Tomcat 7 中 NIO 处理分析
Tomcat 的 Connector 有三种运行模式 bio、nio、apr ，先了解一下这三种的区别。java
- bio(blocking I/O)，顾名思义即阻塞式 I/O 操做，表示 Tomcat 使用的是传统的 Java I/O 操做(即
java.io包及其子包)。Tomcat 在默认状况下，就是以 bio 模式运行的。通常而言 bio 模式是三种运行模式中性能最低的一种。 - nio(new I/O)，是 Java SE 1.4 及后续版本提供的一种新的 I/O 操做方式(即
java.nio包及其子包)。Java nio 是一个基于缓冲区并能提供非阻塞 I/O 操做的 Java API ，所以 nio 也被当作是 non-blocking I/O 的缩写。它拥有比传统 I/O 操做( bio )更好的并发运行性能。要让 Tomcat 以 nio 模式来运行只须要在 Tomcat 安装目录/conf/server.xml文件中将 Connector 节点的 protocol 配置成org.apache.coyote.http11.Http11NioProtocol便可。 - apr( Apache Portable Runtime/Apache 可移植运行时)，是 Apache HTTP 服务器的支持库。能够简单地理解为 Tomcat 将以 JNI 的形式调 用Apache HTTP 服务器的核心动态连接库来处理文件读取或网络传输操做，从而大大提升 Tomcat 对静态文件的处理性能。 Tomcat apr 也是在 Tomcat 上运行高并发应用的首选模式。
写个 BIO 的 Socket 服务器仍是比较容易的，无非是每 accept 一个 socket 以后就扔到一个线程中处理请求生成响应，这种方式能够改进的点就是增长线程池的支持，本文主要分析一下 Tomcat 中 NIO 处理方式的相关代码逻辑。算法
关键代码都是在org.apache.tomcat.util.net.NioEndpoint这个类里面，它是 Http11NioProtocol 中负责接收处理 socket 的主要组件，别看代码很长，仔细阅读会发现有不少共通的地方，如：apache
- 都会对JDK中原有的API作一下扩展或者包装，如 ThreadPoolExecutor 是对
java.util.concurrent.ThreadPoolExecutor的扩展，NioChannel 是对 ByteChannel 的扩展，KeyAttachment 则是对 NioChannel 的包装 - 不少类设计成非 GC 的，方便缓存和重复使用，实现方式都是经过 ConcurrentLinkedQueue 类构造一个队列。好比 NioEndpoint 类里面的 ConcurrentLinkedQueue processorCache、ConcurrentLinkedQueue keyCache、ConcurrentLinkedQueue eventCache、ConcurrentLinkedQueue nioChannels 。Poller 类里面的 ConcurrentLinkedQueue events
先看下整个 Connector 组件结构图： windows
看过以前 Tomcat 启动文章的应该都知道，Connector 的启动会调用 Connector 类的 startInternal 方法，里面调用了 protocolHandler 的 start() ，该方法中将调用抽象的 endpoint 的 start() 方法，这个方法会调用到具体 Endpoint 类的 startInternal() ，因此代码分析先从 NioEndpoint 类的 startInternal 看起。数组
1.NioEndpoint 类核心组件的初始化
/**
* Start the NIO endpoint, creating acceptor, poller threads.
*/
@Override
public void startInternal() throws Exception {
if (!running) {
running = true;
paused = false;
// Create worker collection
if ( getExecutor() == null ) {
// 构造线程池，用于后续执行SocketProcessor线程，这就是上图中的Worker。
createExecutor();
}
initializeConnectionLatch();
// Start poller threads
// 根据处理器数量构造必定数目的轮询器，即上图中的Poller
pollers = new Poller[getPollerThreadCount()];
for (int i=0; i<pollers.length; i++) {
pollers[i] = new Poller();
Thread pollerThread = new Thread(pollers[i], getName() + "-ClientPoller-"+i);
pollerThread.setPriority(threadPriority);
pollerThread.setDaemon(true);
pollerThread.start();
}
// 建立接收者线程，即上图中的Acceptor
startAcceptorThreads();
}
}
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startAcceptorThreads 调用的是父类org.apache.tomcat.util.net.AbstractEndpoint中的实现：缓存
protected final void startAcceptorThreads() {
int count = getAcceptorThreadCount();
acceptors = new Acceptor[count];
for (int i = 0; i < count; i++) {
// 调用子类的createAcceptor方法，本例中即NioEndpoint类的createAcceptor方法
acceptors[i] = createAcceptor();
String threadName = getName() + "-Acceptor-" + i;
acceptors[i].setThreadName(threadName);
Thread t = new Thread(acceptors[i], threadName);
t.setPriority(getAcceptorThreadPriority());
t.setDaemon(getDaemon());
t.start();
}
}
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以上就是 Acceptor、Poller、Worker 等核心组件的初始化过程。tomcat
2.请求接收
核心组件初始化以后接着就是 Acceptor 线程接收 socket 链接，看下 Acceptor 的源码：bash
// --------------------------------------------------- Acceptor Inner Class
/**
* 后台线程，用于监听TCP/IP链接以及将它们分发给相应的调度器处理。
* The background thread that listens for incoming TCP/IP connections and
* hands them off to an appropriate processor.
