本文详细解读了mina服务器的请求处理模型，包括acceptor模型、filterchain和processor处理模型，以及核心组件如acceptor、niosession、nioprocessor的实现原理。重点介绍了socket连接的管理、异步IO操作、过滤器链的构建与扩展，以及处理器如何调度任务。通过实例代码分析，展示了mina如何高效地处理并发连接。
最近阅读了mina的源代码，这里给大家做个分享:
一、mina server请求处理模型
下面的几张图对大家后面的理解会有一定的帮助，先贴出来:
1.acceptor模型:
2.filterchain和processor处理模型
二、mina server核心组件剖析
1.acceptor:
首先附上一张acceptor的uml图,方面大家了阅读源码时了解到我们讲到的一些细节：
mina框架中负责监听连接的类，使用单个线程运行。使用nio的selector实现。将serversocketchannel的accept注册到selector中，使用单个线程轮训选择器的方式不断检测是否有新的连接进入。在Acceptor类中你会看到如下代码：
while (selectable) {
try {
int selected = select();
nHandles += registerHandles();
if (nHandles == 0) {
acceptorRef.set(null);
if (registerQueue.isEmpty() && cancelQueue.isEmpty()) {
assert (acceptorRef.get() != this);
break;
}
if (!acceptorRef.compareAndSet(null, this)) {
assert (acceptorRef.get() != this);
break;
}
assert (acceptorRef.get() == this);
}
if (selected > 0) {
processHandles(selectedHandles());
}
} 我们从registerHandles方法开始读起，这方法中会在acceptor自己的选择器中注册serversocketchannel，并将accept标记为感兴趣的事件。选择器是java nio中异步的基础，这里我做下简单的介绍。首先有几个概念需要提一下，1.
SelectableChannel 2.selector 3.selectkey。java nio中所有继承至SelectableChannel的类都是可以做异步io的，那什么是异步io呢？这是相对于同步io来说的，如果你使用的是同步io，当你需要从本机socket中读数据，但是socket的buffer中又没有数据的情况下，当前线程是要被block住的。而使用异步io，即使socket的buffer中没有数据，当前线程可以不被阻塞掉，而可以去做其他事情。selector是java能做异步io的重要组件，其最重要的功能就是就绪选择，这是java socket异步通信的基础。每个SelectableChannel都可以将自己感兴趣的操作注册到selector中，当自己感兴趣的操作被选择器确定为已就绪时，SelectableChannel就可以进行相应的处理。那你肯定要问SelectableChannel和selector是通过什么联系起来的？答案就是selectkey，每一个注册进selector的SelectableChannel都会生成一个selectkey，这个selectkey标示了当前SelectableChannel的状态。selector中维护了三个selectkey集合：1.已选择的selectkey集合。2.已注册的selectkey集合。3.已取消的selectkey集合。每次调用selector的select方法时，都会更新一次选择键的集合，这里我们比较关心的是已选择的selectkey集合。mian中的acceptor和nioprocessor都是使用selector实现的，这就让单个线程可以处理很多请求，你可能不会想像到，mina维护socket连接的线程只有一个(acceptor)，你在稍后的代码中就可以看到。先看下serversocketchannle是如何在selector中注册自身的：
private int registerHandles() {
for (;;) {
// The register queue contains the list of services to manage
// in this acceptor.
AcceptorOperationFuture future = registerQueue.poll();
if (future == null) {
return 0;
}
// We create a temporary map to store the bound handles,
// as we may have to remove them all if there is an exception
// during the sockets opening.
