Mina2.0框架源码剖析（六）

上文的内容还有一些没有结尾，这篇补上。在ExpiringMap类中，使用了一个私有内部类ExpiringObject来表示待检查超时的对象，它包括三个域，键，值，上次访问时间，以及用于上次访问时间这个域的读写锁：

Java代码

private
K key;

private
V value;

private

long
lastAccessTime;

private

final
ReadWriteLock lastAccessTimeLock =
new
ReentrantReadWriteLock();

private K key;
private V value;
private long lastAccessTime;
private final ReadWriteLock lastAccessTimeLock = new ReentrantReadWriteLock();

而ExpiringMap中包括了下述几个变量:

Java代码

private

final
ConcurrentHashMap<K, ExpiringObject> delegate;
//超时代理集合，保存待检查对象

private

final
CopyOnWriteArrayList<ExpirationListener<V>> expirationListeners;
//超时监听者

private

final
Expirer expirer;
//超时检查线程

private final ConcurrentHashMap<K, ExpiringObject> delegate;//超时代理集合，保存待检查对象
private final CopyOnWriteArrayList<ExpirationListener<V>> expirationListeners;//超时监听者
private final Expirer expirer;//超时检查线程

现在再来看看IoSession的一个抽象实现类AbstractIoSession。这是它的几个重要的成员变量：

Java代码

private
IoSessionAttributeMap attributes;
//会话属性映射图

private
WriteRequestQueue writeRequestQueue;
//写请求队列

private
WriteRequest currentWriteRequest;
//当前写请求

private IoSessionAttributeMap attributes;//会话属性映射图
private WriteRequestQueue writeRequestQueue;//写请求队列
private WriteRequest currentWriteRequest;//当前写请求

当要结束当前会话时，会发送一个一个写请求CLOSE_REQUEST。而closeFuture这个CloseFuture会在连接关闭时状态被设置为”closed”,它的监听器是SCHEDULED_COUNTER_RESETTER。

close和closeOnFlush都是异步的关闭操作，区别是前者立即关闭连接，而后者是在写请求队列中放入一个CLOSE_REQUEST，并将其即时刷新出去，若要真正等待关闭完成，需要调用方在返回的CloseFuture等待

Java代码

public

final
CloseFuture close() {

synchronized
(lock) {

if
(isClosing()) {

return
closeFuture;

} else
{

closing = true
;

}

}

getFilterChain().fireFilterClose();//fire出关闭事件

return
closeFuture;

}

public

final
CloseFuture closeOnFlush() {

getWriteRequestQueue().offer(this
, CLOSE_REQUEST);

getProcessor().flush(this
);

return
closeFuture;

}

public final CloseFuture close() {
synchronized (lock) {
if (isClosing()) {
return closeFuture;
} else {
closing = true;
}
}
getFilterChain().fireFilterClose();//fire出关闭事件
return closeFuture;
}

public final CloseFuture closeOnFlush() {
getWriteRequestQueue().offer(this, CLOSE_REQUEST);
getProcessor().flush(this);
return closeFuture;
}

下面来看看读数据的过程：

Java代码

public

final
CloseFuture close() {

synchronized
(lock) {

if
(isClosing()) {

return
closeFuture;

} else
{

closing = true
;

}

}

getFilterChain().fireFilterClose();//fire出关闭事件

return
closeFuture;

}

public

final
CloseFuture closeOnFlush() {

getWriteRequestQueue().offer(this
, CLOSE_REQUEST);

getProcessor().flush(this
);

return
closeFuture;

}

private
Queue<ReadFuture> getReadyReadFutures() {
//返回可被读数据队列

Queue<ReadFuture> readyReadFutures =

(Queue<ReadFuture>) getAttribute(READY_READ_FUTURES_KEY);//从会话映射表中取出可被读数据队列

if
(readyReadFutures ==
null
) {
//第一次读数据

readyReadFutures = new
CircularQueue<ReadFuture>();
//构造一个新读数据队列

Queue<ReadFuture> oldReadyReadFutures =

(Queue<ReadFuture>) setAttributeIfAbsent(

READY_READ_FUTURES_KEY, readyReadFutures);

if
(oldReadyReadFutures !=
null
) {

readyReadFutures = oldReadyReadFutures;

