_SYSTEM_HOOKS];
// 当前运行关闭钩子的钩子的索引
private static int currentRunningHook = 0;
/* 前面的静态字段由这个锁保护 */
private static class Lock { };
private static Object lock = new Lock();
/* 为native halt方法提供锁对象 */
private static Object haltLock = new Lock();
static void add(int slot, boolean registerShutdownInProgress, Runnable hook) {
synchronized (lock) {
if (hooks[slot] != null)
throw new InternalError("Shutdown hook at slot " + slot + " already registered");
if (!registerShutdownInProgress) {//执行shutdown过程中不添加hook
if (state > RUNNING)//如果已经在执行shutdown操作不能添加hook
throw new IllegalStateException("Shutdown in progress");
} else {//如果hooks已经执行完毕不能再添加hook。如果正在执行hooks时，添加的槽点小于当前执行的槽点位置也不能添加
if (state > HOOKS || (state == HOOKS && slot <= currentRunningHook))
throw new IllegalStateException("Shutdown in progress");
}
hooks[slot] = hook;
}
}
/* 执行所有注册的hooks
*/
private static void runHooks() {
for (int i=0; i < MAX_SYSTEM_HOOKS; i++) {
try {
Runnable hook;
synchronized (lock) {
// acquire the lock to make sure the hook registered during
// shutdown is visible here.
currentRunningHook = i;
hook = hooks[i];
}
if (hook != null) hook.run();
} catch(Throwable t) {
if (t instanceof ThreadDeath) {
ThreadDeath td = (ThreadDeath)t;
throw td;
}
}
}
}
/* 关闭JVM的操作
*/
static void halt(int status) {
synchronized (haltLock) {
halt0(status);
}
}
//JNI方法
static native void halt0(int status);
// shutdown的执行顺序：runHooks > runFinalizersOnExit
private static void sequence() {
synchronized (lock) {
/* Guard against the possibility of a daemon thread invoking exit
* after DestroyJavaVM initiates the shutdown sequence
*/
if (state != HOOKS) return;
}
runHooks();
boolean rfoe;
synchronized (lock) {
state = FINALIZERS;
rfoe = runFinalizersOnExit;
}
if (rfoe) runAllFinalizers();
}
//Runtime.exit时执行，runHooks > runFinalizersOnExit > halt
static void exit(int status) {
boolean runMoreFinalizers = false;
synchronized (lock) {
if (status != 0) runFinalizersOnExit = false;
switch (state) {
case RUNNING: /* Initiate shutdown */
state = HOOKS;
break;
case HOOKS: /* Stall and halt */
break;
case FINALIZERS:
if (status != 0) {
/* Halt immediately on nonzero status */
halt(status);
} else {
/* Compatibility with old behavior:
* Run more finalizers and then halt
*/
runMoreFinalizers = runFinalizersOnExit;
}
break;
}
}
if (runMoreFinalizers) {
runAllFinalizers();
halt(status);
}
synchronized (Shutdown.class) {
/* Synchronize on the class object, causing any other thread
* that attempts to initiate shutdown to stall indefinitely
*/
sequence();
halt(status);
}
}
//shutdown操作，与exit不同的是不做halt操作(关闭JVM)
static void shutdown() {
synchronized (lock) {
switch (state) {
case RUNNING: /* Initiate shutdown */
state = HOOKS;
break;
case HOOKS: /* Stall and then return */
case FINALIZERS:
break;
}
}
synchronized (Shutdown.class) {
sequence();
}
}
}
spring 3.2.12
在spring中通过ContextClosedEvent事件来触发一些动作（可以拓展），主要通过LifecycleProcessor.onClose来做stopBeans。由此可见spring也基于jvm做了拓展。
推荐一个开源免费的 Spring Boot 最全教程：
https://github.com/javastacks/spring-boot-best-practice
public abstract class AbstractApplicationContext extends DefaultResourceLoader {
public void registerShutdownHook() {
if (this.shutdownHook == null) {
// No shutdown hook registered yet.
this.shutdownHook = new Thread() {
@Override
public void run() {
doClose();
}
};
Runtime.getRuntime().addShutdownHook(this.shutdownHook);
}
}
protected void doClose() {
boolean actuallyClose;
synchronized (this.activeMonitor) {
actuallyClose = this.active && !this.closed;
this.closed = true;
}
if (actuallyClose) {
if (logger.isInfoEnabled()) {
logger.info("Closing " + this);
}
LiveBeansView.unregisterApplicationContext(this);
try {
//发布应用内的关闭事件
publishEvent(new ContextClosedEvent(this));
}
catch (Throwable ex) {
logger.warn("Exception thrown from ApplicationListener handling ContextClosedEvent", ex);
}
// 停止所有的Lifecycle beans.
try {
getLifecycleProcessor().onClose();
}
catch (Throwable ex) {
logger.warn("Exception thrown from LifecycleProcessor on context close", ex);
}
// 销毁spring 的 BeanFactory可能会缓存单例的 Bean.
destroyBeans();
// 关闭当前应用上下文（BeanFactory）
closeBeanFactory();
// 执行子类的关闭逻辑
onClose();
synchronized (this.activeMonitor) {
this.active = false;
}
}
}
}
public interface LifecycleProcessor extends Lifecycle {
/**
* Notification of context refresh, e.g. for auto-starting components.
