Tomcat 的 Connector 有三種執行模式 bio、nio、apr ，先了解一下這三種的區別。
- bio(blocking I/O)，顧名思義即阻塞式 I/O 操作，表示 Tomcat 使用的是傳統的 Java I/O 操作(即
java.io包及其子包)。Tomcat 在預設情況下，就是以 bio 模式執行的。一般而言 bio 模式是三種執行模式中效能最低的一種。 - nio(new I/O)，是 Java SE 1.4 及後續版本提供的一種新的 I/O 操作方式(即
java.nio包及其子包)。Java nio 是一個基於緩衝區並能提供非阻塞 I/O 操作的 Java API ，因此 nio 也被看成是 non-blocking I/O 的縮寫。它擁有比傳統 I/O 操作( bio )更好的併發執行效能。要讓 Tomcat 以 nio 模式來執行只需要在 Tomcat 安裝目錄/conf/server.xml檔案中將 Connector 節點的 protocol 配置成org.apache.coyote.http11.Http11NioProtocol即可。 - apr( Apache Portable Runtime/Apache 可移植執行時)，是 Apache HTTP 伺服器的支援庫。可以簡單地理解為 Tomcat 將以 JNI 的形式調 用Apache HTTP 伺服器的核心動態連結庫來處理檔案讀取或網路傳輸操作，從而大大提高 Tomcat 對靜態檔案的處理效能。 Tomcat apr 也是在 Tomcat 上執行高併發應用的首選模式。
寫個 BIO 的 Socket 伺服器還是比較容易的，無非是每 accept 一個 socket 之後就扔到一個執行緒中處理請求生成響應，這種方式可以改進的點就是增加執行緒池的支援，本文主要分析一下 Tomcat 中 NIO 處理方式的相關程式碼邏輯。
關鍵程式碼都是在org.apache.tomcat.util.net.NioEndpoint這個類裡面，它是 Http11NioProtocol 中負責接收處理 socket 的主要元件，別看程式碼很長，仔細閱讀會發現有很多共通的地方，如：
- 都會對JDK中原有的API做一下擴充套件或者包裝，如 ThreadPoolExecutor 是對
java.util.concurrent.ThreadPoolExecutor的擴充套件，NioChannel 是對 ByteChannel 的擴充套件，KeyAttachment 則是對 NioChannel 的包裝 - 很多類設計成非 GC 的，方便快取和重複使用，實現方式都是通過 ConcurrentLinkedQueue 類構造一個佇列。比如 NioEndpoint 類裡面的 ConcurrentLinkedQueue processorCache、ConcurrentLinkedQueue keyCache、ConcurrentLinkedQueue eventCache、ConcurrentLinkedQueue nioChannels 。Poller 類裡面的 ConcurrentLinkedQueue events
先看下整個 Connector 元件結構圖：
看過之前 Tomcat 啟動文章的應該都知道，Connector 的啟動會呼叫 Connector 類的 startInternal 方法，裡面呼叫了 protocolHandler 的 start() ，該方法中將呼叫抽象的 endpoint 的 start() 方法，這個方法會呼叫到具體 Endpoint 類的 startInternal() ，所以程式碼分析先從 NioEndpoint 類的 startInternal 看起。
1.NioEndpoint 類核心元件的初始化
/**
* 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 ) {
// 構造執行緒池，用於後續執行SocketProcessor執行緒，這就是上圖中的Worker。
createExecutor();
}
initializeConnectionLatch();
// Start poller threads
// 根據處理器數量構造一定數目的輪詢器，即上圖中的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();
}
// 建立接收者執行緒，即上圖中的Acceptor
startAcceptorThreads();
}
}
複製程式碼startAcceptorThreads 呼叫的是父類org.apache.tomcat.util.net.AbstractEndpoint中的實現：
protected final void startAcceptorThreads() {
int count = getAcceptorThreadCount();
acceptors = new Acceptor[count];
for (int i = 0; i < count; i++) {
// 呼叫子類的createAcceptor方法，本例中即NioEndpoint類的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();
}
}
複製程式碼以上就是 Acceptor、Poller、Worker 等核心元件的初始化過程。
2.請求接收
核心元件初始化之後接著就是 Acceptor 執行緒接收 socket 連線，看下 Acceptor 的原始碼：
// --------------------------------------------------- Acceptor Inner Class
/**
* 後臺執行緒，用於監聽TCP/IP連線以及將它們分發給相應的排程器處理。
* 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;
// 迴圈遍歷直到接收到關閉命令
// 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 {
// 如果已經達到最大連線數則讓執行緒等待
//if we have reached max connections, wait
countUpOrAwaitConnection();
SocketChannel socket = null;
try {
// 接收連線，這裡用的阻塞模式。
// 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;
// 注意這個setSocketOptions方法
// 它將把上面接收到的socket新增到輪詢器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;
}
}
複製程式碼3.Socket 引數設定
在 Acceptor 裡接收到一個連線之後呼叫 setSocketOptions 方法設定 SocketChannel 的一些引數，然後將 SocketChannel 註冊到 Poller 中。看下 setSocketOptions 的實現：
/**
* Process the specified connection.