}

}

return
readyReadFutures;

}

public

final
ReadFuture read() {
//读数据

if
(!getConfig().isUseReadOperation()) {
//会话配置不允许读数据(这是默认情况)

throw

new
IllegalStateException(
"useReadOperation is not enabled."
);

}

Queue<ReadFuture> readyReadFutures = getReadyReadFutures();//获取已经可被读数据队列

ReadFuture future;

synchronized
(readyReadFutures) {
//锁住读数据队列

future = readyReadFutures.poll();//取队头数据

if
(future !=
null
) {

if
(future.isClosed()) {
//关联的会话已经关闭了，让读者知道此情况

readyReadFutures.offer(future);

}

} else
{

future = new
DefaultReadFuture(
this
);

getWaitingReadFutures().offer(future); //将此数据插入等待被读取数据的队列，这个代码和上面的getReadyReadFutures类似，只是键值不同而已

}

}

return
future;

}

public final CloseFuture close() {
synchronized (lock) {
if (isClosing()) {
return closeFuture;
} else {
closing = true;
}
}
getFilterChain().fireFilterClose();//fire出关闭事件
return closeFuture;
}

public final CloseFuture closeOnFlush() {
getWriteRequestQueue().offer(this, CLOSE_REQUEST);
getProcessor().flush(this);
return closeFuture;
}
private Queue<ReadFuture> getReadyReadFutures() {//返回可被读数据队列
Queue<ReadFuture> readyReadFutures =
(Queue<ReadFuture>) getAttribute(READY_READ_FUTURES_KEY);//从会话映射表中取出可被读数据队列
if (readyReadFutures == null) {//第一次读数据
readyReadFutures = new CircularQueue<ReadFuture>();//构造一个新读数据队列
Queue<ReadFuture> oldReadyReadFutures =
(Queue<ReadFuture>) setAttributeIfAbsent(
READY_READ_FUTURES_KEY, readyReadFutures);
if (oldReadyReadFutures != null) {
readyReadFutures = oldReadyReadFutures;
}
}
return readyReadFutures;
}

public final ReadFuture read() {//读数据
if (!getConfig().isUseReadOperation()) {//会话配置不允许读数据(这是默认情况)
throw new IllegalStateException("useReadOperation is not enabled.");
}
Queue<ReadFuture> readyReadFutures = getReadyReadFutures();//获取已经可被读数据队列
ReadFuture future;
synchronized (readyReadFutures) {//锁住读数据队列
future = readyReadFutures.poll();//取队头数据
if (future != null) {
if (future.isClosed()) {//关联的会话已经关闭了，让读者知道此情况
readyReadFutures.offer(future);
}
} else {
future = new DefaultReadFuture(this);
getWaitingReadFutures().offer(future); //将此数据插入等待被读取数据的队列，这个代码和上面的getReadyReadFutures类似，只是键值不同而已

}
}
return future;
}

再来看写数据到指定远端地址的过程，可以写三种类型数据：IoBuffer，整个文件或文件的部分区域，这会通过传递写请求给过滤器链条来完成数据向目的远端的传输。

Java代码

public

final
WriteFuture write(Object message, SocketAddress remoteAddress) {

FileChannel openedFileChannel = null
;

try

{

if
(message
instanceof
IoBuffer&& !((IoBuffer) message).hasRemaining())

{// 空消息

throw

new
IllegalArgumentException(

"message is empty. Forgot to call flip()?"
);

}

else

if
(message
instanceof
FileChannel)

{//要发送的是文件的某一区域

FileChannel fileChannel = (FileChannel) message;

message = new
DefaultFileRegion(fileChannel,
0
, fileChannel.size());

}

else

if
(message
instanceof
File)