*/
protected class Acceptor extends AbstractEndpoint.Acceptor {
@Override
public void run() {
int errorDelay = 0;
// 循环遍历直到接收到关闭命令
// Loop until we receive a shutdown command
while (running) {
// Loop if endpoint is paused
while (paused && running) {
state = AcceptorState.PAUSED;
try {
Thread.sleep(50);
} catch (InterruptedException e) {
// Ignore
}
}
if (!running) {
break;
}
state = AcceptorState.RUNNING;
try {
// 若是已经达到最大链接数则让线程等待
//if we have reached max connections, wait
countUpOrAwaitConnection();
SocketChannel socket = null;
try {
// 接收链接，这里用的阻塞模式。
// Accept the next incoming connection from the server
// socket
socket = serverSock.accept();
} catch (IOException ioe) {
//we didn't get a socket
countDownConnection();
// Introduce delay if necessary
errorDelay = handleExceptionWithDelay(errorDelay);
// re-throw
throw ioe;
}
// Successful accept, reset the error delay
errorDelay = 0;
// 注意这个setSocketOptions方法
// 它将把上面接收到的socket添加到轮询器Poller中
// setSocketOptions() will add channel to the poller
// if successful
if (running && !paused) {
if (!setSocketOptions(socket)) {
countDownConnection();
closeSocket(socket);
}
} else {
countDownConnection();
closeSocket(socket);
}
} catch (SocketTimeoutException sx) {
// Ignore: Normal condition
} catch (IOException x) {
if (running) {
log.error(sm.getString("endpoint.accept.fail"), x);
}
} catch (OutOfMemoryError oom) {
try {
oomParachuteData = null;
releaseCaches();
log.error("", oom);
}catch ( Throwable oomt ) {
try {
try {
System.err.println(oomParachuteMsg);
oomt.printStackTrace();
}catch (Throwable letsHopeWeDontGetHere){
ExceptionUtils.handleThrowable(letsHopeWeDontGetHere);
}
}catch (Throwable letsHopeWeDontGetHere){
ExceptionUtils.handleThrowable(letsHopeWeDontGetHere);
}
}
} catch (Throwable t) {
ExceptionUtils.handleThrowable(t);
log.error(sm.getString("endpoint.accept.fail"), t);
}
}
state = AcceptorState.ENDED;
}
}
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3.Socket 参数设置
在 Acceptor 里接收到一个链接以后调用 setSocketOptions 方法设置 SocketChannel 的一些参数，而后将 SocketChannel 注册到 Poller 中。看下 setSocketOptions 的实现：服务器
/**
* Process the specified connection.
