再談為了提醒明知故犯（在一坑里迭倒兩次不是不多見），由于業(yè)務(wù)系統(tǒng)中大量使用了spring Boot embedded tomcat的模式運(yùn)行，在一些運(yùn)維腳本中經(jīng)?？吹?a href="http://hljzzgx.com/v/tag/538/" target="_blank">Linux 中 kill 指令，然而它的使用也有些講究，要思考如何能做到優(yōu)雅停機(jī)。

何為優(yōu)雅關(guān)機(jī)

就是為確保應(yīng)用關(guān)閉時(shí)，通知應(yīng)用進(jìn)程釋放所占用的資源

• 線程池，shutdown（不接受新任務(wù)等待處理完）還是shutdownNow（調(diào)用 Thread.interrupt進(jìn)行中斷）
• socket 鏈接，比如：netty、mq
• 告知注冊(cè)中心快速下線（靠心跳機(jī)制客服早都跳起來了），比如：eureka
• 清理臨時(shí)文件，比如：poi
• 各種堆內(nèi)堆外內(nèi)存釋放

總之，進(jìn)程強(qiáng)行終止會(huì)帶來數(shù)據(jù)丟失或者終端無法恢復(fù)到正常狀態(tài)，在分布式環(huán)境下還可能導(dǎo)致數(shù)據(jù)不一致的情況。

基于 Spring Boot + MyBatis Plus + Vue & Element 實(shí)現(xiàn)的后臺(tái)管理系統(tǒng) + 用戶小程序，支持 RBAC 動(dòng)態(tài)權(quán)限、多租戶、數(shù)據(jù)權(quán)限、工作流、三方登錄、支付、短信、商城等功能

• 項(xiàng)目地址：https://github.com/YunaiV/ruoyi-vue-pro
• 視頻教程：https://doc.iocoder.cn/video/

kill指令

kill -9 pid 可以模擬了一次系統(tǒng)宕機(jī)，系統(tǒng)斷電等極端情況，而kill -15 pid 則是等待應(yīng)用關(guān)閉，執(zhí)行阻塞操作，有時(shí)候也會(huì)出現(xiàn)無法關(guān)閉應(yīng)用的情況（線上理想情況下，是bug就該尋根溯源）

#查看jvm進(jìn)程pid
jps
#列出所有信號(hào)名稱
kill-l


>基于SpringCloudAlibaba+Gateway+Nacos+RocketMQ+Vue&Element實(shí)現(xiàn)的后臺(tái)管理系統(tǒng)+用戶小程序，支持RBAC動(dòng)態(tài)權(quán)限、多租戶、數(shù)據(jù)權(quán)限、工作流、三方登錄、支付、短信、商城等功能
>
>*項(xiàng)目地址：//github.com/YunaiV/yudao-cloud>
>*視頻教程：//doc.iocoder.cn/video/>

#Windows下信號(hào)常量值
#簡稱全稱數(shù)值
#INTSIGINT2Ctrl+C中斷
#ILLSIGILL4非法指令
#FPESIGFPE8floatingpointexception(浮點(diǎn)異常)
#SEGVSIGSEGV11segmentviolation(段錯(cuò)誤)
#TERMSIGTERM5Softwareterminationsignalfromkill(Kill發(fā)出的軟件終止)
#BREAKSIGBREAK21Ctrl-Breaksequence(Ctrl+Break中斷)
#ABRTSIGABRT22abnormalterminationtriggeredbyabortcall(Abort)

#linux信號(hào)常量值
#簡稱全稱數(shù)值
#HUPSIGHUP1終端斷線
#INTSIGINT2中斷（同Ctrl+C）
#QUITSIGQUIT3退出（同Ctrl+）
#KILLSIGKILL9強(qiáng)制終止
#TERMSIGTERM15終止
#CONTSIGCONT18繼續(xù)（與STOP相反，fg/bg命令）
#STOPSIGSTOP19暫停（同Ctrl+Z）
#....

