mina架构分析
使用的版本号是2.0.9
IoService分析
extends SocketAddress> localAddresses) throws Exception {
// Create a bind request as a Future operation. When the selector
// have handled the registration, it will signal this future.
AcceptorOperationFuture request = new AcceptorOperationFuture(localAddresses);//这个future是一个用于线程间异步通信结果的类。它能够不被中断的等待异步操作的结果
// adds the Registration request to the queue for the Workers
// to handle
registerQueue.add(request);
// creates the Acceptor instance and has the local
// executor kick it off.
startupAcceptor();//这里启动acceptor线程
// As we just started the acceptor, we have to unblock the select()
// in order to process the bind request we just have added to the
// registerQueue.
try {
lock.acquire();//lock是一个semaphone，用于同步acceptor线程，保证该线程在成功创建并開始执行后。再执行兴许的代码
// Wait a bit to give a chance to the Acceptor thread to do the select()
Thread.sleep(10);
wakeup();//这是一个派生类须要实现的接口
} finally {
lock.release();
}
// Now, we wait until this request is completed.
request.awaitUninterruptibly();//这里异步等待acceptor线程设置结果。并导致当前线程被唤醒
if (request.getException() != null) {
throw request.getException();
}
// Update the local addresses.
// setLocalAddresses() shouldn't be called from the worker thread
// because of deadlock.
Set<SocketAddress> newLocalAddresses = new HashSet<SocketAddress>();
for (H handle : boundHandles.values()) {
newLocalAddresses.add(localAddress(handle));
}
return newLocalAddresses;
}
/**
* This method is called by the doBind() and doUnbind()
* methods. If the acceptor is null, the acceptor object will
* be created and kicked off by the executor. If the acceptor
* object is null, probably already created and this class
* is now working, then nothing will happen and the method
* will just return.
*/
private void startupAcceptor() throws InterruptedException {
// If the acceptor is not ready, clear the queues
// TODO : they should already be clean : do we have to do that ?
if (!selectable) {
registerQueue.clear();
cancelQueue.clear();
}
// start the acceptor if not already started
Acceptor acceptor = acceptorRef.get();
if (acceptor == null) {
lock.acquire();
acceptor = new Acceptor();//创建Acceptor实例
if (acceptorRef.compareAndSet(null, acceptor)) {
executeWorker(acceptor);//启动acceptor线程
} else {
lock.release();
}
}
}
public void run() {
assert (acceptorRef.get() == this);
int nHandles = 0;
// Release the lock
lock.release();//进程開始执行了，释放lock
while (selectable) {
try {
// Detect if we have some keys ready to be processed
// The select() will be woke up if some new connection
// have occurred, or if the selector has been explicitly
// woke up
int selected = select();//调用select接口，派生类须要实现之
// this actually sets the selector to OP_ACCEPT,
// and binds to the port on which this class will
// listen on
nHandles += registerHandles();//遍历registerQueue中的绑定请求，并调用open接口。实际上就是由派生类实现bind地址的功能。
// Now, if the number of registred handles is 0, we can
// quit the loop: we don't have any socket listening
// for incoming connection.
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) {
// We have some connection request, let's process
// them here.
processHandles(selectedHandles());//调用accept函数接收用户请求，创建Session，并把session增加到processor中
}
// check to see if any cancellation request has been made.
nHandles -= unregisterHandles();
} catch (ClosedSelectorException cse) {
// If the selector has been closed, we can exit the loop
ExceptionMonitor.getInstance().exceptionCaught(cse);
break;
} catch (Exception e) {
ExceptionMonitor.getInstance().exceptionCaught(e);
try {
Thread.sleep(1000);
} catch (InterruptedException e1) {
ExceptionMonitor.getInstance().exceptionCaught(e1);
}
}
}
// Cleanup all the processors, and shutdown the acceptor.