*/
protected boolean setSocketOptions(SocketChannel socket) {
// Process the connection
try {
// 将SocketChannel配置为非阻塞模式
//disable blocking, APR style, we are gonna be polling it
socket.configureBlocking(false);
Socket sock = socket.socket();
// 设置Socket参数值（从server.xml的Connector节点上获取参数值）
// 好比Socket发送、接收的缓存大小、心跳检测等
socketProperties.setProperties(sock);
// 从NioChannel的缓存队列中取出一个NioChannel
// NioChannel是SocketChannel的一个的包装类
// 这里对上层屏蔽SSL和通常TCP链接的差别
NioChannel channel = nioChannels.poll();
// 缓存队列中没有则新建一个NioChannel
if ( channel == null ) {
// SSL setup
if (sslContext != null) {
SSLEngine engine = createSSLEngine();
int appbufsize = engine.getSession().getApplicationBufferSize();
NioBufferHandler bufhandler = new NioBufferHandler(Math.max(appbufsize,socketProperties.getAppReadBufSize()),
Math.max(appbufsize,socketProperties.getAppWriteBufSize()),
socketProperties.getDirectBuffer());
channel = new SecureNioChannel(socket, engine, bufhandler, selectorPool);
} else {
// normal tcp setup
NioBufferHandler bufhandler = new NioBufferHandler(socketProperties.getAppReadBufSize(),
socketProperties.getAppWriteBufSize(),
socketProperties.getDirectBuffer());
channel = new NioChannel(socket, bufhandler);
}
} else {
// 将SocketChannel关联到从缓存队列中获取的NioChannel上来
channel.setIOChannel(socket);
if ( channel instanceof SecureNioChannel ) {
SSLEngine engine = createSSLEngine();
((SecureNioChannel)channel).reset(engine);
} else {
channel.reset();
}
}
// 将新接收到的SocketChannel注册到Poller中
getPoller0().register(channel);
} catch (Throwable t) {
ExceptionUtils.handleThrowable(t);
try {
log.error("",t);
} catch (Throwable tt) {
ExceptionUtils.handleThrowable(t);
}
// Tell to close the socket
return false;
}
return true;
}
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核心调用是最后的getPoller0().register(channel);它将配置好的 SocketChannel 包装成一个 PollerEvent ，而后加入到 Poller 的 events 缓存队列中。网络
4.读取事件注册
getPoller0 方法将轮询当前的 Poller 数组，从中取出一个 Poller 返回。（ Poller 的初始化参见上述第1步：NioEndpoint 类核心组件的初始化）
/**
* Return an available poller in true round robin fashion
*/
public Poller getPoller0() {
// 最简单的轮询调度算法，poller的计数器不断加1再对poller数组取余数
int idx = Math.abs(pollerRotater.incrementAndGet()) % pollers.length;
return pollers[idx];
}
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以后调用 Poller 对象的 register 方法：
public void register(final NioChannel socket) {
// 设置socket的Poller引用，便于后续处理
socket.setPoller(this);
// 从NioEndpoint的keyCache缓存队列中取出一个KeyAttachment
KeyAttachment key = keyCache.poll();
// KeyAttachment实际是NioChannel的包装类
final KeyAttachment ka = key!=null?key:new KeyAttachment(socket);
// 重置KeyAttachment对象中Poller、NioChannel等成员变量的引用
ka.reset(this,socket,getSocketProperties().getSoTimeout());
ka.setKeepAliveLeft(NioEndpoint.this.getMaxKeepAliveRequests());
ka.setSecure(isSSLEnabled());
// 从Poller的事件对象缓存中取出一个PollerEvent，并用socket初始化事件对象
PollerEvent r = eventCache.poll();
// 设置读操做为感兴趣的操做
ka.interestOps(SelectionKey.OP_READ);//this is what OP_REGISTER turns into.
if ( r==null) r = new PollerEvent(socket,ka,OP_REGISTER);
else r.reset(socket,ka,OP_REGISTER);
// 加入到Poller对象里的事件队列
addEvent(r);
}
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看下 Poller 类里 addEvent 的代码：
/**
* Only used in this class. Will be made private in Tomcat 8.0.x
* @deprecated
*/
@Deprecated
public void addEvent(Runnable event) {
events.offer(event);
if ( wakeupCounter.incrementAndGet() == 0 ) selector.wakeup();
}
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就两行，第一行从 event 对象添加到缓存队列中，第二行若是当前事件队列中没有事件，则唤醒处于阻塞状态的 selector 。
5.Poller 处理流程
上面讲的是从 Acceptor 中接收到的 Socket 以 PollerEvent 的形式包装并添加到 Poller 的事件缓存队列中，接下来看看另一个核心组件 Poller 的处理过程：
/**
* Poller class.
