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【Java】NIO中Selector的select方法源码分析

2019-05-19 18:40 2041 查看

该篇博客的有些内容和在之前介绍过了,在这里再次涉及到的就不详细说了,如果有不理解请看【Java】NIO中Channel的注册源码分析【Java】NIO中Selector的创建源码分析

 

Selector的创建在Windows下默认生成WindowsSelectorImpl对象,那么Selector的select方法使用的就是WindowsSelectorImpl的select方法,而在WindowsSelectorImpl下并没有覆盖这个方法,而是由其基类SelectorImpl实现的:

public int select() throws IOException {
return this.select(0L);
}

这个方法调用了另一个重载的方法:

public int select(long var1) throws IOException {
if (var1 < 0L) {
throw new IllegalArgumentException("Negative timeout");
} else {
return this.lockAndDoSelect(var1 == 0L ? -1L : var1);
}
}

首先对var1参数的合法性进行判断,无参传入进来的是0,实则交给lockAndDoSelect方法去完成,并且令参数为-1。

private int lockAndDoSelect(long var1) throws IOException {
synchronized(this) {
if (!this.isOpen()) {
throw new ClosedSelectorException();
} else {
Set var4 = this.publicKeys;
int var10000;
synchronized(this.publicKeys) {
Set var5 = this.publicSelectedKeys;
synchronized(this.publicSelectedKeys) {
var10000 = this.doSelect(var1);
}
}

return var10000;
}
}
}

在方法执行时先使用同步块包裹,使用this作为锁;进入同步块先判断当前的Selector对象是否关闭了,因为在初始化时就是开启状态,只有在关闭后isOpen才是false;isOpen是由AbstractSelector实现的:

private AtomicBoolean selectorOpen = new AtomicBoolean(true);
public final boolean isOpen() {
return selectorOpen.get();
}
public final void close() throws IOException {
boolean open = selectorOpen.getAndSet(false);
if (!open)
return;
implCloseSelector();
}

可以看到在AbstractSelector中使用了原子化Boolean值表示开启关闭。

回到SelectorImpl的lockAndDoSelect,若是Selector已经关闭则抛出ClosedSelectorException异常,否则分别以publicKeys以及publicSelectedKeys为锁,最终的实现交给抽象方法doSelect完成;

protected abstract int doSelect(long var1) throws IOException;

其中publicKeys是供外部访问的SelectionKey集合,publicSelectedKeys是供外部访问并且已经就绪的SelectionKey集合。

因为使用的是WindowsSelectorImpl,所以来看看WindowsSelectorImpl的doSelect实现:

protected int doSelect(long var1) throws IOException {
if (this.channelArray == null) {
throw new ClosedSelectorException();
} else {
this.timeout = var1;
this.processDeregisterQueue();
if (this.interruptTriggered) {
this.resetWakeupSocket();
return 0;
} else {
this.adjustThreadsCount();
this.finishLock.reset();
this.startLock.startThreads();

try {
this.begin();

try {
this.subSelector.poll();
} catch (IOException var7) {
this.finishLock.setException(var7);
}

if (this.threads.size() > 0) {
this.finishLock.waitForHelperThreads();
}
} finally {
this.end();
}

this.finishLock.checkForException();
this.processDeregisterQueue();
int var3 = this.updateSelectedKeys();
this.resetWakeupSocket();
return var3;
}
}
}

首先判断channelArray是否为空,上一篇博客说了channelArray是一个SelectionKeyImpl数组,SelectionKeyImpl负责记录Channel和SelectionKey状态,channelArray是根据连接的Channel数量动态维持的,初始化大小是8。

private SelectionKeyImpl[] channelArray = new SelectionKeyImpl[8];

SelectionKeyImpl是SelectionKey的子类,只有当Selector调用close方法时,在回调函数中才会令channelArray=null,所以这还是检测Selector是否关闭了。
接着继续,在前面传入的long类型的参数是-1,在这里令超时时间timeout就等于-1,
接着调用processDeregisterQueue方法来取消准备撤销的集合
所谓的准备撤销的集合是因为SelectionKey对象在调用cancel方法时,会使Selector将其加入cancelledKeys,仅仅如此,真真的取消是在Selector调用selector方法时执行