#可以理解為操作系統(tǒng)從內(nèi)核級(jí)別強(qiáng)行殺死某個(gè)進(jìn)程
kill-9pid
#理解為發(fā)送一個(gè)通知，等待應(yīng)用主動(dòng)關(guān)閉
kill-15pid
#也支持信號(hào)常量值全稱或簡寫（就是去掉SIG后）
kill-lKILL

思考：jvm是如何接受處理linux信號(hào)量的？

當(dāng)然是在jvm啟動(dòng)時(shí)就加載了自定義SignalHandler，關(guān)閉jvm時(shí)觸發(fā)對(duì)應(yīng)的handle。

publicinterfaceSignalHandler{
SignalHandlerSIG_DFL=newNativeSignalHandler(0L);
SignalHandlerSIG_IGN=newNativeSignalHandler(1L);

voidhandle(Signalvar1);
}
classTerminator{
privatestaticSignalHandlerhandler=null;

Terminator(){
}
//jvm設(shè)置SignalHandler，在System.initializeSystemClass中觸發(fā)
staticvoidsetup(){
if(handler==null){
SignalHandlervar0=newSignalHandler(){
publicvoidhandle(Signalvar1){
Shutdown.exit(var1.getNumber()+128);//調(diào)用Shutdown.exit
}
};
handler=var0;

try{
Signal.handle(newSignal("INT"),var0);//中斷時(shí)
}catch(IllegalArgumentExceptionvar3){
;
}

try{
Signal.handle(newSignal("TERM"),var0);//終止時(shí)
}catch(IllegalArgumentExceptionvar2){
;
}

}
}
}

Runtime.addShutdownHook

在了解Shutdown.exit之前，先看Runtime.getRuntime().addShutdownHook(shutdownHook);則是為jvm中增加一個(gè)關(guān)閉的鉤子，當(dāng)jvm關(guān)閉的時(shí)候調(diào)用。

publicclassRuntime{
publicvoidaddShutdownHook(Threadhook){
SecurityManagersm=System.getSecurityManager();
if(sm!=null){
sm.checkPermission(newRuntimePermission("shutdownHooks"));
}
ApplicationShutdownHooks.add(hook);
}
}
classApplicationShutdownHooks{
/*Thesetofregisteredhooks*/
privatestaticIdentityHashMaphooks;
staticsynchronizedvoidadd(Threadhook){
if(hooks==null)
thrownewIllegalStateException("Shutdowninprogress");

if(hook.isAlive())
thrownewIllegalArgumentException("Hookalreadyrunning");

if(hooks.containsKey(hook))
thrownewIllegalArgumentException("Hookpreviouslyregistered");

hooks.put(hook,hook);
}
}
//它含數(shù)據(jù)結(jié)構(gòu)和邏輯管理虛擬機(jī)關(guān)閉序列
classShutdown{
/*Shutdown系列狀態(tài)*/
privatestaticfinalintRUNNING=0;
privatestaticfinalintHOOKS=1;
privatestaticfinalintFINALIZERS=2;
privatestaticintstate=RUNNING;
/*是否應(yīng)該運(yùn)行所以finalizers來exit?*/
privatestaticbooleanrunFinalizersOnExit=false;
//系統(tǒng)關(guān)閉鉤子注冊(cè)一個(gè)預(yù)定義的插槽.
//關(guān)閉鉤子的列表如下:
//(0)Consolerestorehook
//(1)Applicationhooks
//(2)DeleteOnExithook
privatestaticfinalintMAX_SYSTEM_HOOKS=10;
privatestaticfinalRunnable[]hooks=newRunnable[MAX_SYSTEM_HOOKS];
//當(dāng)前運(yùn)行關(guān)閉鉤子的鉤子的索引
privatestaticintcurrentRunningHook=0;
/*前面的靜態(tài)字段由這個(gè)鎖保護(hù)*/
privatestaticclassLock{};
privatestaticObjectlock=newLock();

/*為nativehalt方法提供鎖對(duì)象*/
privatestaticObjecthaltLock=newLock();

staticvoidadd(intslot,booleanregisterShutdownInProgress,Runnablehook){
synchronized(lock){
if(hooks[slot]!=null)
thrownewInternalError("Shutdownhookatslot"+slot+"alreadyregistered");

if(!registerShutdownInProgress){//執(zhí)行shutdown過程中不添加hook
if(state>RUNNING)//如果已經(jīng)在執(zhí)行shutdown操作不能添加hook
thrownewIllegalStateException("Shutdowninprogress");
}else{//如果hooks已經(jīng)執(zhí)行完畢不能再添加hook。如果正在執(zhí)行hooks時(shí)，添加的槽點(diǎn)小于當(dāng)前執(zhí)行的槽點(diǎn)位置也不能添加
if(state>HOOKS||(state==HOOKS&&slot<=?currentRunningHook))
????????????????????thrownewIllegalStateException("Shutdowninprogress");
}