*/
public class Poller implements Runnable {
// 这就是NIO中用到的选择器，能够看出每个Poller都会关联一个Selector
protected Selector selector;
// 待处理的事件队列
protected ConcurrentLinkedQueue events = new ConcurrentLinkedQueue();
// 唤醒多路复用器的条件阈值
protected AtomicLong wakeupCounter = new AtomicLong(0l);
public Poller() throws IOException {
// 对Selector的同步访问，经过调用Selector.open()方法建立一个Selector
synchronized (Selector.class) {
// Selector.open() isn't thread safe
// http://bugs.sun.com/view_bug.do?bug_id=6427854
// Affects 1.6.0_29, fixed in 1.7.0_01
this.selector = Selector.open();
}
}
// 经过addEvent方法将事件添加到Poller的事件队列中
/**
* Only used in this class. Will be made private in Tomcat 8.0.x
* @deprecated
*/
@Deprecated
public void addEvent(Runnable event) {
events.offer(event);
// 若是队列中没有待处理的事件则唤醒处于阻塞状态的selector
if ( wakeupCounter.incrementAndGet() == 0 ) selector.wakeup();
}
// 处理事件队列中的全部事件，若是事件队列是空的则返回false
/**
* Processes events in the event queue of the Poller.
*
* @return true复制代码 if some events were processed,
* false复制代码 if queue was empty
*/
public boolean events() {
boolean result = false;
Runnable r = null;
// 将Poller的事件队列中的事件逐个取出并执行相应的事件线程
while ( (r = events.poll()) != null ) {
result = true;
try {
// 执行事件处理逻辑
// 这里将事件设计成线程是将具体的事件处理逻辑和事件框架分开
r.run();
if ( r instanceof PollerEvent ) {
((PollerEvent)r).reset();
// 事件处理完以后，将事件对象返回NIOEndpoint的事件对象缓存中
eventCache.offer((PollerEvent)r);
}
} catch ( Throwable x ) {
log.error("",x);
}
}
return result;
}
// 将socket包装成统一的事件对象PollerEvent，加入到待处理事件队列中
public void register(final NioChannel socket) {
socket.setPoller(this);
KeyAttachment key = keyCache.poll();
final KeyAttachment ka = key!=null?key:new KeyAttachment(socket);
ka.reset(this,socket,getSocketProperties().getSoTimeout());
ka.setKeepAliveLeft(NioEndpoint.this.getMaxKeepAliveRequests());
ka.setSecure(isSSLEnabled());
// 从NIOEndpoint的事件对象缓存中取出一个事件对象
PollerEvent r = eventCache.poll();
ka.interestOps(SelectionKey.OP_READ);//this is what OP_REGISTER turns into.
if ( r==null) r = new PollerEvent(socket,ka,OP_REGISTER);
else r.reset(socket,ka,OP_REGISTER);
// 将事件添加打Poller的事件队列中
addEvent(r);
}
// Poller是一个线程，该线程同Acceptor同样会监听TCP/IP链接并将它们交给合适的处理器处理
/**
* The background thread that listens for incoming TCP/IP connections and
* hands them off to an appropriate processor.
*/
@Override
public void run() {
// Loop until destroy() is called
while (true) {
try {
// Loop if endpoint is paused
while (paused && (!close) ) {
try {
Thread.sleep(100);
} catch (InterruptedException e) {
// Ignore
}
}
boolean hasEvents = false;
// Time to terminate?
if (close) {
events();
timeout(0, false);
try {
selector.close();
} catch (IOException ioe) {
log.error(sm.getString(
"endpoint.nio.selectorCloseFail"), ioe);
}
break;
} else {
// 执行事件队列中的事件线程
hasEvents = events();
}
try {
if ( !close ) {
if (wakeupCounter.getAndSet(-1) > 0) {
// 把wakeupCounter设成-1，这是与addEvent里的代码呼应，这样会唤醒selector
//if we are here, means we have other stuff to do
//do a non blocking select
// 以非阻塞方式查看selector是否有事件发生
keyCount = selector.selectNow();
} else {
// 查看selector是否有事件发生，超过指定时间则当即返回
keyCount = selector.select(selectorTimeout);
}
wakeupCounter.set(0);
}
if (close) {
// 执行事件队列中的事件线程
events();
timeout(0, false);
try {
selector.close();
} catch (IOException ioe) {
log.error(sm.getString(
"endpoint.nio.selectorCloseFail"), ioe);
}
break;
}
} catch ( NullPointerException x ) {
//sun bug 5076772 on windows JDK 1.5
if ( log.isDebugEnabled() ) log.debug("Possibly encountered sun bug 5076772 on windows JDK 1.5",x);
if ( wakeupCounter == null || selector == null ) throw x;
continue;
} catch ( CancelledKeyException x ) {
//sun bug 5076772 on windows JDK 1.5
if ( log.isDebugEnabled() ) log.debug("Possibly encountered sun bug 5076772 on windows JDK 1.5",x);
if ( wakeupCounter == null || selector == null ) throw x;
continue;
} catch (Throwable x) {
ExceptionUtils.handleThrowable(x);
log.error("",x);
continue;
}
//either we timed out or we woke up, process events first
if ( keyCount == 0 ) hasEvents = (hasEvents | events());
Iterator iterator =
keyCount > 0 ? selector.selectedKeys().iterator() : null;
// 根据向selector中注册的key遍历channel中已经就绪的keys，并处理这些key
// Walk through the collection of ready keys and dispatch
// any active event.
