介绍
作为常用的http协议服务器，tomcat应用非常广泛。tomcat也是遵循servelt协议的，servelt协议可以让服务器与真实服务逻辑代码进行解耦。各自只需要关注servlet协议即可。
对于tomcat是如何作为一个高性能的服务器的呢？你是不是也会有这样的疑问？
tomcat是如何接收网络请求？
如何做到高性能的http协议服务器？
tomcat从8.0往后开始使用了nio非阻塞io模型，提高了吞吐量，本文的源码是tomcat 9.0.48版本
接收socket请求
org.apache.tomcat.util.net.acceptor实现了runnable接口，在一个单独的线程中以死循环的方式一直进行socket的监听
线程的初始化及启动是在方法org.apache.tomcat.util.net.abstractendpoint#startacceptorthread
有个很重要的属性org.apache.tomcat.util.net.abstractendpoint；同时实现了run方法，方法中主要有以下功能：
- 请求最大连接数限制： 最大为 8*1024；请你注意到达最大连接数后操作系统底层还是会接收客户端连接，但用户层已经不再接收
- 获取
socketchannel
public void run() {
int errordelay = 0;
try {
// loop until we receive a shutdown command
while (!stopcalled) {
...
if (stopcalled) {
break;
}
state = acceptorstate.running;
try {
//if we have reached max connections, wait
// 如果连接超过了 8*1024，则线程阻塞等待; 是使用org.apache.tomcat.util.threads.limitlatch类实现了分享锁(内部实现了abstractqueuedsynchronizer)
// 请你注意到达最大连接数后操作系统底层还是会接收客户端连接，但用户层已经不再接收。
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 {
// accept the next incoming connection from the server
// socket
// 抽象方法，不同的endpoint有不同的实现方法。nioendpoint为例，实现方法为serversock.accept()，这个方法主要看serversock实例化时如果为阻塞，accept方法为阻塞；反之为立即返回，如果没有socket链接，则为null
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()) {
// setsocketoptions() will hand the socket off to
// an appropriate processor if successful
// endpoint类的抽象方法，不同的endpoint有不同的实现。处理获取到的socketchannel链接，如果该socket链接能正常处理，那么该方法会返回true，否则为false
if (!endpoint.setsocketoptions(socket)) {
endpoint.closesocket(socket);
}
} else {
endpoint.destroysocket(socket);
}
} catch (throwable t) {
...
}
}
} finally {
stoplatch.countdown();
}
state = acceptorstate.ended;
}
再来看下org.apache.tomcat.util.net.nioendpoint#setsocketoptions方法的具体实现(nioendpoint为例)
这个方法中主要做的事：
- 创建niochannel
- 设置socket为非阻塞
- 将socket添加到poller的队列中
protected boolean setsocketoptions(socketchannel socket) {
niosocketwrapper socketwrapper = null;
try {
// allocate channel and wrapper
// 优先使用已有的缓存niochannel
niochannel channel = null;
if (niochannels != null) {
channel = niochannels.pop();
}
if (channel == null) {
socketbufferhandler bufhandler = new socketbufferhandler(
socketproperties.getappreadbufsize(),
socketproperties.getappwritebufsize(),
socketproperties.getdirectbuffer());
if (issslenabled()) {
channel = new secureniochannel(bufhandler, this);
} else {
channel = new niochannel(bufhandler);
}
}
// 将nioendpoint与niochannel进行包装
niosocketwrapper newwrapper = new niosocketwrapper(channel, this);
channel.reset(socket, newwrapper);
connections.put(socket, newwrapper);
socketwrapper = newwrapper;
// set socket properties
// disable blocking, polling will be used
// 设置当前链接的socket为非阻塞
socket.configureblocking(false);
if (getunixdomainsocketpath() == null) {
socketproperties.setproperties(socket.socket());
}
socketwrapper.setreadtimeout(getconnectiontimeout());
socketwrapper.setwritetimeout(getconnectiontimeout());
socketwrapper.setkeepaliveleft(nioendpoint.this.getmaxkeepaliverequests());
// 将包装后的niochannel与nioendpoint进行注册，注册到poller，将对应的socket包装类添加到poller的队列中，同时唤醒selector
poller.register(socketwrapper);
return true;
} catch (throwable t) {
exceptionutils.handlethrowable(t);
try {
log.error(sm.getstring("endpoint.socketoptionserror"), t);
} catch (throwable tt) {