SelectionKey的cancel方法是在AbstractSelectionKey中实现的:

public final void cancel() {
// Synchronizing "this" to prevent this key from getting canceled
// multiple times by different threads, which might cause race
// condition between selector's select() and channel's close().
synchronized (this) {
if (valid) {
valid = false;
((AbstractSelector)selector()).cancel(this);
}
}
}

这个方法在上一篇讲过,可以看到基本上什么都没做,仅仅时调用了与它关联的Selector对象(AbstractSelector)的cancel方法:
AbstractSelector的cancel方法:

private final Set<SelectionKey> cancelledKeys = new HashSet<SelectionKey>();

void cancel(SelectionKey k) {
synchronized (cancelledKeys) {
cancelledKeys.add(k);
}
}

cancelledKeys就是所谓的准备撤销的集合,可以看到AbstractSelector的cancel方法仅仅是把此时请求取消的SelectionKey对象加入到cancelledKeys集合中,并没有多余的操作。

回到doSelect方法,processDeregisterQueue这个方法的实现是在SelectorImpl中:

void processDeregisterQueue() throws IOException {
Set var1 = this.cancelledKeys();
synchronized(var1) {
if (!var1.isEmpty()) {
Iterator var3 = var1.iterator();

while(var3.hasNext()) {
SelectionKeyImpl var4 = (SelectionKeyImpl)var3.next();

try {
this.implDereg(var4);
} catch (SocketException var11) {
throw new IOException("Error deregistering key", var11);
} finally {
var3.remove();
}
}
}

}
}

这个方法的逻辑比较简单,首先得到准备撤销的集合cancelledKeys,判断是否有请求取消的,若有那么就进行遍历,实际的取消操作主要逻辑交给了抽象方法implDereg执行,最后再从集合中删除这个SelectionKeyImpl对象。

implDereg方法的实现是在WindowsSelectorImpl中:

protected void implDereg(SelectionKeyImpl var1) throws IOException {
int var2 = var1.getIndex();

assert var2 >= 0;

Object var3 = this.closeLock;
synchronized(this.closeLock) {
if (var2 != this.totalChannels - 1) {
SelectionKeyImpl var4 = this.channelArray[this.totalChannels - 1];
this.channelArray[var2] = var4;
var4.setIndex(var2);
this.pollWrapper.replaceEntry(this.pollWrapper, this.totalChannels - 1, this.pollWrapper, var2);
}

var1.setIndex(-1);
}

this.channelArray[this.totalChannels - 1] = null;
--this.totalChannels;
if (this.totalChannels != 1 && this.totalChannels % 1024 == 1) {
--this.totalChannels;
--this.threadsCount;
}

this.fdMap.remove(var1);
this.keys.remove(var1);
this.selectedKeys.remove(var1);
this.deregister(var1);
SelectableChannel var7 = var1.channel();
if (!var7.isOpen() && !var7.isRegistered()) {
((SelChImpl)var7).kill();
}

}

首先获取SelectionKeyImpl的下标Index,这个下标就是其在channelArray中的下标,检验下标的合法性;
在同步块内,首先检验这个SelectionKeyImpl对象是否是数组的最后一个元素,若不是那么就直接用最后一个元素覆盖当前位置的SelectionKeyImpl对象,同时还需要将pollWrapper中最后一个元素对应的Channel描述符和事件响应覆盖到相应位置。无论该SelectionKeyImpl对象是否是最后一个,都将其下标置为-1,防止再次访问。

再完成上述操作后,channelArray中的最后一个元素必然是不需要的,直接置为null,再totalChannels再自减。
接着根据totalChannels的数量来判断是否需要减少轮询线程的个数,这和注册时同理,就不再多说。
然后在fdMap中移除掉该SelectionKeyImpl和Channel的描述符映射(fdMap保存的是Channel的描述符和SelectionKeyImpl的映射关系,在上一篇提到过),keys和selectedKeys中同样也需要移除(keys所有注册了的SelectionKey集合,selectedKeys是所有有事件就绪的SelectionKey集合)。

这些操作仅仅是删除了其在Selector中的映射关系,而真正的Channel的(虽说是SelectionKey的cancel方法,实则是Channel要取消对某一事件的响应)取消操作是在deregister中执行:
deregister方法在AbstractSelector中实现:

protected final void deregister(AbstractSelectionKey key) {
((AbstractSelectableChannel)key.channel()).removeKey(key);
}