while (iterator != null && iterator.hasNext()) {
SelectionKey sk = iterator.next();
// 这里的attachment方法返回的就是在register()方法中注册的
// 而KeyAttachment对象是对socket的包装
KeyAttachment attachment = (KeyAttachment)sk.attachment();
// Attachment may be null if another thread has called
// cancelledKey()
if (attachment == null) {
iterator.remove();
} else {
// 更新通道最近一次发生事件的时间
// 防止因超时没有事件发生而被剔除出selector
attachment.access();
iterator.remove();
// 具体处理通道的逻辑
processKey(sk, attachment);
}
}//while
//process timeouts
// 多路复用器每执行一遍完整的轮询便查看全部通道是否超时
// 对超时的通道将会被剔除出多路复用器
timeout(keyCount,hasEvents);
if ( oomParachute > 0 && oomParachuteData == null ) checkParachute();
} catch (OutOfMemoryError oom) {
try {
oomParachuteData = null;
releaseCaches();
log.error("", oom);
}catch ( Throwable oomt ) {
try {
System.err.println(oomParachuteMsg);
oomt.printStackTrace();
}catch (Throwable letsHopeWeDontGetHere){
ExceptionUtils.handleThrowable(letsHopeWeDontGetHere);
}
}
}
}//while
synchronized (this) {
this.notifyAll();
}
stopLatch.countDown();
}
// 处理selector检测到的通道事件
protected boolean processKey(SelectionKey sk, KeyAttachment attachment) {
boolean result = true;
try {
if ( close ) {
cancelledKey(sk, SocketStatus.STOP, attachment.comet);
} else if ( sk.isValid() && attachment != null ) {
// 确保通道不会因超时而被剔除
attachment.access();//make sure we don't time out valid sockets
sk.attach(attachment);//cant remember why this is here
NioChannel channel = attachment.getChannel();
// 处理通道发生的读写事件
if (sk.isReadable() || sk.isWritable() ) {
if ( attachment.getSendfileData() != null ) {
processSendfile(sk,attachment, false);
} else {
if ( isWorkerAvailable() ) {
// 在通道上注销对已经发生事件的关注
unreg(sk, attachment, sk.readyOps());
boolean closeSocket = false;
// Read goes before write
if (sk.isReadable()) {
// 具体的通道处理逻辑
if (!processSocket(channel, SocketStatus.OPEN_READ, true)) {
closeSocket = true;
}
}
if (!closeSocket && sk.isWritable()) {
if (!processSocket(channel, SocketStatus.OPEN_WRITE, true)) {
closeSocket = true;
}
}
if (closeSocket) {
// 解除无效通道
cancelledKey(sk,SocketStatus.DISCONNECT,false);
}
} else {
result = false;
}
}
}
} else {
//invalid key
cancelledKey(sk, SocketStatus.ERROR,false);
}
} catch ( CancelledKeyException ckx ) {
cancelledKey(sk, SocketStatus.ERROR,false);
} catch (Throwable t) {
ExceptionUtils.handleThrowable(t);
log.error("",t);
}
return result;
}
// 这个unreg()很巧妙，防止了通道对同一个事件不断select的问题
protected void unreg(SelectionKey sk, KeyAttachment attachment, int readyOps) {
//this is a must, so that we don't have multiple threads messing with the socket
reg(sk,attachment,sk.interestOps()& (~readyOps));
}
// 向NioChannel注册感兴趣的事件，具体代码看下面的PollerEvent类的说明
protected void reg(SelectionKey sk, KeyAttachment attachment, int intops) {
sk.interestOps(intops);
attachment.interestOps(intops);
attachment.setCometOps(intops);
}
}
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6.PollerEvent 处理流程
Poller 处理的核心是启动执行事件队列中的 PollerEvent，接着从 selector 中遍历已经就绪的 key ，一旦发生了感兴趣的事件，则交由 processSocket 方法处理。PollerEvent 的做用是向 socket 注册或更新感兴趣的事件：
/**
*
* PollerEvent, cacheable object for poller events to avoid GC
*/
public static class PollerEvent implements Runnable {
