3. Java NIO之Selector如何实现（三）

Selector默认是WindowsSelectorImpl的一个实例，
当调用了SelectorImpl的select()方法的时候，调用selector(timeout)，之后会调用lockAndDoSelect()，在这个方法中，主要调用了doSelect()方法，参数与传进来的一致，以WindowsSelectorImpl为例子，实现的doSelect()方法。

    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;
            }
        }
    }

首先调用processD额registerQueue()方法，从而将已经准备注销注册的channel进行注销注册。

    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();
                    }
                }
            }
 
        }
    }

遍历取得所有要注销注册的SelectionKey（加到cancelledKeys中的SelectionKey），并且依次调用implDereg()进行注销绑定。

    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();
        }
 
    }

这里如果需要注销操作的channel已经是selector中最后一个了，那么直接从数组中移除。
否则，则需要将当前需要移除的channel与数组最后一个channel进行位置交换，保证数组中间位置连续，再移除。
之后操作即就是对注册操作的反向操作。

完成真正注销后，调用adjustThreadCount()来调整线程的数量：

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();
        }
    }
 
}

在Selector中，每1024条channel就需要重新打开一个线程加入进行监听的操作，这里，重新根据当前应该有的线程数量与此时现存的线程数量进行比较，进行动态调整。
在此之后，调用begin()方法，准备开始正式进行select操作。

    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);
    }

begin()方法判断这里interruptor是否为空，如果为空，则会在这里重新生成一个。
这里的Interruptor保证了当线程阻塞在io操作上，并且被interruptor时，保证selector能够被唤醒。

在begin()方法执行完毕后，将会调用其subSelector的poll()方法，正式开始select操作。

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);

这里poll0()是native方法（原生方法的实现），主要为了监听pollWrapper中保存的fd是否有数据进出，如果没有进出，那么此处在timeout时间里一直保持阻塞状态。

数据监听完成后取得相应数据，在此之后将重新检验一边已经取消注册的channel，进行注销。之后调用updateSelectedKeys()方法。

    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;
    }

这里对所有的线程调用processSelectedKeys来处理所有线程在poll过程中取得的结果进行处理，然后返回所以线程中处理的channel数量的总和。
接下来看processSelectedKeys()方法：

private int processSelectedKeys(long var1) {
    byte var3 = 0;
    int var4 = var3 + this.processFDSet(var1, this.readFds, 1, false);
    var4 += this.processFDSet(var1, this.writeFds, 6, false);
    var4 += this.processFDSet(var1, this.exceptFds, 7, true);
    return var4;
}
 
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;
}

这里主要对之前监听到的发生io事件需要处理的fd与对应的channel进行操作，根据读取到的fd取得selector下注册了的相应的channel，根据监听到其所发生事件类型（读、写、异常），从而更新channel应该的状态。
在此操作之后，相应的selector的select也相应完成。