可以看到直接获取SelectionKey对应的channel对象,然后调用AbstractSelectableChannel的removeKey方法:

void removeKey(SelectionKey k) {
synchronized (keyLock) {
for (int i = 0; i < keys.length; i++)
if (keys[i] == k) {
keys[i] = null;
keyCount--;
}
((AbstractSelectionKey)k).invalidate();
}
}

前面的遍历很简单,通过遍历Channel的所有绑定的SelectionKey,即keys,直接将要取消的置为null,keyCount再自减,最后调用SelectionKey(AbstractSelectionKey)的invalidate方法:

void invalidate() {
valid = false;
}

直接设置valid属性为false,表明不可用。

回到implDereg中,最后一步操作,检查Channel的活跃性,若是Channel既没有打开且当且也没有注册了的SelectionKey,那么直接“杀死”该Channel。
而这个kill方法,在不同的Channel中有不同的实现,
SocketChannelImpl中:

public void kill() throws IOException {
Object var1 = this.stateLock;
synchronized(this.stateLock) {
if (this.state != 4) {
if (this.state == -1) {
this.state = 4;
} else {
assert !this.isOpen() && !this.isRegistered();

if (this.readerThread == 0L && this.writerThread == 0L) {
nd.close(this.fd);
this.state = 4;
} else {
this.state = 3;
}

}
}
}
}

其中state表示SocketChannelImpl的状态,一共有六种:

private static final int ST_UNINITIALIZED = -1;     // 尚未初始化
private static final int ST_UNCONNECTED = 0;         // 尚未建立连接
private static final int ST_PENDING = 1;              // 未决状态
private static final int ST_CONNECTED = 2;             // 连接状态
private static final int ST_KILLPENDING = 3;         // KILL的未决状态
private static final int ST_KILLED = 4;             // KILL状态
private int state = -1;

这样就很清晰,若是SocketChannelImpl尚未初始化直接变为KILL状态,否则检查再次检查Channel的活跃性,若是不活跃就断言为false,直接结束,否则“杀死”。
接下来的判断中的readerThread和writerThread,我在看完SocketChannelImpl后,发现一直都是赋值的0,并不知道会在何时发生修改,而且这两个成员的赋值都是在有数据读、写操作后,若是有知道的朋友想请教一下!
这个就先不讨论了,但是通过它们的赋值都是发生在有数据读、写操作后,那么就可以明白,若是完成了读、写,那么直接变为KILL状态,否则,等待读、写完成,就变为KILL的未决状态。
其中 nd.close(this.fd),nd是Socket描述符,fd是文件描述符,这就是由操作系统来关闭Socket描述符对应的文件描述符。

ServerSocketChannelImpl中kill:

private static final int ST_UNINITIALIZED = -1;      // 尚未初始化
private static final int ST_INUSE = 0;                 // 使用中
private static final int ST_KILLED = 1;             // KILL状态
private int state = -1;

public void kill() throws IOException {
Object var1 = this.stateLock;
synchronized(this.stateLock) {
if (this.state != 1) {
if (this.state == -1) {
this.state = 1;
} else {
assert !this.isOpen() && !this.isRegistered();

nd.close(this.fd);
this.state = 1;
}
}
}
}

ServerSocketChannelImpl就要简单一点,基本上一样,由于ServerSocketChannel只能注册ACCEPT事件响应,所以就没有判断读、写。

implDereg方法结束,processDeregisterQueue也彻底结束,再回到doSelect方法
接着检验interruptTriggered,表示是否触发中断。
interruptTriggered初始化时就是false,表示未触发中断,而在调用close或者wakeup方法时会触发中断,赋值true;

先看wakeup方法:

public Selector wakeup() {
Object var1 = this.interruptLock;
synchronized(this.interruptLock) {
if (!this.interruptTriggered) {
this.setWakeupSocket();
this.interruptTriggered = true;
}

return this;
}
}

可以看到核心是setWakeupSocket方法,当目前没有触发中断调用setWakeupSocket:

private void setWakeupSocket() {
this.setWakeupSocket0(this.wakeupSinkFd);
}
private native void setWakeupSocket0(int var1);