exceptionutils.handlethrowable(tt);
}
if (socketwrapper == null) {
destroysocket(socket);
}
}
// tell to close the socket if needed
return false;
}
socket请求轮询
上一小节是接收到了socket请求，进行包装之后，将socket添加到了poller的队列上，并可能唤醒了selector，本小节就来看看，poller是如何进行socket的轮询的。
首先org.apache.tomcat.util.net.nioendpoint.poller也是实现了runnable接口，是一个可以单独启动的线程
初始化及启动是在org.apache.tomcat.util.net.nioendpoint#startinternal
重要的属性：
java.nio.channels.selector：在poller对象初始化的时候，就会启动轮询器synchronizedqueue<pollerevent>：同步的事件队列
再来看下具体处理逻辑，run方法的源码
public void run() {
// loop until destroy() is called
while (true) {
boolean hasevents = false;
try {
if (!close) {
// 去synchronizedqueue事件队列中拉去，看是否已经有了事件，如果有，则返回true
// 如果从队列中拉取到了event(即上一步将niosocketwrapper封装为pollerevent添加到次队列中)，将socketchannel注册到selector上，标记为selectionkey.op_read，添加处理函数attachment(为accetpor添加到poller时的
// niosocketwrapper)
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;
}
iterator<selectionkey> iterator =
keycount > 0 ? selector.selectedkeys().iterator() : null;
// walk through the collection of ready keys and dispatch
// any active event.
// selector轮询获取已经注册的事件，如果有事件准备好，此时通过selectkeys方法就能拿到对应的事件
while (iterator != null && iterator.hasnext()) {
selectionkey sk = iterator.next();
// 获取到事件后，从迭代器删除事件，防止事件重复轮询
iterator.remove();
// 获取事件的处理器，这个attachment是在event()方法中注册的，后续这个事件的处理，就交给这个wrapper去处理
niosocketwrapper socketwrapper = (niosocketwrapper) sk.attachment();
// attachment may be null if another thread has called
// cancelledkey()
if (socketwrapper != null) {
processkey(sk, socketwrapper);
}
}
// process timeouts
timeout(keycount,hasevents);
}
getstoplatch().countdown();
}
在这里，有一个很重要的方法，org.apache.tomcat.util.net.nioendpoint.poller#events()，他是从poller的事件队列中获取acceptor接收到的可用socket，并将其注册到selector上
/**
* processes events in the event queue of the poller.
*
* @return <code>true</code> if some events were processed,
* <code>false</code> if queue was empty
*/
public boolean events() {
boolean result = false;
pollerevent pe = null;
// 如果acceptor将socket添加到队列中，那么events.poll()方法就能拿到对应的事件，否则拿不到就返回false
for (int i = 0, size = events.size(); i < size && (pe = events.poll()) != null; i++ ) {
result = true;
niosocketwrapper socketwrapper = pe.getsocketwrapper();
socketchannel sc = socketwrapper.getsocket().getiochannel();
int interestops = pe.getinterestops();
if (sc == null) {
log.warn(sm.getstring("endpoint.nio.nullsocketchannel"));
socketwrapper.close();
} else if (interestops == op_register) {
// 如果是acceptor刚添加到队列中的事件，那么此时的ops就是op_register
try {，
// 将次socket注册到selector上，标记为op_read事件，添加事件触发时处理函数socketwrapper
sc.register(getselector(), selectionkey.op_read, socketwrapper);
} catch (exception x) {
log.error(sm.getstring("endpoint.nio.registerfail"), x);
}
} else {
// ？？这里的逻辑，不清楚什么情况下会进入到这个分支里面
final selectionkey key = sc.keyfor(getselector());
if (key == null) {
// the key was cancelled (e.g. due to socket closure)
// and removed from the selector while it was being
// processed. count down the connections at this point
// since it won't have been counted down when the socket
// closed.
socketwrapper.close();
} else {
final niosocketwrapper attachment = (niosocketwrapper) key.attachment();
if (attachment != null) {
// we are registering the key to start with, reset the fairness counter.