hooks[slot]=hook;
}
}
/*執(zhí)行所有注冊(cè)的hooks
*/
privatestaticvoidrunHooks(){
for(inti=0;itry{
Runnablehook;
synchronized(lock){
//acquirethelocktomakesurethehookregisteredduring
//shutdownisvisiblehere.
currentRunningHook=i;
hook=hooks[i];
}
if(hook!=null)hook.run();
}catch(Throwablet){
if(tinstanceofThreadDeath){
ThreadDeathtd=(ThreadDeath)t;
throwtd;
}
}
}
}
/*關(guān)閉JVM的操作
*/
staticvoidhalt(intstatus){
synchronized(haltLock){
halt0(status);
}
}
//JNI方法
staticnativevoidhalt0(intstatus);
//shutdown的執(zhí)行順序：runHooks>runFinalizersOnExit
privatestaticvoidsequence(){
synchronized(lock){
/*Guardagainstthepossibilityofadaemonthreadinvokingexit
*afterDestroyJavaVMinitiatestheshutdownsequence
*/
if(state!=HOOKS)return;
}
runHooks();
booleanrfoe;
synchronized(lock){
state=FINALIZERS;
rfoe=runFinalizersOnExit;
}
if(rfoe)runAllFinalizers();
}
//Runtime.exit時(shí)執(zhí)行，runHooks>runFinalizersOnExit>halt
staticvoidexit(intstatus){
booleanrunMoreFinalizers=false;
synchronized(lock){
if(status!=0)runFinalizersOnExit=false;
switch(state){
caseRUNNING:/*Initiateshutdown*/
state=HOOKS;
break;
caseHOOKS:/*Stallandhalt*/
break;
caseFINALIZERS:
if(status!=0){
/*Haltimmediatelyonnonzerostatus*/
halt(status);
}else{
/*Compatibilitywitholdbehavior:
*Runmorefinalizersandthenhalt
*/
runMoreFinalizers=runFinalizersOnExit;
}
break;
}
}
if(runMoreFinalizers){
runAllFinalizers();
halt(status);
}
synchronized(Shutdown.class){
/*Synchronizeontheclassobject,causinganyotherthread
*thatattemptstoinitiateshutdowntostallindefinitely
*/
sequence();
halt(status);
}
}
//shutdown操作，與exit不同的是不做halt操作(關(guān)閉JVM)
staticvoidshutdown(){
synchronized(lock){
switch(state){
caseRUNNING:/*Initiateshutdown*/
state=HOOKS;
break;
caseHOOKS:/*Stallandthenreturn*/
caseFINALIZERS:
break;
}
}
synchronized(Shutdown.class){
sequence();
}
}
}

spring 3.2.12

在spring中通過ContextClosedEvent事件來觸發(fā)一些動(dòng)作（可以拓展），主要通過LifecycleProcessor.onClose來做stopBeans。由此可見spring也基于jvm做了拓展。

publicabstractclassAbstractApplicationContextextendsDefaultResourceLoader{
publicvoidregisterShutdownHook(){
if(this.shutdownHook==null){
//Noshutdownhookregisteredyet.
this.shutdownHook=newThread(){
@Override
publicvoidrun(){
doClose();
}
};
Runtime.getRuntime().addShutdownHook(this.shutdownHook);
}
}
protectedvoiddoClose(){
booleanactuallyClose;
synchronized(this.activeMonitor){
actuallyClose=this.active&&!this.closed;
this.closed=true;
}

if(actuallyClose){
if(logger.isInfoEnabled()){
logger.info("Closing"+this);
}

LiveBeansView.unregisterApplicationContext(this);

try{
//發(fā)布應(yīng)用內(nèi)的關(guān)閉事件
publishEvent(newContextClosedEvent(this));
}
catch(Throwableex){
logger.warn("ExceptionthrownfromApplicationListenerhandlingContextClosedEvent",ex);
}