在讲Selector的创建时说过,在Selector创建时会产生一对SocketChannel,分别是SourceChannelImpl和SinkChannelImpl,wakeupSinkFd是SinkChannelImpl的描述符。

再来看看setWakeupSocket0的实现:

Java_sun_nio_ch_WindowsSelectorImpl_setWakeupSocket0(JNIEnv *env, jclass this,
jint scoutFd) {
/* Write one byte into the pipe */
const char byte = 1;
send(scoutFd, &byte, 1, 0);
}

虽然是用C写的,但是依旧很清晰,就是通过这个双向通道的sink端向source发送一个字节的数据,这样source端描述符就进入就绪状态,就能被select感知到,Selector便被唤醒。

再来看下close方法,在AbstractSelector中实现的:

public final void close() throws IOException {
boolean open = selectorOpen.getAndSet(false);
if (!open)
return;
implCloseSelector();
}

核心是implCloseSelector,在SelectorImpl中实现:

public void implCloseSelector() throws IOException {
this.wakeup();
synchronized(this) {
Set var2 = this.publicKeys;
synchronized(this.publicKeys) {
Set var3 = this.publicSelectedKeys;
synchronized(this.publicSelectedKeys) {
this.implClose();
}
}

}
}

一开始就直接调用wakeup方法唤醒,然后调用implClose方法:
implClose是在WindowsSelectorImpl中实现的:

protected void implClose() throws IOException {
Object var1 = this.closeLock;
synchronized(this.closeLock) {
if (this.channelArray != null && this.pollWrapper != null) {
Object var2 = this.interruptLock;
synchronized(this.interruptLock) {
this.interruptTriggered = true;
}

this.wakeupPipe.sink().close();
this.wakeupPipe.source().close();

for(int var7 = 1; var7 < this.totalChannels; ++var7) {
if (var7 % 1024 != 0) {
this.deregister(this.channelArray[var7]);
SelectableChannel var3 = this.channelArray[var7].channel();
if (!var3.isOpen() && !var3.isRegistered()) {
((SelChImpl)var3).kill();
}
}
}

this.pollWrapper.free();
this.pollWrapper = null;
this.selectedKeys = null;
this.channelArray = null;
Iterator var8 = this.threads.iterator();

while(var8.hasNext()) {
WindowsSelectorImpl.SelectThread var9 = (WindowsSelectorImpl.SelectThread)var8.next();
var9.makeZombie();
}

this.startLock.startThreads();
}

}
}

根据channelArray和pollWrapper是否为null来检验是否有必要关闭资源,后面就是对一些资源的关闭,可以看到关闭了我们一开始建立的双向通道,取消了所有注册事件,顺便“杀死”不活跃的Channel,删除所有映射关系,将所有轮询线程从阻塞中唤醒,关于makeZombie和startLock后面给出。

再次回到doSelect上,若是发生了中断,调用resetWakeupSocket方法恢复中断:

private void resetWakeupSocket() {
Object var1 = this.interruptLock;
synchronized(this.interruptLock) {
if (this.interruptTriggered) {
this.resetWakeupSocket0(this.wakeupSourceFd);
this.interruptTriggered = false;
}
}
}

resetWakeupSocket0也是一个native方法,和setWakeupSocket0正好互补,用来读取setWakeupSocket0中发送的数据,再将interruptTriggered设置为false,最后doSelect将会立即返回0,而不会调用poll操作。

在doSelect判断没有触发中断后,首先调用adjustThreadsCount调整轮询线程数量:

private void adjustThreadsCount() {
int var1;
if (this.threadsCount > this.threads.size()) {
for(var1 = this.threads.size(); var1 < this.threadsCount; ++var1) {
WindowsSelectorImpl.SelectThread var2 = new WindowsSelectorImpl.SelectThread(var1);
this.threads.add(var2);
var2.setDaemon(true);
var2.start();
}
} else if (this.threadsCount < this.threads.size()) {
for(var1 = this.threads.size() - 1; var1 >= this.threadsCount; --var1) {
((WindowsSelectorImpl.SelectThread)this.threads.remove(var1)).makeZombie();
}
}