// 每一个PollerEvent都会保存NioChannel的引用
protected NioChannel socket;
protected int interestOps;
protected KeyAttachment key;
public PollerEvent(NioChannel ch, KeyAttachment k, int intOps) {
reset(ch, k, intOps);
}
public void reset(NioChannel ch, KeyAttachment k, int intOps) {
socket = ch;
interestOps = intOps;
key = k;
}
public void reset() {
reset(null, null, 0);
}
@Override
public void run() {
//socket第一次注册到selector中，完成对socket读事件的注册
if ( interestOps == OP_REGISTER ) {
try {
socket.getIOChannel().register(socket.getPoller().getSelector(), SelectionKey.OP_READ, key);
} catch (Exception x) {
log.error("", x);
}
} else {
// socket以前已经注册到了selector中，更新socket所感兴趣的事件
final SelectionKey key = socket.getIOChannel().keyFor(socket.getPoller().getSelector());
try {
boolean cancel = false;
if (key != null) {
final KeyAttachment att = (KeyAttachment) key.attachment();
if ( att!=null ) {
//handle callback flag
if (att.isComet() && (interestOps & OP_CALLBACK) == OP_CALLBACK ) {
att.setCometNotify(true);
} else {
att.setCometNotify(false);
}
interestOps = (interestOps & (~OP_CALLBACK));//remove the callback flag
// 刷新事件的最后访问时间，防止事件超时
att.access();//to prevent timeout
//we are registering the key to start with, reset the fairness counter.
int ops = key.interestOps() | interestOps;
att.interestOps(ops);
key.interestOps(ops);
} else {
cancel = true;
}
} else {
cancel = true;
}
if ( cancel ) socket.getPoller().cancelledKey(key,SocketStatus.ERROR,false);
}catch (CancelledKeyException ckx) {
try {
socket.getPoller().cancelledKey(key,SocketStatus.DISCONNECT,true);
}catch (Exception ignore) {}
}
}//end if
}//run
@Override
public String toString() {
return super.toString()+"[intOps="+this.interestOps+"]";
}
}
复制代码
7.将 socket 交给 Worker 执行
在第5步的 Poller 处理流程的分析中看到它的 run 方法最后会调用 processKey() 处理 selector 检测到的通道事件，而在这个方法最后会调用 processSocket 来调用具体的通道处理逻辑，看下 processSocket 方法的实现：
public boolean processSocket(NioChannel socket, SocketStatus status, boolean dispatch) {
try {
KeyAttachment attachment = (KeyAttachment)socket.getAttachment();
if (attachment == null) {
return false;
}
attachment.setCometNotify(false); //will get reset upon next reg
// 从SocketProcessor的缓存队列中取出一个来处理socket
SocketProcessor sc = processorCache.poll();
if ( sc == null ) sc = new SocketProcessor(socket,status);
else sc.reset(socket,status);
// 将有事件发生的socket交给Worker处理
if ( dispatch && getExecutor()!=null ) getExecutor().execute(sc);
else sc.run();
} catch (RejectedExecutionException rx) {
log.warn("Socket processing request was rejected for:"+socket,rx);
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
log.error(sm.getString("endpoint.process.fail"), t);
return false;
}
return true;
}
复制代码
Poller 经过 NioEndpoint 的协调，将发生事件的 socket 交给工做者线程 Worker 来进一步处理。整个事件框架的工做就到此结束，下面就是 Worker 的处理。
8.从 socket 中处理请求
在 Tomcat 6 版本的 NIO 处理实现中有一个 Worker 类，在 Tomcat 7 中把它去掉了，但工做者的职责还在，只是交由了上面看到的 SocketProcessor 这个类来担当，看下这个类的实现代码：
// ---------------------------------------------- SocketProcessor Inner Class
// 这个类至关于一个工做者，但只会在一个外部线程池中简单使用。
/**
* This class is the equivalent of the Worker, but will simply use in an
* external Executor thread pool.
