Selector

Selector

之前说过  SingleThreadEventExecutor.this.run(); 方法，里面有段代码  strategy = selectStrategy.calculateStrategy(selectNowSupplier, hasTasks());

现在详细说明下此方法

@Override
    public int calculateStrategy(IntSupplier selectSupplier, boolean hasTasks) throws Exception {
        return hasTasks ? selectSupplier.get() : SelectStrategy.SELECT;
    }

如果当前 NioEventLoop 线程存在异步任务，会通过 selectSupplier.get() 最终调用到 selectNow() 方法，selectNow() 是非阻塞，执行后立即返回0。跳出switch，直接执行后续代码。

如果当前 NioEventLoop 线程不存在异步任务，会调用 SelectStrategy.SELECT 立即返回-1。进入case SelectStrategy.SELECT 代码块。

刚开始，hasTasks 为true，因为 AbstractChannel#register 方法中会提交异步任务。

 SingleThreadEventExecutor#execute(Runnable task)

 所有一开始执行selectNow()。

select(curDeadlineNanos)

private int select(long deadlineNanos) throws IOException {
        if (deadlineNanos == NONE) {
            return selector.select();
        }
        // Timeout will only be 0 if deadline is within 5 microsecs
        long timeoutMillis = deadlineToDelayNanos(deadlineNanos + 995000L) / 1000000L;
        return timeoutMillis <= 0 ? selector.selectNow() : selector.select(timeoutMillis);
    }

SelectorImpl#select()

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

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

selectNow()

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

可见，selectNow 也是调用 lockAndDoSelect 方法。区别在于 selectNow() 方法中 lockAndDoSelect 方法参数为0，select() 方法中 lockAndDoSelect 方法参数为-1。

SelectorImpl#lockAndDoSelect(long var1)

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

                return var10000;
            }
        }
    }

最终会调用sun.nio.ch.WindowsSelectorImpl#doSelect 方法


protected int doSelect(long var1) throws IOException {
        if (this.channelArray == null) {
            throw new ClosedSelectorException();
        } else {
            this.timeout = var1;
            this.processDeregisterQueue();//如果key取消了，就要从队列中注销
            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();//再次注销队列
                int var3 = this.updateSelectedKeys();//更新并处理key
                this.resetWakeupSocket();
                return var3;
            }
        }
    }

processDeregisterQueue()

把一些出现异常而取消的key删除：

void processDeregisterQueue() throws IOException {
        Set var1 = this.cancelledKeys();//获取已经取消的keys
        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();
                    }
                }
            }

        }
    }

implDereg

执行选择中注销操作

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

        assert var2 >= 0;

        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);//从选择器key集合里删除
        this.selectedKeys.remove(var1);//删除要操作的key
        this.deregister(var1);//从通道中删除key
        SelectableChannel var3 = var1.channel();
        if (!var3.isOpen() && !var3.isRegistered()) {
            ((SelChImpl)var3).kill();//关闭通道
        }

    }

subSelector.poll()

这底层就是native方法

updateSelectedKeys()

返回之后的处理工作，看看有没有事件

 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;
    }

processSelectedKeys(long var1)

处理读写异常三个集合的事件

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;
        }

processFDSet

主要的就是下面的处理，会把放进去的集合遍历一遍，取出相应的事件key，检查触发的事件是否是感兴趣的事件，是就会加入selectedKeys，这个也是我们后面要去遍历的集合。

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;//取出key
                        if (!var5 || !(var10.channel() instanceof SocketChannelImpl) || !WindowsSelectorImpl.this.discardUrgentData(var8)) {
                            if (WindowsSelectorImpl.this.selectedKeys.contains(var10)) {//判断事件集合是否已包含此事件
                                if (var9.clearedCount != var1) {
                                    if (var10.channel.translateAndSetReadyOps(var4, var10) && var9.updateCount != var1) {
                                        var9.updateCount = var1;//更新数量
                                        ++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;
        }

WindowsSelectorImpl.this.selectedKeys.add(var10)

即SelectedSelectionKeySet#add 方法

public boolean add(SelectionKey o) {
        if (o == null) {
            return false;
        }

        keys[size++] = o;
        if (size == keys.length) {
            increaseCapacity();
        }

        return true;
    }

调用链路

而这个SelectedSelectionKeySet在哪里调用呢？在 run 方法的 processSelectedKeys(); 中调用 processSelectedKeysOptimized(); 方法时，会遍历selectedKeys 集合。取出之前add的SelectionKeyImpl 并做响应的处理。

