Mina之polling
polling下面包含了实现了基于轮询策略的select调用或其他类型的I/O轮询系统调用的基类。先看抽象类AbstractPollingIoAcceptor，成员如下：
public abstract class AbstractPollingIoAcceptor<T extends AbstractIoSession, H> extends AbstractIoAcceptor {
private final IoProcessor<T> processor;
private final boolean createdProcessor;
private final Object lock = new Object();
private final Queue<AcceptorOperationFuture> registerQueue = new ConcurrentLinkedQueue<AcceptorOperationFuture>();
private final Queue<AcceptorOperationFuture> cancelQueue = new ConcurrentLinkedQueue<AcceptorOperationFuture>();
private final Map<SocketAddress, H> boundHandles = Collections.synchronizedMap(new HashMap<SocketAddress, H>());
private final ServiceOperationFuture disposalFuture = new ServiceOperationFuture();
private volatile boolean selectable;
private Acceptor acceptor;
}
registerQueue是注册队列，cancelQueue是取消注册的队列。boundHandles保存了地址到服务器socket的映射表。先看bind的处理过程：
protected final Set<SocketAddress> bindInternal(List<? extends SocketAddress> localAddresses) throws Exception {
// 创建一个BIND REQUEST作为Future Operation。
AcceptorOperationFuture request = new AcceptorOperationFuture(localAddresses);
// 添加到注册队列中
registerQueue.add(request);
// 创建Acceptor实例，然后启动它
startupAcceptor();
// select不会被阻塞，只需要把bind request添加到注册队列就好了。
wakeup();
// 等待知道request完成
request.awaitUninterruptibly();
if (request.getException() != null) {
throw request.getException();
}
//更新本地绑定地址
Set<SocketAddress> newLocalAddresses = new HashSet<SocketAddress>();
for (H handle:boundHandles.values()) {
newLocalAddresses.add(localAddress(handle));
}
return newLocalAddresses;
}
真正负责接受客户端请求的工作是Acceptor线程完成的，下面是其中的run方法：
public void run() {
int nHandles = 0;
while (selectable) {
try {
// 看一下有没有keys可以被处理了
int selected = select();
// 注册服务器，这样做的目的是讲Selector的状态至于OP_ACCEPT，并绑定到
// 监听的端口上，表明可以接受来自客户端的链接请求了。
nHandles += registerHandles();
if (selected > 0) {
// 处理OP_ACCEPT状态的服务器socket句柄集
processHandles(selectedHandles());
}
// 检查客户端取消的请求
nHandles -= unregisterHandles();
// 如果现在nHandles为0，那么就可以退出循环了。
if (nHandles == 0) {
synchronized (lock) {
if (registerQueue.isEmpty() && cancelQueue.isEmpty()) {
acceptor = null;
break;
}
}
}
} catch (Throwable e) {
ExceptionMonitor.getInstance().exceptionCaught(e);
try {
Thread.sleep(1000);
} catch (InterruptedException e1) {
ExceptionMonitor.getInstance().exceptionCaught(e1);
}
}
}
// 释放资源。
if (selectable && isDisposing()) {
selectable = false;
try {
if (createdProcessor) {
processor.dispose();
}
} finally {
try {
synchronized (disposalLock) {
if (isDisposing()) {
destroy();
}
}
} catch (Exception e) {
ExceptionMonitor.getInstance().exceptionCaught(e);
} finally {
disposalFuture.setDone();
}
}
}
}
下面通过registerHandles注册服务器socket句柄：
private int registerHandles() {
for (;;) {
// acceptor中注册队列包括services列表
AcceptorOperationFuture future = registerQueue.poll();
if (future == null) {
return 0;
}
// 我们建立临时的map保存
Map<SocketAddress, H> newHandles = new HashMap<SocketAddress, H>();
List<SocketAddress> localAddresses = future.getLocalAddresses();
try {
// 处理所有的地址
for (SocketAddress a : localAddresses) {
H handle = open(a);// 打开指定地址，返回服务器socket句柄
newHandles.put(localAddress(handle), handle);// 加入地址-socket映射表中
}
boundHandles.putAll(newHandles);// 更新本地绑定地址集
future.setDone();// 完成注册过程
return newHandles.size();
} catch (Exception e) {
future.setException(e);