*/
protected boolean setSocketOptions(SocketChannel socket) {
// Process the connection
try {
// 將SocketChannel配置為非阻塞模式
//disable blocking, APR style, we are gonna be polling it
socket.configureBlocking(false);
Socket sock = socket.socket();
// 設定Socket引數值（從server.xml的Connector節點上獲取引數值）
// 比如Socket傳送、接收的快取大小、心跳檢測等
socketProperties.setProperties(sock);
// 從NioChannel的快取佇列中取出一個NioChannel
// NioChannel是SocketChannel的一個的包裝類
// 這裡對上層遮蔽SSL和一般TCP連線的差異
NioChannel channel = nioChannels.poll();
// 快取佇列中沒有則新建一個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 {
// 將SocketChannel關聯到從快取佇列中獲取的NioChannel上來
channel.setIOChannel(socket);
if ( channel instanceof SecureNioChannel ) {
SSLEngine engine = createSSLEngine();
((SecureNioChannel)channel).reset(engine);
} else {
channel.reset();
}
}
// 將新接收到的SocketChannel註冊到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;
}
複製程式碼核心呼叫是最後的getPoller0().register(channel);它將配置好的 SocketChannel 包裝成一個 PollerEvent ，然後加入到 Poller 的 events 快取佇列中。
4.讀取事件註冊
getPoller0 方法將輪詢當前的 Poller 陣列，從中取出一個 Poller 返回。（ Poller 的初始化參見上述第1步：NioEndpoint 類核心元件的初始化）
/**
* Return an available poller in true round robin fashion
*/
public Poller getPoller0() {
// 最簡單的輪詢排程演算法，poller的計數器不斷加1再對poller陣列取餘數
int idx = Math.abs(pollerRotater.incrementAndGet()) % pollers.length;
return pollers[idx];
}
複製程式碼之後呼叫 Poller 物件的 register 方法：
public void register(final NioChannel socket) {
// 設定socket的Poller引用，便於後續處理
socket.setPoller(this);
// 從NioEndpoint的keyCache快取佇列中取出一個KeyAttachment
KeyAttachment key = keyCache.poll();
// KeyAttachment實際是NioChannel的包裝類
final KeyAttachment ka = key!=null?key:new KeyAttachment(socket);
// 重置KeyAttachment物件中Poller、NioChannel等成員變數的引用
ka.reset(this,socket,getSocketProperties().getSoTimeout());
ka.setKeepAliveLeft(NioEndpoint.this.getMaxKeepAliveRequests());
ka.setSecure(isSSLEnabled());
// 從Poller的事件物件快取中取出一個PollerEvent，並用socket初始化事件物件
PollerEvent r = eventCache.poll();
// 設定讀操作為感興趣的操作
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物件裡的事件佇列
addEvent(r);
}
複製程式碼看下 Poller 類裡 addEvent 的程式碼：
/**
* 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();
}
複製程式碼就兩行，第一行從 event 物件新增到快取佇列中，第二行如果當前事件佇列中沒有事件，則喚醒處於阻塞狀態的 selector 。
5.Poller 處理流程
上面講的是從 Acceptor 中接收到的 Socket 以 PollerEvent 的形式包裝並新增到 Poller 的事件快取佇列中，接下來看看另外一個核心元件 Poller 的處理過程：
/**
* Poller class.