try {
int ops = key.interestops() | interestops;
attachment.interestops(ops);
key.interestops(ops);
} catch (cancelledkeyexception ckx) {
cancelledkey(key, socketwrapper);
}
} else {
cancelledkey(key, socketwrapper);
}
}
}
if (running && !paused && eventcache != null) {
pe.reset();
eventcache.push(pe);
}
}
return result;
}
还有一个重要方法就是org.apache.tomcat.util.net.nioendpoint.poller#processkey，上一个方法是获取event，并注册到selector，那这个方法就是通过selector获取到的数据准备好的event，并开始封装成对应的业务处理线程socketprocessorbase，扔到线程池里开始处理
protected void processkey(selectionkey sk, niosocketwrapper socketwrapper) {
try {
if (close) {
cancelledkey(sk, socketwrapper);
} else if (sk.isvalid()) {
if (sk.isreadable() || sk.iswritable()) {
if (socketwrapper.getsendfiledata() != null) {
processsendfile(sk, socketwrapper, false);
} else {
unreg(sk, socketwrapper, sk.readyops());
boolean closesocket = false;
// read goes before write
if (sk.isreadable()) {
//这里如果是异步的操作，就会走这里
if (socketwrapper.readoperation != null) {
if (!socketwrapper.readoperation.process()) {
closesocket = true;
}
} else if (socketwrapper.readblocking) {
// readblocking默认为false
synchronized (socketwrapper.readlock) {
socketwrapper.readblocking = false;
socketwrapper.readlock.notify();
}
} else if (!processsocket(socketwrapper, socketevent.open_read, true)) {
// 处理正常的事件，这里的processsocket就要正式开始处理请求了。
// 将对应的事件封装成对应的线程，然后交给线程池去处理正式的请求业务
closesocket = true;
}
}
if (!closesocket && sk.iswritable()) {
if (socketwrapper.writeoperation != null) {
if (!socketwrapper.writeoperation.process()) {
closesocket = true;
}
} else if (socketwrapper.writeblocking) {
synchronized (socketwrapper.writelock) {
socketwrapper.writeblocking = false;
socketwrapper.writelock.notify();
}
} else if (!processsocket(socketwrapper, socketevent.open_write, true)) {
closesocket = true;
}
}
if (closesocket) {
cancelledkey(sk, socketwrapper);
}
}
}
} else {
// invalid key
cancelledkey(sk, socketwrapper);
}
} catch (cancelledkeyexception ckx) {
cancelledkey(sk, socketwrapper);
} catch (throwable t) {
exceptionutils.handlethrowable(t);
log.error(sm.getstring("endpoint.nio.keyprocessingerror"), t);
}
}
请求具体处理
上一步，selector获取到了就绪的请求socket，然后根据socket注册的触发处理函数等，将这些数据进行封装，扔到了线程池里，开始具体的业务逻辑处理。本节就是从工作线程封装开始，org.apache.tomcat.util.net.socketprocessorbase为工作线程类的抽象类，实现了runnable接口，不同的endpoint实现具体的处理逻辑，本节以nioendpoint为例
以下为org.apache.tomcat.util.net.abstractendpoint#processsocket方法源码
/**
* process the given socketwrapper with the given status. used to trigger
* processing as if the poller (for those endpoints that have one)
* selected the socket.
*
* @param socketwrapper the socket wrapper to process
* @param event the socket event to be processed
* @param dispatch should the processing be performed on a new
* container thread
*
* @return if processing was triggered successfully
*/
public boolean processsocket(socketwrapperbase<s> socketwrapper,
socketevent event, boolean dispatch) {
try {
if (socketwrapper == null) {
return false;
}
// 优先使用已经存在的线程
socketprocessorbase<s> sc = null;
if (processorcache != null) {
sc = processorcache.pop();
}
if (sc == null) {
sc = createsocketprocessor(socketwrapper, event);
} else {
sc.reset(socketwrapper, event);
}
// 获取线程池。线程池的初始化，是在acceptor、poller这两个单独线程启动之前创建
// tomcat使用了自定义的org.apache.tomcat.util.threads.taskqueue，这块tomcat也进行了小的适配开发
// 核心线程为10个，最大200线程
executor executor = getexecutor();
if (dispatch && executor != null) {
executor.execute(sc);
} else {
sc.run();
}
} catch (rejectedexecutionexception ree) {
getlog().warn(sm.getstring("endpoint.executor.fail", socketwrapper) , ree);
return false;
} catch (throwable t) {
exceptionutils.handlethrowable(t);
// this means we got an oom or similar creating a thread, or that
// the pool and its queue are full
getlog().error(sm.getstring("endpoint.process.fail"), t);
return false;
}
return true;
}
上面的方法是得到了处理业务逻辑的线程socketprocessorbase，nioendpoint内部类org.apache.tomcat.util.net.nioendpoint.socketprocessor继承了这个抽象类，也就是具体的业务处理逻辑在org.apache.tomcat.util.net.nioendpoint.socketprocessor#dorun方法中，最终调用到我们的servlet
protected void dorun() {
/*
* do not cache and re-use the value of socketwrapper.getsocket() in
* this method. if the socket closes the value will be updated to
* closed_nio_channel and the previous value potentially re-used for
* a new connection. that can result in a stale cached value which
* in turn can result in unintentionally closing currently active
* connections.