Map<SocketAddress, H> newHandles = new ConcurrentHashMap<SocketAddress, H>();
List<SocketAddress> localAddresses = future.getLocalAddresses();
try {
// Process all the addresses
for (SocketAddress a : localAddresses) {
H handle = open(a);
newHandles.put(localAddress(handle), handle);
}
..............再次进入到open方法：
// Creates the listening ServerSocket
ServerSocketChannel channel = ServerSocketChannel.open();
boolean success = false;
try {
// This is a non blocking socket channel
channel.configureBlocking(false);
// Configure the server socket,
ServerSocket socket = channel.socket();
// Set the reuseAddress flag accordingly with the setting
socket.setReuseAddress(isReuseAddress());
// and bind.
socket.bind(localAddress, getBacklog());
// Register the channel within the selector for ACCEPT event
channel.register(selector, SelectionKey.OP_ACCEPT);
success = true;
} finally {
if (!success) {
close(channel);
}
}
return channel;
如上所示，serversocketchannle将自身注册到了acceptor的selector当中，并将accept事件标记为感兴趣的事件，每当有新的socket连接建立时，accept事件都会被触发，当调用selector的select方法时，selector中的已选择的选择键集合就会被更新，然后通过选择键可以获取到serversocketchannel，调用serversocketchannel的accept方法就可以拿到新的socket连接的socketchannel。这个在稍后负责建立连接的acceptor线程中可以看到。我们继续阅读第一段代码，你会看到：
if (selected > 0) {
processHandles(selectedHandles());
} selected是selector.select()的结果，当有通道被选择器选择时，selected的值就会>0。selectedHadnles方法会返回一个可遍历的已选择的选择键集合,我们直接进入processHandles方法:
private void processHandles(Iterator<H> handles) throws Exception {
while (handles.hasNext()) {
H handle = handles.next();
handles.remove();
// Associates a new created connection to a processor,
// and get back a session
S session = accept(processor, handle);
if (session == null) {
continue;
}
initSession(session, null, null);
// add the session to the SocketIoProcessor
session.getProcessor().add(session);
}
}
}以上代码对以选择的选择键进行了遍历,accept选择键遍历出，然后从中获取新的连接对应的serversocketchannel并将其放入到NioSession中，mina会将每一个连接对应的socketchannel都放入到一个新的niosession中，你可以将niosession理解为对一个连接会话的抽象。稍后我会着重将下niosession的实现，里面有一个filterchain是mina可扩展业务模型的核心。现在我们进入accept方法中看下：
@Override
protected NioSession accept(IoProcessor<NioSession> processor, ServerSocketChannel handle) throws Exception {
SelectionKey key = handle.keyFor(selector);
if ((key == null) || (!key.isValid()) || (!key.isAcceptable())) {
return null;
}
// accept the connection from the client
SocketChannel ch = handle.accept();
if (ch == null) {
return null;
}
return new NioSocketSession(this, processor, ch);
}正如我刚才说的这里会拿出新连接的socketchannel并将他放入到niosesison中。NioSocketSession对象的构造函数中的processor是一个processor对象池，这是在acceptor初始化的时候建立的，接下来我们就进入niosession的源码阅读。
2.niosession
和上面一样，首先附上一张niosession的uml图：
niosocketSession中一个比较核心的东西就是filterchain,看到filter就觉得很熟悉吧？会把他和用户自定义的filter进行联系？没错这个filterchain就包含了用户自定义的filter以及用户自定义的handler。看到filter我的第一感觉就是mina应该会用职责链的设计模式来将filterchain做成可扩展的设计。我们进入NioSession看看filterchain是如何被初始化的：
protected NioSession(IoProcessor<NioSession> processor, IoService service, Channel channel) {
super(service);
this.channel = channel;
this.processor = processor;
filterChain = new DefaultIoFilterChain(this);
}接着进入DefaultIoFilterChain的构造函数：
public DefaultIoFilterChain(AbstractIoSession session) {
if (session == null) {
throw new IllegalArgumentException("session");
}
this.session = session;
head = new EntryImpl(null, null, "head", new HeadFilter());
tail = new EntryImpl(head, null, "tail", new TailFilter());
head.nextEntry = tail;
}这是比较关键的地方，filterchain在初始化的时候会构建两个默认的filter：headfilter和tailfiter，看他们的名字应该能想到他们是处理链的头和尾。这两个filter分别被封装进两个entry中，并组成了entry链，进入EntryImpl的构造方法:
private EntryImpl(EntryImpl prevEntry, EntryImpl nextEntry, String name, IoFilter filter) {
if (filter == null) {
throw new IllegalArgumentException("filter");
}
if (name == null) {
throw new IllegalArgumentException("name");
}
this.prevEntry = prevEntry;
this.nextEntry = nextEntry;