}

threads是用ArrayList存放的:

private final List<WindowsSelectorImpl.SelectThread> threads = new ArrayList();

逻辑比较简单,通过检查threadsCount的数量和threads的大小比较,若是threadsCount大于threads,则产生一个新的轮询线程SelectThread,将其加入threads,并且设置轮询线程是守护线程,直接启动;若是threadsCount小于threads,则移除并唤醒多余的轮询线程;若是threadsCount等于threads什么都不做。

来看一下SelectThread这个轮询线程具体是怎么工作的:

private final class SelectThread extends Thread {
private final int index;
final WindowsSelectorImpl.SubSelector subSelector;
private long lastRun;
private volatile boolean zombie;

private SelectThread(int var2) {
this.lastRun = 0L;
this.index = var2;
this.subSelector = WindowsSelectorImpl.this.new SubSelector(var2);
this.lastRun = WindowsSelectorImpl.this.startLock.runsCounter;
}

void makeZombie() {
this.zombie = true;
}

boolean isZombie() {
return this.zombie;
}

public void run() {
for(; !WindowsSelectorImpl.this.startLock.waitForStart(this); WindowsSelectorImpl.this.finishLock.threadFinished()) {
try {
this.subSelector.poll(this.index);
} catch (IOException var2) {
WindowsSelectorImpl.this.finishLock.setException(var2);
}
}

}
}

在构造方法中对几个成员完成初始化,index对应的是其在ArrayList中的下标,lastRun 和startLock有关等会再说,subSelector是真正执行轮询的对象;zombie是一个标志,在startLock中会使用到。
再来看run方法,核心就是调用subSelector的poll方法,而何时调用该方法由startLock来决定。

StartLock的定义:

private final class StartLock {
private long runsCounter;

private StartLock() {
}

private synchronized void startThreads() {
++this.runsCounter;
this.notifyAll();
}

private synchronized boolean waitForStart(WindowsSelectorImpl.SelectThread var1) {
while(this.runsCounter == var1.lastRun) {
try {
WindowsSelectorImpl.this.startLock.wait();
} catch (InterruptedException var3) {
Thread.currentThread().interrupt();
}
}

if (var1.isZombie()) {
return true;
} else {
var1.lastRun = this.runsCounter;
return false;
}
}
}

在startThreads方法中,仅仅是通过synchronized 包裹,使runsCounter自增,然后notifyAll唤醒所有持有StartLock对象锁的阻塞。
在WindowsSelectorImpl中StartLock对象有且只有一份,对于所有SelectThread来说StartLock是公共的
waitForStart方法需要结合SelectThread的run方法来看,首先先检验SelectThread的lastRun成员是否和runsCounter相等,若是相等直接阻塞,等待startThreads方法将其唤醒;若是不相等,说明它的run是在startThreads之后运行的,需要将lastRun更新后再执行。

回到SelectThread中,我们再来看看SubSelector的定义:

private final class SubSelector {
private final int pollArrayIndex;
private final int[] readFds;
private final int[] writeFds;
private final int[] exceptFds;

private SubSelector() {
this.readFds = new int[1025];
this.writeFds = new int[1025];
this.exceptFds = new int[1025];
this.pollArrayIndex = 0;
}

private SubSelector(int var2) {
this.readFds = new int[1025];
this.writeFds = new int[1025];
this.exceptFds = new int[1025];
this.pollArrayIndex = (var2 + 1) * 1024;
}
......
}

其中无参构造是WindowsSelectorImpl使用的,单参构造由SelectThread使用。
之前在讲Channel的注册时说过,每1024个注册了的Channel会开启一个SelectThread轮询,如果是1024个以内,那么直接由WindowsSelectorImpl轮询,不交给SelectThread处理,超过1024则WindowsSelectorImpl和SelectThread一起轮询。

readFds 、writeFds、exceptFds 分别对应读、写、异常描述符 ,在SubSelector构造中初始化大小都是1025,多出来的一个就是前面说过的wakeupSourceFd描述符,用于唤醒,所以是1025。pollArrayIndex 对应其在pollWrapper中的wakeupSourceFd描述符的起始位置。

