求求你们别再用 kill -9 了，这才是 Spring Boot 停机的正确方式！

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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。

1. 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。

2. 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 > 基于 Spring Cloud Alibaba + Gateway + Nacos + RocketMQ + Vue & Element 实现的后台管理系统 + 用户小程序，支持 RBAC 动态权限、多租户、数据权限、工作流、三方登录、支付、短信、商城等功能 > > * 项目地址： //github.com/YunaiV/yudao-cloud> > * 视频教程： //doc.iocoder.cn/video/> # 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);     voidhandle(Signal var1); } class Terminator{     privatestatic SignalHandler handler = null;     Terminator() {     }     //jvm设置SignalHandler，在System.initializeSystemClass中触发     staticvoidsetup(){         if (handler == null) {             SignalHandler var0 = new SignalHandler() {                 publicvoidhandle(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。

publicclassRuntime{     publicvoidaddShutdownHook(Thread hook){         SecurityManager sm = System.getSecurityManager();         if (sm != null) {             sm.checkPermission(new RuntimePermission("shutdownHooks"));         }         ApplicationShutdownHooks.add(hook);     } } classApplicationShutdownHooks{     /* The set of registered hooks */     privatestatic IdentityHashMap hooks;     staticsynchronizedvoidadd(Thread hook){         if(hooks == null)             thrownew IllegalStateException("Shutdown in progress");         if (hook.isAlive())             thrownew IllegalArgumentException("Hook already running");         if (hooks.containsKey(hook))             thrownew 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 classShutdown{     /* Shutdown 系列状态*/     privatestaticfinalint RUNNING = 0;     privatestaticfinalint HOOKS = 1;     privatestaticfinalint FINALIZERS = 2;     privatestaticint state = RUNNING;     /* 是否应该运行所以finalizers来exit? */     privatestaticboolean 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     privatestaticfinalint MAX_SYSTEM_HOOKS = 10;     privatestaticfinal Runnable[] hooks = new Runnable[MAX_SYSTEM_HOOKS];     // 当前运行关闭钩子的钩子的索引     privatestaticint currentRunningHook = 0;     /* 前面的静态字段由这个锁保护 */     privatestaticclassLock{ };     privatestatic Object lock = new Lock();     /* 为native halt方法提供锁对象 */     privatestatic Object haltLock = new Lock();     staticvoidadd(int slot, boolean registerShutdownInProgress, Runnable hook){         synchronized (lock) {             if (hooks[slot] != null)                 thrownew 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                     thrownew 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))                     thrownew IllegalStateException("Shutdown in progress");             }             hooks[slot] = hook;         }     }     /* 执行所有注册的hooks      */     privatestaticvoidrunHooks(){         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      */     staticvoidhalt(int status){         synchronized (haltLock) {             halt0(status);         }     }     //JNI方法     staticnativevoidhalt0(int status);     // shutdown的执行顺序：runHooks > runFinalizersOnExit     privatestaticvoidsequence(){         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     staticvoidexit(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)     staticvoidshutdown(){         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。

publicabstractclassAbstractApplicationContextextendsDefaultResourceLoader{ publicvoidregisterShutdownHook(){ if (this.shutdownHook == null) {    // No shutdown hook registered yet.    this.shutdownHook = new Thread() {     @Override     publicvoidrun(){      doClose();     }    };    Runtime.getRuntime().addShutdownHook(this.shutdownHook);   }  } protectedvoiddoClose(){ 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;    }   }  }  } publicinterfaceLifecycleProcessorextendsLifecycle{ /**   * Notification of context refresh, e.g. for auto-starting components.   */ voidonRefresh(); /**   * Notification of context close phase, e.g. for auto-stopping components.   */ voidonClose(); }

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。

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" ) publicclassShutdownMvcEndpointextendsEndpointMvcAdapter{     publicShutdownMvcEndpoint(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" ) publicclassShutdownEndpointextendsAbstractEndpoint

 > implementsApplicationContextAware{     privatestaticfinal Map NO_CONTEXT_MESSAGE = Collections.unmodifiableMap(Collections.singletonMap( "message", "No context to shutdown."));     privatestaticfinal Map SHUTDOWN_MESSAGE = Collections.unmodifiableMap(Collections.singletonMap( "message", "Shutting down, bye..."));     private ConfigurableApplicationContext context;     publicShutdownEndpoint(){         super("shutdown", true, false);     }     //执行关闭     public Map   invoke(){         if (this.context == null) {             return NO_CONTEXT_MESSAGE;         } else {             boolean var6 = false;             Map var1;             classNamelessClass_1implementsRunnable{                 NamelessClass_1() {                 }                 publicvoidrun(){                     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;         }     } }

引用资料：https://linux.die.net/man/1/kill

作者：布道

来源：https://juejin.cn/post/7394073179483947008

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