} finally {
// 如果失败的话回滚
if (future.getException() != null) {
for (H handle : newHandles.values()) {
try {
close(handle);
} catch (Exception e) {
ExceptionMonitor.getInstance().exceptionCaught(e);
}
}
wakeup();
}
}
}
}
processHandles方法用来处理一个会话，只有准备好的才会被在这里处理：
// 处理来自客户端的请求
private void processHandles(Iterator<H> handles) throws Exception {
while (handles.hasNext()) {
H handle = handles.next();
handles.remove();
T session = accept(processor, handle);// 真正接受来自客户端的请求
if (session == null) {
break;
}
initSession(session, null, null);
session.getProcessor().add(session);// 加入
}
}
AbstractPollingIoConnector用于实现客户端连接的轮询策略，底层的socket不断地被检测，并当有任何一个socket需要被处理时就会被唤醒去处理：
public abstract class AbstractPollingIoConnector<T extends AbstractIoSession, H> extends AbstractIoConnector {
private final Object lock = new Object();
private final Queue<ConnectionRequest> connectQueue = new ConcurrentLinkedQueue<ConnectionRequest>();// 链接队列
private final Queue<ConnectionRequest> cancelQueue = new ConcurrentLinkedQueue<ConnectionRequest>(); // 取消队列
private final IoProcessor<T> processor;
private final boolean createdProcessor;
private final ServiceOperationFuture disposalFuture = new ServiceOperationFuture();
private volatile boolean selectable;
private Connector connector;
}
处理连接的方法，真正的操作也是在线程中进行的：
protected final ConnectFuture connect0(SocketAddress remoteAddress, SocketAddress localAddress, IoSessionInitializer<? extends ConnectFuture> sessionInitializer) {
H handle = null;
boolean success = false;
try {
handle = newHandle(localAddress);
if (connect(handle, remoteAddress)) {// 如果已链接服务器成功
ConnectFuture future = new DefaultConnectFuture();
T session = newSession(processor, handle);// 创建新会话
initSession(session, future, sessionInitializer);
session.getProcessor().add(session);// 将剩下的处理交给IoProcessor
success = true;
return future;
}
success = true;
} catch (Exception e) {
return DefaultConnectFuture.newFailedFuture(e);
} finally {
if (!success && handle != null) {
try {
close(handle);
} catch (Exception e) {
ExceptionMonitor.getInstance().exceptionCaught(e);
}
}
}
ConnectionRequest request = new ConnectionRequest(handle, sessionInitializer);
connectQueue.add(request);// 加入请求队列
startupWorker();// 开启工作线程处理连接请求
wakeup();// 中断select操作
return request;
}
真正的处理的线程：
public void run() {
int nHandles = 0;
while (selectable) {
try {
int timeout = (int)Math.min(getConnectTimeoutMillis(), 1000L);// 等待超时时间
int selected = select(timeout);// 在超时时间内看时候有可以的连接
nHandles += registerNew();// 取出连接请求，加入连接轮询池
if (selected > 0) {
nHandles -= processConnections(selectedHandles());// 处理连接请求
}
processTimedOutSessions(allHandles());// 处理超时连接请求
nHandles -= cancelKeys();// 取消了的会话
if (nHandles == 0) {
synchronized (lock) {
if (connectQueue.isEmpty()) {
connector = null;
break;
}
}
}
} catch (Throwable e) {
ExceptionMonitor.getInstance().exceptionCaught(e);
try {
Thread.sleep(1000);
} catch (InterruptedException e1) {
ExceptionMonitor.getInstance().exceptionCaught(e1);
}
}
}
if (selectable && isDisposing()) {
selectable = false;
try {
if (createdProcessor) {
processor.dispose();
}
} finally {
try {
synchronized (disposalLock) {
if (isDisposing()) {
destroy();
}
}
} catch (Exception e) {
ExceptionMonitor.getInstance().exceptionCaught(e);
} finally {
disposalFuture.setDone();
}
}
}
}
}
其实这里的代码就差不多都很清楚了（和前面的已经很相似，不在赘述）。