*/
poller poller = nioendpoint.this.poller;
if (poller == null) {
socketwrapper.close();
return;
}
try {
int handshake = -1;
try {
// 握手相关判断逻辑
...
} catch (ioexception x) {
...
}
// 三次握手成功了
if (handshake == 0) {
socketstate state = socketstate.open;
// process the request from this socket
// event为socketevent.open_read，这个变量是org.apache.tomcat.util.net.nioendpoint.poller#processkey方法赋值
if (event == null) {
state = gethandler().process(socketwrapper, socketevent.open_read);
} else {
// 这里就开始正式处理请求了
state = gethandler().process(socketwrapper, event);
}
if (state == socketstate.closed) {
poller.cancelledkey(getselectionkey(), socketwrapper);
}
} else if (handshake == -1 ) {
gethandler().process(socketwrapper, socketevent.connect_fail);
poller.cancelledkey(getselectionkey(), socketwrapper);
} else if (handshake == selectionkey.op_read){
socketwrapper.registerreadinterest();
} else if (handshake == selectionkey.op_write){
socketwrapper.registerwriteinterest();
}
} catch (cancelledkeyexception cx) {
poller.cancelledkey(getselectionkey(), socketwrapper);
} catch (virtualmachineerror vme) {
exceptionutils.handlethrowable(vme);
} catch (throwable t) {
log.error(sm.getstring("endpoint.processing.fail"), t);
poller.cancelledkey(getselectionkey(), socketwrapper);
} finally {
socketwrapper = null;
event = null;
//return to cache
if (running && !paused && processorcache != null) {
processorcache.push(this);
}
}
}
总结
-
tomcat是如何接收网络请求？使用java nio的同步非阻塞去进行网络监听。
org.apache.tomcat.util.net.abstractendpoint#bindwithcleanup中初始化网络监听、ssl{ .... serversock = serversocketchannel.open(); socketproperties.setproperties(serversock.socket()); inetsocketaddress addr = new inetsocketaddress(getaddress(), getportwithoffset()); // 当应用层面的连接数到达最大值时，操作系统可以继续接收连接，那么操作系统能继续接收的最大连接数就是这个队列长度，可以通过acceptcount 参数配置，默认是 100 serversock.bind(addr, getacceptcount()); } serversock.configureblocking(true); //mimic apr behaviororg.apache.tomcat.util.net.nioendpoint#startinternal中初始化业务处理的线程池、连接限制器、poller线程、acceptor线程 -
如何做到高性能的
http协议服务器？tomcat把接收连接、检测 i/o 事件以及处理请求进行了拆分，用不同规模的线程去做对应的事情，这也是tomcat能高并发处理请求的原因。不让线程阻塞，尽量让cpu忙起来
-
是怎么设计的呢？
通过接口、抽象类等，将不同的处理逻辑拆分，各司其职
org.apache.tomcat.util.net.abstractendpoint：i/o事件的检测、处理逻辑都在这个类的实现类里面。使用模板方法，不同的协议有不同的实现方法。nioendpoint/nio2endpoint/aprendpointorg.apache.tomcat.util.net.nioendpoint.poller：引用了java.nio.channels.selector，内部有个事件队列，监听i/o事件具体就是在这里做的org.apache.tomcat.util.net.nioendpoint.niosocketwrapperorg.apache.tomcat.util.net.nioendpoint.socketprocessor: 具体处理请求的线程类
参考：
nioendpoint组件：tomcat如何实现非阻塞i/o？
java nio浅析
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