//停止所有的Lifecyclebeans.
try{
getLifecycleProcessor().onClose();
}
catch(Throwableex){
logger.warn("ExceptionthrownfromLifecycleProcessoroncontextclose",ex);
}

//銷毀spring的BeanFactory可能會(huì)緩存單例的Bean.
destroyBeans();

//關(guān)閉當(dāng)前應(yīng)用上下文（BeanFactory）
closeBeanFactory();

//執(zhí)行子類的關(guān)閉邏輯
onClose();

synchronized(this.activeMonitor){
this.active=false;
}
}
}
}
publicinterfaceLifecycleProcessorextendsLifecycle{
/**
*Notificationofcontextrefresh,e.g.forauto-startingcomponents.
*/
voidonRefresh();

/**
*Notificationofcontextclosephase,e.g.forauto-stoppingcomponents.
*/
voidonClose();
}

spring boot

到這里就進(jìn)入重點(diǎn)了，spring boot中有spring-boot-starter-actuator 模塊提供了一個(gè) restful 接口，用于優(yōu)雅停機(jī)。執(zhí)行請(qǐng)求 curl -X POST http://127.0.0.1:8088/shutdown ，待關(guān)閉成功則返回提示。

注：線上環(huán)境該url需要設(shè)置權(quán)限，可配合 spring-security使用或在nginx中限制內(nèi)網(wǎng)訪問

#啟用shutdown
endpoints.shutdown.enabled=true
#禁用密碼驗(yàn)證
endpoints.shutdown.sensitive=false
#可統(tǒng)一指定所有endpoints的路徑
management.context-path=/manage
#指定管理端口和IP
management.port=8088
management.address=127.0.0.1

#開啟shutdown的安全驗(yàn)證（spring-security）
endpoints.shutdown.sensitive=true
#驗(yàn)證用戶名
security.user.name=admin
#驗(yàn)證密碼
security.user.password=secret
#角色
management.security.role=SUPERUSER

spring boot的shutdown原理也不復(fù)雜，其實(shí)還是通過調(diào)用AbstractApplicationContext.close實(shí)現(xiàn)的。

@ConfigurationProperties(
prefix="endpoints.shutdown"
)
publicclassShutdownMvcEndpointextendsEndpointMvcAdapter{
publicShutdownMvcEndpoint(ShutdownEndpointdelegate){
super(delegate);
}
//post請(qǐng)求
@PostMapping(
produces={"application/vnd.spring-boot.actuator.v1+json","application/json"}
)
@ResponseBody
publicObjectinvoke(){
return!this.getDelegate().isEnabled()?newResponseEntity(Collections.singletonMap("message","Thisendpointisdisabled"),HttpStatus.NOT_FOUND):super.invoke();
}
}
@ConfigurationProperties(
prefix="endpoints.shutdown"
)
publicclassShutdownEndpointextendsAbstractEndpoint<Map<String,Object>>implementsApplicationContextAware{
privatestaticfinalMapNO_CONTEXT_MESSAGE=Collections.unmodifiableMap(Collections.singletonMap("message","Nocontexttoshutdown."));
privatestaticfinalMapSHUTDOWN_MESSAGE=Collections.unmodifiableMap(Collections.singletonMap("message","Shuttingdown,bye..."));
privateConfigurableApplicationContextcontext;

publicShutdownEndpoint(){
super("shutdown",true,false);
}
//執(zhí)行關(guān)閉
publicMapinvoke(){
if(this.context==null){
returnNO_CONTEXT_MESSAGE;
}else{
booleanvar6=false;

Mapvar1;

classNamelessClass_1implementsRunnable{
NamelessClass_1(){
}

publicvoidrun(){
try{
Thread.sleep(500L);
}catch(InterruptedExceptionvar2){
Thread.currentThread().interrupt();
}
//這個(gè)調(diào)用的就是AbstractApplicationContext.close
ShutdownEndpoint.this.context.close();
}
}

try{
var6=true;
var1=SHUTDOWN_MESSAGE;
var6=false;
}finally{
if(var6){
Threadthread=newThread(newNamelessClass_1());
thread.setContextClassLoader(this.getClass().getClassLoader());
thread.start();
}
}

Threadthread=newThread(newNamelessClass_1());
thread.setContextClassLoader(this.getClass().getClassLoader());
thread.start();
returnvar1;
}
}
}

審核編輯 ：李倩