*/
public class Poller implements Runnable {
// 這就是NIO中用到的選擇器，可以看出每一個Poller都會關聯一個Selector
protected Selector selector;
// 待處理的事件佇列
protected ConcurrentLinkedQueue events = new ConcurrentLinkedQueue();
// 喚醒多路複用器的條件閾值
protected AtomicLong wakeupCounter = new AtomicLong(0l);
public Poller() throws IOException {
// 對Selector的同步訪問，通過呼叫Selector.open()方法建立一個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();
}
}
// 通過addEvent方法將事件新增到Poller的事件佇列中
/**
* Only used in this class. Will be made private in Tomcat 8.0.x
* @deprecated
*/
@Deprecated
public void addEvent(Runnable event) {
events.offer(event);
// 如果佇列中沒有待處理的事件則喚醒處於阻塞狀態的selector
if ( wakeupCounter.incrementAndGet() == 0 ) selector.wakeup();
}
// 處理事件佇列中的所有事件，如果事件佇列是空的則返回false
/**
* Processes events in the event queue of the Poller.
*
* @return true複製程式碼 if some events were processed,
* false複製程式碼 if queue was empty
*/
public boolean events() {
boolean result = false;
Runnable r = null;
// 將Poller的事件佇列中的事件逐個取出並執行相應的事件執行緒
while ( (r = events.poll()) != null ) {
result = true;
try {
// 執行事件處理邏輯
// 這裡將事件設計成執行緒是將具體的事件處理邏輯和事件框架分開
r.run();
if ( r instanceof PollerEvent ) {
((PollerEvent)r).reset();
// 事件處理完之後，將事件物件返回NIOEndpoint的事件物件快取中
eventCache.offer((PollerEvent)r);
}
} catch ( Throwable x ) {
log.error("",x);
}
}
return result;
}
// 將socket包裝成統一的事件物件PollerEvent，加入到待處理事件佇列中
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());
// 從NIOEndpoint的事件物件快取中取出一個事件物件
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);
// 將事件新增打Poller的事件佇列中
addEvent(r);
}
// Poller是一個執行緒，該執行緒同Acceptor一樣會監聽TCP/IP連線並將它們交給合適的處理器處理
/**
* 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 {
// 執行事件佇列中的事件執行緒
hasEvents = events();
}
try {
if ( !close ) {
if (wakeupCounter.getAndSet(-1) > 0) {
// 把wakeupCounter設成-1，這是與addEvent裡的程式碼呼應，這樣會喚醒selector
//if we are here, means we have other stuff to do
//do a non blocking select
// 以非阻塞方式檢視selector是否有事件發生
keyCount = selector.selectNow();
} else {
// 檢視selector是否有事件發生，超過指定時間則立即返回
keyCount = selector.select(selectorTimeout);
}
wakeupCounter.set(0);
}
if (close) {
// 執行事件佇列中的事件執行緒
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;
// 根據向selector中註冊的key遍歷channel中已經就緒的keys，並處理這些key
// Walk through the collection of ready keys and dispatch
// any active event.