再来看看poll方法:

private int poll() throws IOException {
return this.poll0(WindowsSelectorImpl.this.pollWrapper.pollArrayAddress, Math.min(WindowsSelectorImpl.this.totalChannels, 1024), this.readFds, this.writeFds, this.exceptFds, WindowsSelectorImpl.this.timeout);
}

private int poll(int var1) throws IOException {
return this.poll0(WindowsSelectorImpl.this.pollWrapper.pollArrayAddress + (long)(this.pollArrayIndex * PollArrayWrapper.SIZE_POLLFD), Math.min(1024, WindowsSelectorImpl.this.totalChannels - (var1 + 1) * 1024), this.readFds, this.writeFds, this.exceptFds, WindowsSelectorImpl.this.timeout);
}

private native int poll0(long var1, int var3, int[] var4, int[] var5, int[] var6, long var7);

无参poll方法是WindowsSelectorImpl执行的,单参poll是由SelectThread执行;
最后都调用poll0这个native方法,这个方法是真正的轮询核心,交由操作系统来完成。
其中pollArrayAddress是pollArray在内存空间的起始位置,在poll()中直接定位到最开始,而在poll(int var1)中通过加上pollArrayIndex * PollArrayWrapper.SIZE_POLLFD这个偏移量定位。
PollArrayWrapper.SIZE_POLLFD是8,表示pollWrapper中存放的一对Channel描述符和事件响应共8位,0-3位保存Channel描述符fdVal,4-7位保存事件响应events。
第二个参数表明需要底层轮询的描述符fd个数,最后一个是超时时间,若是底层超时是会结束的。

还是回到doSelect方法,在adjustThreadsCount调整完轮询线程后,调用finishLock的reset方法
finishLock定义如下:

private final class FinishLock {
private int threadsToFinish;
IOException exception;

private FinishLock() {
this.exception = null;
}

private void reset() {
this.threadsToFinish = WindowsSelectorImpl.this.threads.size();
}

private synchronized void threadFinished() {
if (this.threadsToFinish == WindowsSelectorImpl.this.threads.size()) {
WindowsSelectorImpl.this.wakeup();
}

--this.threadsToFinish;
if (this.threadsToFinish == 0) {
this.notify();
}

}
......
}

这个和startLock很相似,也是WindowsSelectorImpl持有,有且仅有一份,所有SelectThread共享,reset方法用来记录在当前select方法执行时需要的轮询线程个数,在SelectThread的run方法中执行完poll方法后,会执行threadFinished,首先this.threadsToFinish == WindowsSelectorImpl.this.threads.size()的判断是为帮助唤醒所有处于poll阻塞的轮询。SelectThread执行完毕,就需要让threadsToFinish自减,至于notify的唤醒和后面有关系。

doSelect中执行完finishLock的reset后,就需要调用startLock的startThreads唤醒所有轮询线程工作。接着调用begin方法:
begin方法在AbstractSelector中实现:

private Interruptible interruptor = null;

protected final void begin() {
if (interruptor == null) {
interruptor = new Interruptible() {
public void interrupt(Thread ignore) {
AbstractSelector.this.wakeup();
}};
}
AbstractInterruptibleChannel.blockedOn(interruptor);
Thread me = Thread.currentThread();
if (me.isInterrupted())
interruptor.interrupt(me);
}

若是中断器interruptor=null,就创建一个,当当前线程阻塞在I/O操作上并且发生了线程级别的中断时,就会调用wakeup方法唤醒Selector。

doSelect中begin完毕后,调用subSelector的poll方法轮询;若是poll上有事件就绪,那么就不会阻塞,继续往下进行;若poll上没有事件就绪就会等待SelectThread上的事件就绪,通过threadFinished将其唤醒;若是SelectThread上也没有事件就绪就会一直阻塞,除非被外部唤醒,或者调用的是select的单参方法,会阻塞到超时结束。

接着判断是否有轮询线程的工作,调用waitForHelperThreads等待轮询线程的结束:

private synchronized void waitForHelperThreads() {
if (this.threadsToFinish == WindowsSelectorImpl.this.threads.size() {
WindowsSelectorImpl.this.wakeup();
}

while(this.threadsToFinish != 0) {
try {
WindowsSelectorImpl.this.finishLock.wait();
} catch (InterruptedException var2) {
Thread.currentThread().interrupt();
}
}

