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最新推荐文章于 2025-09-11 23:12:53 发布

转载最新推荐文章于 2025-09-11 23:12:53 发布 · 91 阅读

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原文链接：https://my.oschina.net/huangweiindex/blog/2253652

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#epoll #java #python

2019独角兽企业重金招聘Python工程师标准>>>

举例说明下 selecter

场景:线上服务报警系统

注册 channel(套接字)

see /Users/hanjun/Downloads/jdk_src2/sun/nio/ch/SelectorImpl.java

 protected final SelectionKey register(AbstractSelectableChannel ch,
                                          int ops,
                                          Object attachment)
    {
        if (!(ch instanceof SelChImpl))
            throw new IllegalSelectorException();
        SelectionKeyImpl k = new SelectionKeyImpl((SelChImpl)ch, this);
        k.attach(attachment);
        synchronized (publicKeys) {
            implRegister(k);
        }
        k.interestOps(ops);
        return k;
    }

其中,

implRegister(k) 是为了写入 channel 文件描述符的位置;
k.interestOps(ops) 为了写入监听的channel 可处理的操作

ops 的取值

SelectionKey.OP_CONNECT
SelectionKey.OP_WRITE
SelectionKey.OP_READ

implRegister的实现

见/Users/whuanghkl/Downloads/rt.jar.source/classes/sun/nio/ch/AbstractPollSelectorImpl.java

  protected void implRegister(SelectionKeyImpl ski) {
        synchronized (closeLock) {
            if (closed)
                throw new ClosedSelectorException();

            // Check to see if the array is large enough
            if (channelArray.length == totalChannels) {
                // Make a larger array
                int newSize = pollWrapper.totalChannels * 2;
                SelectionKeyImpl temp[] = new SelectionKeyImpl[newSize];
                // Copy over
                for (int i=channelOffset; i<totalChannels; i++)
                    temp[i] = channelArray[i];
                channelArray = temp;
                // Grow the NativeObject poll array
                pollWrapper.grow(newSize);
            }
            channelArray[totalChannels] = ski;
            ski.setIndex(totalChannels);
            pollWrapper.addEntry(ski.channel);
            totalChannels++;
            keys.add(ski);
        }
    }
	
	
    void addEntry(SelChImpl var1) {
        this.putDescriptor(this.totalChannels, IOUtil.fdVal(var1.getFD()));
        this.putEventOps(this.totalChannels, 0);
        this.putReventOps(this.totalChannels, 0);
        ++this.totalChannels;
    }

Windows 实现

见 /Users/hanjun/Downloads/openjdk-8u40-src-b25-10_feb_2015/openjdk/jdk/src/windows/classes/sun/nio/ch/WindowsSelectorImpl.java


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

重点方法: pollWrapper.addEntry(totalChannels, ski);

 void addEntry(SelChImpl var1) {
        this.putDescriptor(this.totalChannels, IOUtil.fdVal(var1.getFD()));
        this.putEventOps(this.totalChannels, 0);
        this.putReventOps(this.totalChannels, 0);
        ++this.totalChannels;
    }

注册(监听)channel感兴趣的操作

k.interestOps(ops)

public SelectionKey interestOps(int ops) {
        ensureValid();
        return nioInterestOps(ops);
    }
	
	public SelectionKey nioInterestOps(int ops) {
        if ((ops & ~channel().validOps()) != 0)
            throw new IllegalArgumentException();
        channel.translateAndSetInterestOps(ops, this);
        interestOps = ops;
        return this;
    }

方法channel.translateAndSetInterestOps(ops, this)中调用了 void translateAndSetInterestOps(int ops, SelectionKeyImpl sk);

translateAndSetInterestOps 见/Users/hanjun/Downloads/jdk_src2/sun/nio/ch/SocketChannelImpl.java

 /**
     * Translates an interest operation set into a native poll event set
     */
    public void translateAndSetInterestOps(int ops, SelectionKeyImpl sk) {
        int newOps = 0;
        if ((ops & SelectionKey.OP_READ) != 0)
            newOps |= Net.POLLIN;
        if ((ops & SelectionKey.OP_WRITE) != 0)
            newOps |= Net.POLLOUT;
        if ((ops & SelectionKey.OP_CONNECT) != 0)
            newOps |= Net.POLLCONN;
        sk.selector.putEventOps(sk, newOps);
    }

/Users/hanjun/Downloads/jdk_src2/sun/nio/ch/AbstractPollSelectorImpl.java 中

 public void putEventOps(SelectionKeyImpl sk, int ops) {
        synchronized (closeLock) {
            if (closed)
                throw new ClosedSelectorException();
            pollWrapper.putEventOps(sk.getIndex(), ops);
        }
    }

  void putEventOps(int i, int event) {
        int offset = SIZE_POLLFD * i + EVENT_OFFSET;
        pollArray.putShort(offset, (short)event);
    }

unsafe 常用操作解析

putInt 表示在指定位置写入一个 int类型数据

 /**
     * Writes an int at the specified offset from this native object's
     * base address.
     *
     * @param  offset
     *         The offset at which to write the int
     *
     * @param  value
     *         The int value to be written
     */
    final void putInt(int offset, int value) {
        unsafe.putInt(offset + address, value);
    }

poll

见 /Users/hanjun/Downloads/openjdk-8u40-src-b25-10_feb_2015/openjdk/jdk/src/windows/classes/sun/nio/ch/WindowsSelectorImpl.java

        private int poll() throws IOException{ // poll for the main thread
            return poll0(pollWrapper.pollArrayAddress,
                         Math.min(totalChannels, MAX_SELECTABLE_FDS),
                         readFds, writeFds, exceptFds, timeout);
        }

        private int poll(int index) throws IOException {
            // poll for helper threads
            return  poll0(pollWrapper.pollArrayAddress +
                     (pollArrayIndex * PollArrayWrapper.SIZE_POLLFD),
                     Math.min(MAX_SELECTABLE_FDS,
                             totalChannels - (index + 1) * MAX_SELECTABLE_FDS),
                     readFds, writeFds, exceptFds, timeout);
        }