 至此完成。

AbstractNioChannel#doRegister()

注册监听连接事件，

 protected void doRegister() throws Exception {
        boolean selected = false;
        for (;;) {
            try {
                selectionKey = javaChannel().register(eventLoop().unwrappedSelector(), 0, this);
                return;
            } catch (CancelledKeyException e) {
                if (!selected) {
                    // Force the Selector to select now as the "canceled" SelectionKey may still be
                    // cached and not removed because no Select.select(..) operation was called yet.
                    eventLoop().selectNow();
                    selected = true;
                } else {
                    // We forced a select operation on the selector before but the SelectionKey is still cached
                    // for whatever reason. JDK bug ?
                    throw e;
                }
            }
        }
    }

java.nio.channels.spi.AbstractSelectableChannel#register

public final SelectionKey register(Selector sel, int ops,
                                       Object att)
        throws ClosedChannelException
    {
        synchronized (regLock) {//注册锁
            if (!isOpen())//验证通道否打开
                throw new ClosedChannelException();
            if ((ops & ~validOps()) != 0)//验证参数
                throw new IllegalArgumentException();
            if (blocking)//判断是否非阻塞模式
                throw new IllegalBlockingModeException();
            SelectionKey k = findKey(sel);//是否有注册过key
            if (k != null) {//有的话就设置下感兴趣事件和附件
                k.interestOps(ops);
                k.attach(att);
            }
            if (k == null) {
                // New registration
                synchronized (keyLock) {//key锁
                    if (!isOpen())
                        throw new ClosedChannelException();
                    k = ((AbstractSelector)sel).register(this, ops, att);//没有就注册下
                    addKey(k);//保存key，便于通道关闭的时候取消注册
                }
            }
            return k;
        }
    }

findKey(Selector sel)

获得当前通道中的key的选择器与传入选择器相同的key：

private SelectionKey findKey(Selector sel) {
        synchronized (keyLock) {
            if (keys == null)
                return null;
            for (int i = 0; i < keys.length; i++)
                if ((keys[i] != null) && (keys[i].selector() == sel))//存在且选择器相同
                    return keys[i];
            return null;
        }
    }

register(AbstractSelectableChannel ch, int ops, Object attachment)

选择器注册key，sun.nio.ch.SelectorImpl的register：

protected final SelectionKey register(AbstractSelectableChannel var1, int var2, Object var3) {
        if (!(var1 instanceof SelChImpl)) {
            throw new IllegalSelectorException();
        } else {
            SelectionKeyImpl var4 = new SelectionKeyImpl((SelChImpl)var1, this);//创建一个实现类
            var4.attach(var3);
            synchronized(this.publicKeys) {
                this.implRegister(var4);//注册进选择器队列
            }

            var4.interestOps(var2);
            return var4;
        }
    }

implRegister(SelectionKeyImpl var1)

protected void implRegister(SelectionKeyImpl var1) {
        synchronized(this.closeLock) {
            if (this.pollWrapper == null) {
                throw new ClosedSelectorException();
            } else {
                this.growIfNeeded();
                this.channelArray[this.totalChannels] = var1;
                var1.setIndex(this.totalChannels);
                this.fdMap.put(var1);
                this.keys.add(var1);//保存key
                this.pollWrapper.addEntry(this.totalChannels, var1);
                ++this.totalChannels;
            }
        }
    }

addKey(SelectionKey k)

private void addKey(SelectionKey k) {
        assert Thread.holdsLock(keyLock);
        int i = 0;
        if ((keys != null) && (keyCount < keys.length)) {
            // Find empty element of key array
            for (i = 0; i < keys.length; i++)
                if (keys[i] == null)
                    break;
        } else if (keys == null) {
            keys =  new SelectionKey[3];
        } else {
            // Grow key array
            int n = keys.length * 2;
            SelectionKey[] ks =  new SelectionKey[n];
            for (i = 0; i < keys.length; i++)
                ks[i] = keys[i];
            keys = ks;
            i = keyCount;
        }
        keys[i] = k;
        keyCount++;
    }

keys即是前文提到的 AbstractSelectableChannel#register方法中的 findkey(sel)。这样就关联起来了，这边加，那边取，形成闭环。