}

waitForHelperThreads方法就呼应了threadFinished方法,若是threadsToFinish != 0说明还有轮询线程没有结束,就wait阻塞,一直等到threadsToFinish == 0时再将其唤醒。

当所有轮询结束后,调用end方法:

protected final void end() {
AbstractInterruptibleChannel.blockedOn(null);
}

这个方法是处理发生中断,具体就不详细介绍了。

然后调用finishLock的checkForException方法检查异常,这个没啥好说的,然后又调用processDeregisterQueue来取消可能在select轮询时发生的SelectionKeyl的撤销。

接着调用updateSelectedKeys方法:

private long updateCount = 0L;

private int updateSelectedKeys() {
++this.updateCount;
byte var1 = 0;
int var4 = var1 + this.subSelector.processSelectedKeys(this.updateCount);

WindowsSelectorImpl.SelectThread var3;
for(Iterator var2 = this.threads.iterator(); var2.hasNext(); var4 += var3.subSelector.processSelectedKeys(this.updateCount)) {
var3 = (WindowsSelectorImpl.SelectThread)var2.next();
}

return var4;
}

updateCount记录更新次数,即select调用次数;然后调用subSelector的processSelectedKeys方法,得到poll返回的就绪的Channel描述符,也就是得到事件就绪的Channel个数,同理也就需要得到所有SelectThread中的。

其中processSelectedKeys方法如下:

private int processSelectedKeys(long var1) {
byte var3 = 0;
int var4 = var3 + this.processFDSet(var1, this.readFds, Net.POLLIN, false);
var4 += this.processFDSet(var1, this.writeFds, Net.POLLCONN | Net.POLLOUT, false);
var4 += this.processFDSet(var1, this.exceptFds, Net.POLLIN | Net.POLLCONN | Net.POLLOUT, true);
return var4;
}

分别对读、写、异常都处理了,主要还是调用processFDSet方法:

private int processFDSet(long var1, int[] var3, int var4, boolean var5) {
int var6 = 0;

for(int var7 = 1; var7 <= var3[0]; ++var7) {
int var8 = var3[var7];
if (var8 == WindowsSelectorImpl.this.wakeupSourceFd) {
synchronized(WindowsSelectorImpl.this.interruptLock) {
WindowsSelectorImpl.this.interruptTriggered = true;
}
} else {
WindowsSelectorImpl.MapEntry var9 = WindowsSelectorImpl.this.fdMap.get(var8);
if (var9 != null) {
SelectionKeyImpl var10 = var9.ski;
if (!var5 || !(var10.channel() instanceof SocketChannelImpl) || !WindowsSelectorImpl.this.discardUrgentData(var8)) {
if (WindowsSelectorImpl.this.selectedKeys.contains(var10)) {
if (var9.clearedCount != var1) {
if (var10.channel.translateAndSetReadyOps(var4, var10) && var9.updateCount != var1) {
var9.updateCount = var1;
++var6;
}
} else if (var10.channel.translateAndUpdateReadyOps(var4, var10) && var9.updateCount != var1) {
var9.updateCount = var1;
++var6;
}

var9.clearedCount = var1;
} else {
if (var9.clearedCount != var1) {
var10.channel.translateAndSetReadyOps(var4, var10);
if ((var10.nioReadyOps() & var10.nioInterestOps()) != 0) {
WindowsSelectorImpl.this.selectedKeys.add(var10);
var9.updateCount = var1;
++var6;
}
} else {
var10.channel.translateAndUpdateReadyOps(var4, var10);
if ((var10.nioReadyOps() & var10.nioInterestOps()) != 0) {
WindowsSelectorImpl.this.selectedKeys.add(var10);
var9.updateCount = var1;
++var6;
}
}

var9.clearedCount = var1;
}
}
}
}
}

return var6;
}

这个方法其实就是把poll0方法轮询的描述符结果放入传入的数组中,然后通过遍历这个数组,得到相应的Channel描述符,因为之前通过fdMap保存了Channel的描述符和SelectionKeyImpl的映射关系,那么就可以根据Channel描述符找到对应的SelectionKeyImpl对象,再根据传入的状态值var4来更新Channel的状态,最后将其保存在selectedKeys集合中供外部访问。


Selector的select方法到此全部结束。

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