EndPoint的组件就是属于连接器Connector里面的。它是一个通信的端点，就是负责对外实现TCP/IP协议。EndPoint是个接口，它的具体实现类就是AbstractEndpoint，而AbstractEndpoint具体的实现类就有AprEndpoint、Nio2Endpoint、NioEndpoint。
AprEndpoint：对应的是APR模式，简单理解就是从操作系统级别解决异步IO的问题，大幅度提高服务器的处理和响应性能。但是启用这种模式需要安装一些其他的依赖库。
Nio2Endpoint：利用代码来实现异步IO
NioEndpoint：利用了JAVA的NIO实现了非阻塞IO，Tomcat默认启动是以这个来启动的，而这个也是我们的讲述重点。
在代码NioEndpoint.class中定义的这五个组件。具体这五个组件是干嘛的呢？
LimitLatch：连接控制器，负责控制最大的连接数
Acceptor：负责接收新的连接，然后返回一个Channel对象给Poller
Poller：可以将其看成是NIO中Selector，负责监控Channel的状态
SocketProcessor：可以看成是一个被封装的任务类
Executor：Tomcat自己扩展的线程池，用来执行任务类
组件间的关联关系：
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启动NioEndpoint的Acceptor多线程，默认初始化一个Acceptor：此处与8之前的版本有更新！！！
package org.apache.tomcat.util.net；
public abstract class AbstractEndpoint<S>
/**
* Acceptor是接收连接的，我们可以看到Acceptor实现了Runnable接口，
* 那么在哪会新开启线程来执行Acceptor的run方法呢？
* 在AbstractEndpoint的startAcceptorThreads方法中。
*/
protected final void startAcceptorThreads() {
int count = getAcceptorThreadCount();
acceptors = new Acceptor[count];
for (int i = 0; i < count; i++) {
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();
}
}
@Override
protected AbstractEndpoint.Acceptor createAcceptor() {
return new Acceptor();
}
具体类的实现内容：
1、执行run方法，启动socket服务；
2、关闭socket服务。
/**
* The background thread that listens for incoming TCP/IP connections and
* hands them off to an appropriate processor.
* 重要方法
*/
protected class Acceptor extends AbstractEndpoint.Acceptor {
@Override
public void run() {
int errorDelay = 0;
// 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 {
//if we have reached max connections, wait （默认是 private int maxConnections = 10000;）
countUpOrAwaitConnection();
SocketChannel socket = null;
try {
// Accept the next incoming connection from the server
// socket
socket = serverSock.accept();
} catch (IOException ioe) {
// We didn't get a socket
countDownConnection();
if (running) {
// 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 (running && !paused) {
// setSocketOptions() will hand the socket off to
// an appropriate processor if successful
if (!setSocketOptions(socket)) {
closeSocket(socket);
}
} else {
closeSocket(socket);
}
} catch (Throwable t) {
ExceptionUtils.handleThrowable(t);
log.error(sm.getString("endpoint.accept.fail"), t);
}
}
state = AcceptorState.ENDED;
}
private void closeSocket(SocketChannel socket) {
countDownConnection();
try {
socket.socket().close();
} catch (IOException ioe) {
if (log.isDebugEnabled()) {
log.debug(sm.getString("endpoint.err.close"), ioe);
}
}
try {
socket.close();
} catch (IOException ioe) {
if (log.isDebugEnabled()) {
log.debug(sm.getString("endpoint.err.close"), ioe);
}
}
}
}
package sun.nio.ch;
ServerSocketChannelImpl.class
public SocketChannel accept() throws IOException {
synchronized(this.lock) {
if (!this.isOpen()) {
throw new ClosedChannelException();
} else if (!this.isBound()) {
throw new NotYetBoundException();
} else {
SocketChannelImpl var2 = null;
int var3 = 0;
FileDescriptor var4 = new FileDescriptor();
InetSocketAddress[] var5 = new InetSocketAddress[1];
InetSocketAddress var6;
try {
this.begin();
if (!this.isOpen()) {
var6 = null;
return var6;
}
this.thread = NativeThread.current();
do {
var3 = this.accept(this.fd, var4, var5);
} while(var3 == -3 && this.isOpen());
} finally {
this.thread = 0L;
this.end(var3 > 0);
assert IOStatus.check(var3);
}
if (var3 < 1) {
return null;
} else {
IOUtil.configureBlocking(var4, true);
var6 = var5[0];
var2 = new SocketChannelImpl(this.provider(), var4, var6);
SecurityManager var7 = System.getSecurityManager();
if (var7 != null) {
try {
var7.checkAccept(var6.getAddress().getHostAddress(), var6.getPort());
} catch (SecurityException var13) {
var2.close();
throw var13;
}
}
return var2;
}
}
}
}
private int accept(FileDescriptor var1, FileDescriptor var2, InetSocketAddress[] var3) throws IOException {
return this.accept0(var1, var2, var3);
}
private native int accept0(FileDescriptor var1, FileDescriptor var2, InetSocketAddress[] var3) throws IOException;
