如何優(yōu)雅的關(guān)閉 Java線程池

簡(jiǎn)介 在開(kāi)發(fā)中使用線程池去執(zhí)行異步任務(wù)是比較普遍的操作 ，然而雖然有些異步操作我們并不十分要求可靠性和實(shí)時(shí)性，但總歸業(yè)務(wù)還是需要的 。如果在每次的服務(wù)發(fā)版過(guò)程中，我們不去介入線程池的停機(jī)邏輯 ，那么很有可能就會(huì)造成線程池中隊(duì)列的任務(wù)還未執(zhí)行完成，自然就會(huì)造成數(shù)據(jù)的丟失。

探究

注意
，本文所有前提是對(duì)進(jìn)程進(jìn)行下線時(shí)使用的是kill -15

我們知道Spring已經(jīng)實(shí)現(xiàn)了自己的優(yōu)雅停機(jī)方案
，詳細(xì)請(qǐng)參考o(jì)rg.springframework.context.support.AbstractApplicationContext#registerShutdownHook，然后主要看調(diào)用的org.springframework.context.support.AbstractApplicationContext#doClose
 ， 在這個(gè)方法里定義了容器銷(xiāo)毀的執(zhí)行順序

protected void doClose() {   // Check whether an actual close attempt is necessary...  if (this.active.get() && this.closed.compareAndSet(false, true)) {    if (logger.isDebugEnabled()) {     logger.debug("Closing " + this);   }   LiveBeansView.unregisterApplicationContext(this);   try {     // Publish shutdown event.    publishEvent(new ContextClosedEvent(this));   }   catch (Throwable ex) {     logger.warn("Exception thrown from ApplicationListener handling ContextClosedEvent", ex);   }   // Stop all Lifecycle beans, to avoid delays during inpidual destruction.   if (this.lifecycleProcessor != null) {     try {      this.lifecycleProcessor.onClose();    }    catch (Throwable ex) {      logger.warn("Exception thrown from LifecycleProcessor on context close", ex);    }   }   // Destroy all cached singletons in the context's BeanFactory.   destroyBeans();   // Close the state of this context itself.   closeBeanFactory();   // Let subclasses do some final clean-up if they wish...   onClose();   // Reset local application listeners to pre-refresh state.   if (this.earlyApplicationListeners != null) {     this.applicationListeners.clear();    this.applicationListeners.addAll(this.earlyApplicationListeners);   }   // Switch to inactive.   this.active.set(false);  } }

我們先主要關(guān)注下destroyBeans這個(gè)方法
，看bean的銷(xiāo)毀邏輯是什么，然后看到了下面的一個(gè)bean的銷(xiāo)毀順序邏輯,具體方法在org.springframework.beans.factory.support.DefaultSingletonBeanRegistry#destroySingletons

private final MapdisposableBeans = new LinkedHashMap<>();  public void destroySingletons() {   if (logger.isTraceEnabled()) {    logger.trace("Destroying singletons in " + this);  }  synchronized (this.singletonObjects) {    this.singletonsCurrentlyInDestruction = true;  }  String[] disposableBeanNames;  synchronized (this.disposableBeans) {    disposableBeanNames = StringUtils.toStringArray(this.disposableBeans.keySet());  }  for (int i = disposableBeanNames.length - 1; i >= 0; i--) {    destroySingleton(disposableBeanNames[i]);  }  this.containedBeanMap.clear();  this.dependentBeanMap.clear();  this.dependenciesForBeanMap.clear();  clearSingletonCache(); }

可以看到最至關(guān)重要的就是一個(gè)屬性disposableBeans,這個(gè)屬性是一個(gè)LinkedHashMap， 因此屬性是有序的 ，所以銷(xiāo)毀的時(shí)候也是按照某種規(guī)則保持和放入一樣的順序進(jìn)行銷(xiāo)毀的 ，現(xiàn)在就是要確認(rèn)這個(gè)屬性里到底存的是什么