*/
void onRefresh();
/**
* Notification of context close phase, e.g. for auto-stopping components.
*/
void onClose();
}
spring boot
到这里就进入重点了，spring boot中有spring-boot-starter-actuator 模块提供了一个 restful 接口，用于优雅停机。执行请求 curl -X POST http://127.0.0.1:8088/shutdown ，待关闭成功则返回提示。
Spring Boot 基础就不介绍了，推荐看这个免费教程：
https://github.com/javastacks/spring-boot-best-practice
注：线上环境该url需要设置权限，可配合 spring-security使用或在nginx中限制内网访问
#启用shutdown
endpoints.shutdown.enabled=true
#禁用密码验证
endpoints.shutdown.sensitive=false
#可统一指定所有endpoints的路径
management.context-path=/manage
#指定管理端口和IP
management.port=8088
management.address=127.0.0.1
#开启shutdown的安全验证（spring-security）
endpoints.shutdown.sensitive=true
#验证用户名
security.user.name=admin
#验证密码
security.user.password=secret
#角色
management.security.role=SUPERUSER
spring boot的shutdown原理也不复杂，其实还是通过调用AbstractApplicationContext.close实现的。
@ConfigurationProperties(
prefix = "endpoints.shutdown"
)
public class ShutdownMvcEndpoint extends EndpointMvcAdapter {
public ShutdownMvcEndpoint(ShutdownEndpoint delegate) {
super(delegate);
}
//post请求
@PostMapping(
produces = {"application/vnd.spring-boot.actuator.v1+json", "application/json"}
)
@ResponseBody
public Object invoke() {
return !this.getDelegate().isEnabled() ? new ResponseEntity(Collections.singletonMap("message", "This endpoint is disabled"), HttpStatus.NOT_FOUND) : super.invoke();
}
}
@ConfigurationProperties(
prefix = "endpoints.shutdown"
)
public class ShutdownEndpoint extends AbstractEndpoint<Map<String, Object>> implements ApplicationContextAware {
private static final Map<String, Object> NO_CONTEXT_MESSAGE = Collections.unmodifiableMap(Collections.singletonMap("message", "No context to shutdown."));
private static final Map<String, Object> SHUTDOWN_MESSAGE = Collections.unmodifiableMap(Collections.singletonMap("message", "Shutting down, bye..."));
private ConfigurableApplicationContext context;
public ShutdownEndpoint() {
super("shutdown", true, false);
}
//执行关闭
public Map<String, Object> invoke() {
if (this.context == null) {
return NO_CONTEXT_MESSAGE;
} else {
boolean var6 = false;
Map var1;
class NamelessClass_1 implements Runnable {
NamelessClass_1() {
}
public void run() {
try {
Thread.sleep(500L);
} catch (InterruptedException var2) {
Thread.currentThread().interrupt();
}
//这个调用的就是AbstractApplicationContext.close
ShutdownEndpoint.this.context.close();
}
}
try {
var6 = true;
var1 = SHUTDOWN_MESSAGE;
var6 = false;
} finally {
if (var6) {
Thread thread = new Thread(new NamelessClass_1());
thread.setContextClassLoader(this.getClass().getClassLoader());
thread.start();
}
}
Thread thread = new Thread(new NamelessClass_1());
thread.setContextClassLoader(this.getClass().getClassLoader());
thread.start();
return var1;
}
}
}
版权声明：本文为CSDN博主「布道」的原创文章，遵循CC 4.0 BY-SA版权协议，转载请附上原文出处链接及本声明。原文链接：https://blog.csdn.net/alex_xfboy/article/details/90404691
近期热文推荐：
1.1,000+ 道 Java面试题及答案整理(2022最新版)
2.劲爆！Java 协程要来了。。。
3.Spring Boot 2.x 教程，太全了！
4.别再写满屏的爆爆爆炸类了，试试装饰器模式，这才是优雅的方式！！
5.《Java开发手册（嵩山版）》最新发布，速速下载！
觉得不错，别忘了随手点赞+转发哦！