this.name = name;
this.filter = filter;
this.nextFilter = new NextFilter() {
public void sessionCreated(IoSession session) {
Entry nextEntry = EntryImpl.this.nextEntry;
callNextSessionCreated(nextEntry, session);
}
public void sessionOpened(IoSession session) {
Entry nextEntry = EntryImpl.this.nextEntry;
callNextSessionOpened(nextEntry, session);
}
public void sessionClosed(IoSession session) {
Entry nextEntry = EntryImpl.this.nextEntry;
callNextSessionClosed(nextEntry, session);
}
public void sessionIdle(IoSession session, IdleStatus status) {
Entry nextEntry = EntryImpl.this.nextEntry;
callNextSessionIdle(nextEntry, session, status);
}
public void exceptionCaught(IoSession session, Throwable cause) {
Entry nextEntry = EntryImpl.this.nextEntry;
callNextExceptionCaught(nextEntry, session, cause);
}
public void messageReceived(IoSession session, Object message) {
Entry nextEntry = EntryImpl.this.nextEntry;
callNextMessageReceived(nextEntry, session, message);
}
public void messageSent(IoSession session, WriteRequest writeRequest) {
Entry nextEntry = EntryImpl.this.nextEntry;
callNextMessageSent(nextEntry, session, writeRequest);
}
public void filterWrite(IoSession session, WriteRequest writeRequest) {
Entry nextEntry = EntryImpl.this.prevEntry;
callPreviousFilterWrite(nextEntry, session, writeRequest);
}
public void filterClose(IoSession session) {
Entry nextEntry = EntryImpl.this.prevEntry;
callPreviousFilterClose(nextEntry, session);
}
public String toString() {
return EntryImpl.this.nextEntry.name;
}
};
}从上面的代码可以看到，每个entryimpl都包含preentry、nextentry、filter、nextfilter这几个关键的属性。你现在能想像到mina的职责链是如何设计的吗？我们随机挑选一个call**方法就很清楚了：
private void callNextSessionCreated(Entry entry, IoSession session) {
try {
IoFilter filter = entry.getFilter();
NextFilter nextFilter = entry.getNextFilter();
filter.sessionCreated(nextFilter, session);
} catch (Throwable e) {
fireExceptionCaught(e);
}
}哈哈，真相就在这里，注意方法中entry入參，这里的entry对象传入的是当前entry的nextentry。这里执行了filterchain中当前链节点下一个链节点的xxx方法，而nexfilterchain中的方法又对下下个链节点中的filter进行了xxx方法的调用。可以想到，如果要在处理链中加入自己的filter，你只需要在filter中实现自己的业务逻辑，在最后调用下xxx方法，并把nextfilter做成如參传入。关于用户自定义的链是如何被加入到filterchain中的以及handler是如何被扩展、如何被处理的，我在稍后会提到。大概过完niosession的filterchain，现在我们继续进入下一个环节，nioprocessor.
3.processor
我们回到刚才的主线代码继续阅读：
进入acceptor的processHandles方法：
private void processHandles(Iterator<H> handles) throws Exception {
while (handles.hasNext()) {
H handle = handles.next();
handles.remove();
// Associates a new created connection to a processor,
// and get back a session
S session = accept(processor, handle);
if (session == null) {
continue;
}
initSession(session, null, null);
// add the session to the SocketIoProcessor
session.getProcessor().add(session);
}
}
private IoProcessor<S> getProcessor(S session) {
IoProcessor<S> processor = (IoProcessor<S>) session.getAttribute(PROCESSOR);
if (processor == null) {
if (disposed || disposing) {
throw new IllegalStateException("A disposed processor cannot be accessed.");
}
processor = pool[Math.abs((int) session.getId()) % pool.length];
if (processor == null) {
throw new IllegalStateException("A disposed processor cannot be accessed.");
}
session.setAttributeIfAbsent(PROCESSOR, processor);
}
return processor;
}
public final void add(S session) {
if (disposed || disposing) {
throw new IllegalStateException("Already disposed.");
}
// Adds the session to the newSession queue and starts the worker
newSessions.add(session);
startupProcessor();
}
private void startupProcessor() {
Processor processor = processorRef.get();
if (processor == null) {
processor = new Processor();
if (processorRef.compareAndSet(null, processor)) {
executor.execute(new NamePreservingRunnable(processor, threadName));
}
}
// Just stop the select() and start it again, so that the processor
// can be activated immediately.