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();
}
}
}
}
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为了深入理解Session。我们须要了解例如以下几个问题：
protected NioSession accept(IoProcessor<NioSession> processor, ServerSocketChannel handle) throws Exception {
SelectionKey key = null;
if (handle != null) {
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);
}
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);
}
}
。
。
。
// Now, we can write the message. First, create a future
WriteFuture writeFuture = new DefaultWriteFuture(this);
WriteRequest writeRequest = new DefaultWriteRequest(message, writeFuture, remoteAddress);
// Then, get the chain and inject the WriteRequest into it
IoFilterChain filterChain = getFilterChain();
filterChain.fireFilterWrite(writeRequest);
。。。
// Return the WriteFuture.
return writeFuture;
}
它的fireFilterWrite方法实际上是，从tail到head遍历链表，既然是反向遍历。那么Head是最后一个被遍历到的filter。这个head是一个HeadFilter实例
@SuppressWarnings("unchecked")
@Override
public void filterWrite(NextFilter nextFilter, IoSession session, WriteRequest writeRequest) throws Exception {
AbstractIoSession s = (AbstractIoSession) session;
// Maintain counters.
if (writeRequest.getMessage() instanceof IoBuffer) {
IoBuffer buffer = (IoBuffer) writeRequest.getMessage();
// I/O processor implementation will call buffer.reset()
// it after the write operation is finished, because
// the buffer will be specified with messageSent event.
buffer.mark();
int remaining = buffer.remaining();
if (remaining > 0) {
s.increaseScheduledWriteBytes(remaining);
}
} else {
s.increaseScheduledWriteMessages();
}
WriteRequestQueue writeRequestQueue = s.getWriteRequestQueue();//获取session中的写请求队列
if (!s.isWriteSuspended()) {
if (writeRequestQueue.isEmpty(session)) {
// We can write directly the message
s.getProcessor().write(s, writeRequest);//使用processor写writeRequest，实际上还是把writeRequest写入到写请求队列中了
} else {
s.getWriteRequestQueue().offer(s, writeRequest);
s.getProcessor().flush(s);
}
} else {
s.getWriteRequestQueue().offer(s, writeRequest);//把writeRequest写入到写请求队列中
}
}
@SuppressWarnings("unchecked")
@Override
public void filterClose(NextFilter nextFilter, IoSession session) throws Exception {
((AbstractIoSession) session).getProcessor().remove(session);
}
}
那么问题来了。这个写队列是从哪冒出来的，它是怎样创建，又是谁从这个队列中把写请求取出来，发送出去的呢？
protected final void initSession(IoSession session, IoFuture future, IoSessionInitializer sessionInitializer) {
。。
。
// Every property but attributeMap should be set now.
// Now initialize the attributeMap. The reason why we initialize
// the attributeMap at last is to make sure all session properties
// such as remoteAddress are provided to IoSessionDataStructureFactory.
try {
((AbstractIoSession) session).setAttributeMap(session.getService().getSessionDataStructureFactory()
.getAttributeMap(session));
} catch (IoSessionInitializationException e) {
throw e;
} catch (Exception e) {
throw new IoSessionInitializationException("Failed to initialize an attributeMap.", e);
}
try {
((AbstractIoSession) session).setWriteRequestQueue(session.getService().getSessionDataStructureFactory()
.getWriteRequestQueue(session));
} catch (IoSessionInitializationException e) {
throw e;
} catch (Exception e) {
throw new IoSessionInitializationException("Failed to initialize a writeRequestQueue.", e);
}
if ((future != null) && (future instanceof ConnectFuture)) {
// DefaultIoFilterChain will notify the future. (We support ConnectFuture only for now).
session.setAttribute(DefaultIoFilterChain.SESSION_CREATED_FUTURE, future);
}
if (sessionInitializer != null) {
sessionInitializer.initializeSession(session, future);
}
finishSessionInitialization0(session, future);
}
好吧，我们还得接着寻找。session.getService是谁呢？这里的session显然是NioSession，service是NioSocketAcceptor，getSessionDataStructureFactory方法是在基类AbstractIoService中定义的。在默认情况下。get出来的实例。是DefaultIoSessionDataStructureFactory的类实例。我们再来看这个类
public IoSessionAttributeMap getAttributeMap(IoSession session) throws Exception {
return new DefaultIoSessionAttributeMap();
}
public WriteRequestQueue getWriteRequestQueue(IoSession session) throws Exception {
return new DefaultWriteRequestQueue();
}
private static class DefaultIoSessionAttributeMap implements IoSessionAttributeMap {
private final ConcurrentHashMap<Object, Object> attributes = new ConcurrentHashMap<Object, Object>(4);
/** A queue to store incoming write requests */
private final Queue<WriteRequest> q = new ConcurrentLinkedQueue<WriteRequest>();
。。
WriteRequestQueue writeRequestQueue = session.getWriteRequestQueue();
writeRequestQueue.offer(session, writeRequest);
if (!session.isWriteSuspended()) {
this.flush(session);
}
}
.getAttributeMap(session));
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public void run() {
assert (processorRef.get() == this);
int nSessions = 0;
lastIdleCheckTime = System.currentTimeMillis();
for (;;) {
try {
// This select has a timeout so that we can manage
// idle session when we get out of the select every
// second. (note : this is a hack to avoid creating
// a dedicated thread).