*/
protected class SocketProcessor implements Runnable {
// 每一个SocketProcessor保存一个NioChannel的引用
protected NioChannel socket = null;
protected SocketStatus status = null;
public SocketProcessor(NioChannel socket, SocketStatus status) {
reset(socket,status);
}
public void reset(NioChannel socket, SocketStatus status) {
this.socket = socket;
this.status = status;
}
@Override
public void run() {
// 从socket中获取SelectionKey
SelectionKey key = socket.getIOChannel().keyFor(
socket.getPoller().getSelector());
KeyAttachment ka = null;
if (key != null) {
ka = (KeyAttachment)key.attachment();
}
// Upgraded connections need to allow multiple threads to access the
// connection at the same time to enable blocking IO to be used when
// NIO has been configured
if (ka != null && ka.isUpgraded() &&
SocketStatus.OPEN_WRITE == status) {
synchronized (ka.getWriteThreadLock()) {
doRun(key, ka);
}
} else {
synchronized (socket) {
doRun(key, ka);
}
}
}
private void doRun(SelectionKey key, KeyAttachment ka) {
try {
int handshake = -1;
try {
if (key != null) {
// For STOP there is no point trying to handshake as the
// Poller has been stopped.
if (socket.isHandshakeComplete() ||
status == SocketStatus.STOP) {
handshake = 0;
} else {
handshake = socket.handshake(
key.isReadable(), key.isWritable());
// The handshake process reads/writes from/to the
// socket. status may therefore be OPEN_WRITE once
// the handshake completes. However, the handshake
// happens when the socket is opened so the status
// must always be OPEN_READ after it completes. It
// is OK to always set this as it is only used if
// the handshake completes.
status = SocketStatus.OPEN_READ;
}
}
}catch ( IOException x ) {
handshake = -1;
if ( log.isDebugEnabled() ) log.debug("Error during SSL handshake",x);
}catch ( CancelledKeyException ckx ) {
handshake = -1;
}
if ( handshake == 0 ) {
SocketState state = SocketState.OPEN;
// Process the request from this socket
if (status == null) {
// 最关键的代码，这里将KeyAttachment(实际就是socket)交给Handler处理请求
state = handler.process(ka, SocketStatus.OPEN_READ);
} else {
state = handler.process(ka, status);
}
if (state == SocketState.CLOSED) {
// Close socket and pool
try {
close(ka, socket, key, SocketStatus.ERROR);
} catch ( Exception x ) {
log.error("",x);
}
}
} else if (handshake == -1 ) {
close(ka, socket, key, SocketStatus.DISCONNECT);
} else {
ka.getPoller().add(socket, handshake);
}
} catch (CancelledKeyException cx) {
socket.getPoller().cancelledKey(key, null, false);
} catch (OutOfMemoryError oom) {
try {
oomParachuteData = null;
log.error("", oom);
if (socket != null) {
socket.getPoller().cancelledKey(key,SocketStatus.ERROR, false);
}
releaseCaches();
}catch ( Throwable oomt ) {
try {
System.err.println(oomParachuteMsg);
oomt.printStackTrace();
}catch (Throwable letsHopeWeDontGetHere){
ExceptionUtils.handleThrowable(letsHopeWeDontGetHere);
}
}
} catch (VirtualMachineError vme) {
ExceptionUtils.handleThrowable(vme);
}catch ( Throwable t ) {
log.error("",t);
if (socket != null) {
socket.getPoller().cancelledKey(key,SocketStatus.ERROR,false);
}
} finally {
socket = null;
status = null;
//return to cache
if (running && !paused) {
processorCache.offer(this);
}
}
}
private void close(KeyAttachment ka, NioChannel socket, SelectionKey key,
SocketStatus socketStatus) {
...
}
}
复制代码
能够看到由 SocketProcessor 寻找合适的 Handler 处理器作最终 socket 转换处理。
能够用下面这幅图总结一下 NioEndpoint 的主要流程：
Acceptor 和 Poller 是线程数组，Worker 是一个线程池（ Executor ）
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