wakeup();
}
// Manage newly created session first
nSessions += handleNewSessions();
updateTrafficMask();
// Now, if we have had some incoming or outgoing events,
// deal with them
if (selected > 0) {
//LOG.debug("Processing ..."); // This log hurts one of the MDCFilter test...
process();
}
// Write the pending requests
long currentTime = System.currentTimeMillis();
flush(currentTime);
// And manage removed sessions
nSessions -= removeSessions();
private int handleNewSessions() {
int addedSessions = 0;
for (S session = newSessions.poll(); session != null; session = newSessions.poll()) {
if (addNow(session)) {
// A new session has been created
addedSessions++;
}
}
return addedSessions;
}
private boolean addNow(S session) {
boolean registered = false;
try {
init(session);
registered = true;
// Build the filter chain of this session.
IoFilterChainBuilder chainBuilder = session.getService().getFilterChainBuilder();
chainBuilder.buildFilterChain(session.getFilterChain());
// DefaultIoFilterChain.CONNECT_FUTURE is cleared inside here
// in AbstractIoFilterChain.fireSessionOpened().
// Propagate the SESSION_CREATED event up to the chain
IoServiceListenerSupport listeners = ((AbstractIoService) session.getService()).getListeners();
listeners.fireSessionCreated(session);
} catch (Throwable e) {
ExceptionMonitor.getInstance().exceptionCaught(e);
try {
destroy(session);
} catch (Exception e1) {
ExceptionMonitor.getInstance().exceptionCaught(e1);
} finally {
registered = false;
}
}
return registered;
}protected void init(NioSession session) throws Exception {
SelectableChannel ch = (SelectableChannel) session.getChannel();
ch.configureBlocking(false);
session.setSelectionKey(ch.register(selector, SelectionKey.OP_READ, session));
}public void buildFilterChain(IoFilterChain chain) throws Exception {
for (Entry e : entries) {
chain.addLast(e.getName(), e.getFilter());
}
}public synchronized void addLast(String name, IoFilter filter) {
checkAddable(name);
register(tail.prevEntry, name, filter);
}
private void register(EntryImpl prevEntry, String name, IoFilter filter) {
EntryImpl newEntry = new EntryImpl(prevEntry, prevEntry.nextEntry, name, filter);
try {
filter.onPreAdd(this, name, newEntry.getNextFilter());
} catch (Exception e) {
throw new IoFilterLifeCycleException("onPreAdd(): " + name + ':' + filter + " in " + getSession(), e);
}
prevEntry.nextEntry.prevEntry = newEntry;
prevEntry.nextEntry = newEntry;
name2entry.put(name, newEntry);
try {
filter.onPostAdd(this, name, newEntry.getNextFilter());
} catch (Exception e) {
deregister0(newEntry);
throw new IoFilterLifeCycleException("onPostAdd(): " + name + ':' + filter + " in " + getSession(), e);
}
}private static class TailFilter extends IoFilterAdapter {
public void sessionCreated(NextFilter nextFilter, IoSession session)
throws Exception {
session.getHandler().sessionCreated(session);
}
public void sessionOpened(NextFilter nextFilter, IoSession session)
throws Exception {
try {
session.getHandler().sessionOpened(session);
} finally {
// Notify the related ConnectFuture
// if the session is created from SocketConnector.
ConnectFuture future = (ConnectFuture) session
.removeAttribute(CONNECT_FUTURE);
if (future != null) {
future.setSession(session);
}
}
}
public void sessionClosed(NextFilter nextFilter, IoSession session)
throws Exception {
try {
session.getHandler().sessionClosed(session);
} finally {
// Remove all filters.
session.getFilterChain().clear();
}
}
....}
扫一扫
7482
被折叠的 条评论
为什么被折叠?
到【灌水乐园】发言