long t0 = System.currentTimeMillis();
int selected = select(SELECT_TIMEOUT);//select事件，看是否有读写，关闭事件发生
long t1 = System.currentTimeMillis();
long delta = (t1 - t0);
if ((selected == 0) && !wakeupCalled.get() && (delta < 100)) {
// Last chance : the select() may have been
// interrupted because we have had an closed channel.
if (isBrokenConnection()) {
LOG.warn("Broken connection");
// we can reselect immediately
// set back the flag to false
wakeupCalled.getAndSet(false);
continue;
} else {
LOG.warn("Create a new selector. Selected is 0, delta = " + (t1 - t0));
// Ok, we are hit by the nasty epoll
// spinning.
// Basically, there is a race condition
// which causes a closing file descriptor not to be
// considered as available as a selected channel, but
// it stopped the select. The next time we will
// call select(), it will exit immediately for the same
// reason, and do so forever, consuming 100%
// CPU.
// We have to destroy the selector, and
// register all the socket on a new one.
registerNewSelector();
}
// Set back the flag to false
wakeupCalled.getAndSet(false);
// and continue the loop
continue;
}
// Manage newly created session first
nSessions += handleNewSessions();//这里会处理newSessions，就是在acceptor线程中add进来的，基本上来说。就是创建filterChain，并触发sessionCreated事件和sessionOpen事件。
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();//这里会对发生了事件的session进行处理。假设session是读事件，会调用session底层的channel去读数据，并触发session的messageReceived时间，假设session是写事件。会把session增加到flushingSessions队列里
}
// Write the pending requests
long currentTime = System.currentTimeMillis();
flush(currentTime);//这里会处理flushingSessions队列。调用session底层的channel去发送数据
// And manage removed sessions
nSessions -= removeSessions();
// Last, not least, send Idle events to the idle sessions
notifyIdleSessions(currentTime);
// Get a chance to exit the infinite loop if there are no
// more sessions on this Processor
if (nSessions == 0) {
processorRef.set(null);
if (newSessions.isEmpty() && isSelectorEmpty()) {
// newSessions.add() precedes startupProcessor
assert (processorRef.get() != this);
break;
}
assert (processorRef.get() != this);
if (!processorRef.compareAndSet(null, this)) {
// startupProcessor won race, so must exit processor
assert (processorRef.get() != this);
break;
}
assert (processorRef.get() == this);
}
// Disconnect all sessions immediately if disposal has been
// requested so that we exit this loop eventually.
if (isDisposing()) {
for (Iterator<S> i = allSessions(); i.hasNext();) {
scheduleRemove(i.next());
}
wakeup();
}
} catch (ClosedSelectorException cse) {
// If the selector has been closed, we can exit the loop
// But first, dump a stack trace
ExceptionMonitor.getInstance().exceptionCaught(cse);
break;
} catch (Exception e) {
ExceptionMonitor.getInstance().exceptionCaught(e);
try {
Thread.sleep(1000);
} catch (InterruptedException e1) {
ExceptionMonitor.getInstance().exceptionCaught(e1);
}
}
}
try {
synchronized (disposalLock) {
if (disposing) {
doDispose();
}
}
} catch (Exception e) {
ExceptionMonitor.getInstance().exceptionCaught(e);
} finally {
disposalFuture.setValue(true);
}
}
}
这些processor线程是用来检查是否有读写事件的。
用户加入到filterChain的filter都是在这个线程中运行的，最后会把事件传递给handler进行终于的处理。也就是说。当有多个session的时候，会有多个processor线程，session的个数是大于等于processor的个数的。
同一时候，一个processor会相应多个session，单一个session仅仅相应一个processor线程。
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