Tomcat处理请求的线程模型是什么
小编给大家分享一下Tomcat处理请求的线程模型是什么，相信大部分人都还不怎么了解，因此分享这篇文章给大家参考一下，希望大家阅读完这篇文章后大有收获，下面让我们一起去了解一下吧！
一、前言
JAVA后端项目，运行在容器tomcat中，由于现在springboot的内置tomcat容器，其默认配置屏蔽了很多对tomcat的认知，但是对tomcat的学习和认识是比较重要的，所以专门查资料加深了理解，本文主要讨论在springboot集成下的tomcat9的请求过程，线程模型为NIO。
二、tomcat结构
找了张结构图，每个模块的意思和作用就不详解了，可以搜其他文章
三、探讨tomcat是如何处理请求
自己画了一个connector的结构
1、初始化
在springboot启动后，org.springframework.context.support.AbstractApplicationContext#finishRefresh，这里进去调用org.springframework.boot.web.servlet.context.WebServerStartStopLifecycle.start()方法启动TomcatWebServer，初始化tomcat。
通过这样的调用链到达org.apache.tomcat.util.net.NioEndpoint#startInternal(),进行初始化Endpoint中的Acceptor和Poller，这两者都实现了Runnable接口，初始化后就通过线程start启动了。
2、如何处理客户端请求
Acceptor： 接收器，作用是接受scoket网络请求，并调用setSocketOptions()封装成为NioSocketWrapper，并注册到Poller的events中。注意查看run方法org.apache.tomcat.util.net.Acceptor#run
@Override public void run() { int errorDelay = 0; try { // Loop until we receive a shutdown command while (!stopCalled) { // Loop if endpoint is paused while (endpoint.isPaused() && !stopCalled) { state = AcceptorState.PAUSED; try { Thread.sleep(50); } catch (InterruptedException e) { // Ignore } } if (stopCalled) { break; } state = AcceptorState.RUNNING; try { //if we have reached max connections, wait endpoint.countUpOrAwaitConnection(); // Endpoint might have been paused while waiting for latch // If that is the case, don't accept new connections if (endpoint.isPaused()) { continue; } U socket = null; try { // 等待下一个请求进来 socket = endpoint.serverSocketAccept(); } catch (Exception ioe) { // We didn't get a socket endpoint.countDownConnection(); if (endpoint.isRunning()) { // Introduce delay if necessary errorDelay = handleExceptionWithDelay(errorDelay); // re-throw throw ioe; } else { break; } } // Successful accept, reset the error delay errorDelay = 0; // Configure the socket if (!stopCalled && !endpoint.isPaused()) { // 注册socket到Poller，生成PollerEvent事件 if (!endpoint.setSocketOptions(socket)) { endpoint.closeSocket(socket); } } else { endpoint.destroySocket(socket); } } catch (Throwable t) { ExceptionUtils.handleThrowable(t); String msg = sm.getString("endpoint.accept.fail"); // APR specific. // Could push this down but not sure it is worth the trouble. if (t instanceof Error) { Error e = (Error) t; if (e.getError() == 233) { // Not an error on HP-UX so log as a warning // so it can be filtered out on that platform // See bug 50273 log.warn(msg, t); } else { log.error(msg, t); } } else { log.error(msg, t); } } } } finally { stopLatch.countDown(); } state = AcceptorState.ENDED; }Poller：轮询器，轮询是否有事件达到，有请求事件到达后，以NIO的处理方式，查询Selector取出所有请求，遍历每个请求的需求，分配给Executor线程池执行。查看org.apache.tomcat.util.net.NioEndpoint.Poller#run()
public void run() { // Loop until destroy() is called while (true) { boolean hasEvents = false; try { if (!close) { hasEvents = events(); if (wakeupCounter.getAndSet(-1) > 0) { // If we are here, means we have other stuff to do // Do a non blocking select keyCount = selector.selectNow(); } else { keyCount = selector.select(selectorTimeout); } wakeupCounter.set(0); } if (close) { events(); timeout(0, false); try { selector.close(); } catch (IOException ioe) { log.error(sm.getString("endpoint.nio.selectorCloseFail"), ioe); } break; } // Either we timed out or we woke up, process events first if (keyCount == 0) { hasEvents = (hasEvents | events()); } } catch (Throwable x) { ExceptionUtils.handleThrowable(x); log.error(sm.getString("endpoint.nio.selectorLoopError"), x); continue; } //查询selector取出所有请求 Iterator iterator = keyCount > 0 ? selector.selectedKeys().iterator() : null; // Walk through the collection of ready keys and dispatch // any active event. while (iterator != null && iterator.hasNext()) { SelectionKey sk = iterator.next(); iterator.remove(); NioSocketWrapper socketWrapper = (NioSocketWrapper) sk.attachment(); //处理请求key if (socketWrapper != null) { processKey(sk, socketWrapper); } } // Process timeouts timeout(keyCount,hasEvents); } getStopLatch().countDown(); } 请求过程大致如下图：
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