{//要发送的是文件,打开文件通道

File file = (File) message;

openedFileChannel = new
FileInputStream(file).getChannel();

message = new
DefaultFileRegion(openedFileChannel,
0
, openedFileChannel.size());

}

}

catch
(IOException e)

{

ExceptionMonitor.getInstance().exceptionCaught(e);

return
DefaultWriteFuture.newNotWrittenFuture(
this
, e);

}

WriteFuture future = new
DefaultWriteFuture(
this
);

getFilterChain().fireFilterWrite(

new
DefaultWriteRequest(message, future, remoteAddress));
//构造写请求,通过过滤器链发送出去，写请求中指明了要发送的消息，目的地址，以及返回的结果

打开了一个文件通道（发送的文件的部分区域或全部），就必须在写请求完成时关闭文件通道

if
(openedFileChannel !=
null
) {

final
FileChannel finalChannel = openedFileChannel;

future.addListener(new
IoFutureListener<WriteFuture>() {

public

void
operationComplete(WriteFuture future) {

try
{

finalChannel.close();//关闭文件通道

} catch
(IOException e) {

ExceptionMonitor.getInstance().exceptionCaught(e);

}

}

});

}

return
future;
//写请求成功完成

}

public final WriteFuture write(Object message, SocketAddress remoteAddress) {
FileChannel openedFileChannel = null;
try
{
if (message instanceof IoBuffer&& !((IoBuffer) message).hasRemaining())
{// 空消息
throw new IllegalArgumentException(
"message is empty. Forgot to call flip()?");
}
else if (message instanceof FileChannel)
{//要发送的是文件的某一区域
FileChannel fileChannel = (FileChannel) message;
message = new DefaultFileRegion(fileChannel, 0, fileChannel.size());
}
else if (message instanceof File)
{//要发送的是文件,打开文件通道
File file = (File) message;
openedFileChannel = new FileInputStream(file).getChannel();
message = new DefaultFileRegion(openedFileChannel, 0, openedFileChannel.size());
}
}
catch (IOException e)
{
ExceptionMonitor.getInstance().exceptionCaught(e);
return DefaultWriteFuture.newNotWrittenFuture(this, e);
}
WriteFuture future = new DefaultWriteFuture(this);
getFilterChain().fireFilterWrite(
new DefaultWriteRequest(message, future, remoteAddress)); //构造写请求,通过过滤器链发送出去，写请求中指明了要发送的消息，目的地址，以及返回的结果

//如果打开了一个文件通道（发送的文件的部分区域或全部），就必须在写请求完成时关闭文件通道
if (openedFileChannel != null) {
final FileChannel finalChannel = openedFileChannel;
future.addListener(new IoFutureListener<WriteFuture>() {
public void operationComplete(WriteFuture future) {
try {
finalChannel.close();//关闭文件通道
} catch (IOException e) {
ExceptionMonitor.getInstance().exceptionCaught(e);
}
}
});
}
return future;//写请求成功完成
}

最后，来看看一个WriteRequestQueue的实现，唯一加入的一个功能就是若在队头发现是请求关闭，则会去关闭会话。

Java代码

private

class
CloseRequestAwareWriteRequestQueue
implements
WriteRequestQueue {

private

final
WriteRequestQueue q;
//内部实际的写请求队列

public
CloseRequestAwareWriteRequestQueue(WriteRequestQueue q) {

this
.q = q;

}

public

synchronized
WriteRequest poll(IoSession session) {

WriteRequest answer = q.poll(session);

if
(answer == CLOSE_REQUEST) {

AbstractIoSession.this
.close();

dispose(session);

answer = null
;

}

return
answer;

}

public

void
offer(IoSession session, WriteRequest e) {

q.offer(session, e);

}

public

boolean
isEmpty(IoSession session) {

return
q.isEmpty(session);

}

public

void
clear(IoSession session) {

q.clear(session);

}

public

void
dispose(IoSession session) {

q.dispose(session);

}

}