调用操作系统的能力来监听socket

select

select做了哪些事?

poll,阻塞,获取channel 列表中可操作的channel;
如果有可以操作的channel,则poll 会返回;
根据操作系统调用的返回readFds, writeFds, exceptFds,来更新selectedKeys 见 /Users/hanjun/Downloads/jdk_src2/sun/nio/ch/AbstractPollSelectorImpl.java

    /**
     * Copy the information in the pollfd structs into the opss
     * of the corresponding Channels. Add the ready keys to the
     * ready queue.
     */
    protected int updateSelectedKeys() {
        int numKeysUpdated = 0;
        // Skip zeroth entry; it is for interrupts only
        for (int i=channelOffset; i<totalChannels; i++) {
            int rOps = pollWrapper.getReventOps(i);
            if (rOps != 0) {
                SelectionKeyImpl sk = channelArray[i];
                pollWrapper.putReventOps(i, 0);
                if (selectedKeys.contains(sk)) {
                    if (sk.channel.translateAndSetReadyOps(rOps, sk)) {
                        numKeysUpdated++;
                    }
                } else {
                    sk.channel.translateAndSetReadyOps(rOps, sk);
                    if ((sk.nioReadyOps() & sk.nioInterestOps()) != 0) {
                        selectedKeys.add(sk);
                        numKeysUpdated++;
                    }
                }
            }
        }
        return numKeysUpdated;
    }

处理监听结果

见 /Users/hanjun/Downloads/openjdk-8u40-src-b25-10_feb_2015/openjdk/jdk/src/windows/classes/sun/nio/ch/WindowsSelectorImpl.java


        private int processSelectedKeys(long updateCount) {
            int numKeysUpdated = 0;
            numKeysUpdated += processFDSet(updateCount, readFds,
                                           Net.POLLIN,
                                           false);
            numKeysUpdated += processFDSet(updateCount, writeFds,
                                           Net.POLLCONN |
                                           Net.POLLOUT,
                                           false);
            numKeysUpdated += processFDSet(updateCount, exceptFds,
                                           Net.POLLIN |
                                           Net.POLLCONN |
                                           Net.POLLOUT,
                                           true);
            return numKeysUpdated;
        }

AbstractPollArrayWrapper 源码

/**
 * Manipulates a native array of pollfd structs.
 *
 * @author Mike McCloskey
 * @since 1.4
 */

public abstract class AbstractPollArrayWrapper {

    // Miscellaneous constants
    static final short SIZE_POLLFD   = 8;
    static final short FD_OFFSET     = 0;
    static final short EVENT_OFFSET  = 4;
    static final short REVENT_OFFSET = 6;

    // The poll fd array
    protected AllocatedNativeObject pollArray;

    // Number of valid entries in the pollArray
    protected int totalChannels = 0;

    // Base address of the native pollArray
    protected long pollArrayAddress;

    // Access methods for fd structures
    int getEventOps(int i) {
        int offset = SIZE_POLLFD * i + EVENT_OFFSET;
        return pollArray.getShort(offset);
    }

    int getReventOps(int i) {
        int offset = SIZE_POLLFD * i + REVENT_OFFSET;
        return pollArray.getShort(offset);
    }

    int getDescriptor(int i) {
        int offset = SIZE_POLLFD * i + FD_OFFSET;
        return pollArray.getInt(offset);
    }

    void putEventOps(int i, int event) {
        int offset = SIZE_POLLFD * i + EVENT_OFFSET;
        pollArray.putShort(offset, (short)event);
    }

    void putReventOps(int i, int revent) {
        int offset = SIZE_POLLFD * i + REVENT_OFFSET;
        pollArray.putShort(offset, (short)revent);
    }

    void putDescriptor(int i, int fd) {
        int offset = SIZE_POLLFD * i + FD_OFFSET;
        pollArray.putInt(offset, fd);
    }

}

int 是四个字节

见/Users/hanjun/Downloads/jdk_src2/sun/nio/ch/NativeObject.java


  /**
     * Reads an address from this native object at the given offset and
     * constructs a native object using that address.
     *
     * @param  offset
     *         The offset of the address to be read.  Note that the size of an
     *         address is implementation-dependent.
     *
     * @return The native object created using the address read from the
     *         given offset
     */
    NativeObject getObject(int offset) {
        long newAddress = 0L;
        switch (addressSize()) {
            case 8:
                newAddress = unsafe.getLong(offset + address);
                break;
            case 4:
                newAddress = unsafe.getInt(offset + address) & 0x00000000FFFFFFFF;
                break;
            default:
                throw new InternalError("Address size not supported");
        }

        return new NativeObject(newAddress);
    }

poll file description 的结构

见 /Users/hanjun/Downloads/jdk_src2/sun/nio/ch/PollArrayWrapper.java

Manipulates a native array of pollfd structs on Solaris:
 
  typedef struct pollfd {
     int fd;
    short events;
     short revents;
  } pollfd_t;

一个描述符占用8个字节

jdk源码

https://yddmax.github.io/2017/06/05/openjdk%E6%BA%90%E7%A0%81%E7%9B%AE%E5%BD%95/

转载于:https://my.oschina.net/huangweiindex/blog/2253652