while (iterator != null && iterator.hasNext()) {
SelectionKey sk = iterator.next();
// 這裡的attachment方法返回的就是在register()方法中註冊的
// 而KeyAttachment物件是對socket的包裝
KeyAttachment attachment = (KeyAttachment)sk.attachment();
// Attachment may be null if another thread has called
// cancelledKey()
if (attachment == null) {
iterator.remove();
} else {
// 更新通道最近一次發生事件的時間
// 防止因超時沒有事件發生而被剔除出selector
attachment.access();
iterator.remove();
// 具體處理通道的邏輯
processKey(sk, attachment);
}
}//while
//process timeouts
// 多路複用器每執行一遍完整的輪詢便檢視所有通道是否超時
// 對超時的通道將會被剔除出多路複用器
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();
}
// 處理selector檢測到的通道事件
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 ) {
// 確保通道不會因超時而被剔除
attachment.access();//make sure we don't time out valid sockets
sk.attach(attachment);//cant remember why this is here
NioChannel channel = attachment.getChannel();
// 處理通道發生的讀寫事件
if (sk.isReadable() || sk.isWritable() ) {
if ( attachment.getSendfileData() != null ) {
processSendfile(sk,attachment, false);
} else {
if ( isWorkerAvailable() ) {
// 在通道上登出對已經發生事件的關注
unreg(sk, attachment, sk.readyOps());
boolean closeSocket = false;
// Read goes before write
if (sk.isReadable()) {
// 具體的通道處理邏輯
if (!processSocket(channel, SocketStatus.OPEN_READ, true)) {
closeSocket = true;
}
}
if (!closeSocket && sk.isWritable()) {
if (!processSocket(channel, SocketStatus.OPEN_WRITE, true)) {
closeSocket = true;
}
}
if (closeSocket) {
// 解除無效通道
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;
}
// 這個unreg()很巧妙，防止了通道對同一個事件不斷select的問題
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註冊感興趣的事件，具體程式碼看下面的PollerEvent類的說明
protected void reg(SelectionKey sk, KeyAttachment attachment, int intops) {
sk.interestOps(intops);
attachment.interestOps(intops);
attachment.setCometOps(intops);
}
}
複製程式碼6.PollerEvent 處理流程
Poller 處理的核心是啟動執行事件佇列中的 PollerEvent，接著從 selector 中遍歷已經就緒的 key ，一旦發生了感興趣的事件，則交由 processSocket 方法處理。PollerEvent 的作用是向 socket 註冊或更新感興趣的事件：
/**
*
* PollerEvent, cacheable object for poller events to avoid GC
*/
public static class PollerEvent implements Runnable {
// 每個PollerEvent都會儲存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第一次註冊到selector中，完成對socket讀事件的註冊
if ( interestOps == OP_REGISTER ) {
try {
socket.getIOChannel().register(socket.getPoller().getSelector(), SelectionKey.OP_READ, key);
} catch (Exception x) {
log.error("", x);
}
} else {
// socket之前已經註冊到了selector中，更新socket所感興趣的事件
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
// 重新整理事件的最後訪問時間，防止事件超時
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+"]";
}
}
複製程式碼7.將 socket 交給 Worker 執行
在第5步的 Poller 處理流程的分析中看到它的 run 方法最後會呼叫 processKey() 處理 selector 檢測到的通道事件，而在這個方法最後會呼叫 processSocket 來呼叫具體的通道處理邏輯，看下 processSocket 方法的實現：
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
// 從SocketProcessor的快取佇列中取出一個來處理socket
SocketProcessor sc = processorCache.poll();
if ( sc == null ) sc = new SocketProcessor(socket,status);
else sc.reset(socket,status);
// 將有事件發生的socket交給Worker處理
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;
}
複製程式碼Poller 通過 NioEndpoint 的協調，將發生事件的 socket 交給工作者執行緒 Worker 來進一步處理。整個事件框架的工作就到此結束，下面就是 Worker 的處理。
8.從 socket 中處理請求
在 Tomcat 6 版本的 NIO 處理實現中有一個 Worker 類，在 Tomcat 7 中把它去掉了，但工作者的職責還在，只是交由了上面看到的 SocketProcessor 這個類來擔當，看下這個類的實現程式碼：
// ---------------------------------------------- SocketProcessor Inner Class
// 這個類相當於一個工作者，但只會在一個外部執行緒池中簡單使用。
/**
* This class is the equivalent of the Worker, but will simply use in an
* external Executor thread pool.
*/
protected class SocketProcessor implements Runnable {
// 每個SocketProcessor儲存一個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() {
// 從socket中獲取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) {
// 最關鍵的程式碼，這裡將KeyAttachment(實際就是socket)交給Handler處理請求
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) {
...
}
}
複製程式碼可以看到由 SocketProcessor 尋找合適的 Handler 處理器做最終 socket 轉換處理。
可以用下面這幅圖總結一下 NioEndpoint 的主要流程：
Acceptor 和 Poller 是執行緒陣列，Worker 是一個執行緒池（ Executor ）