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关于nio:NIO源码JavaNIO源码-JNI分析二Java-NIO源码分析

没看过的倡议先看上一篇,原本打算讲讲 linux 内核,也看了一些书籍,可是 c 放了太久了,看代码切实头疼,就先放弃了,写写业务也没必要卷这么深吧。就讲到调用底层 api 为止我感觉刚刚好。不太善于将源码联合讲故事,所以整片略显干燥,将就看下吧~~

demo

public class ServerConnect
{public static void main(String[] args)
    {selector();
    }
    public static void handleAccept(SelectionKey key) throws IOException{ServerSocketChannel ssChannel = (ServerSocketChannel)key.channel();
        SocketChannel sc = ssChannel.accept();
        sc.configureBlocking(false);
        sc.register(key.selector(), SelectionKey.OP_READ,ByteBuffer.allocateDirect(1024));
    }
    public static void handleRead(SelectionKey key) throws IOException{SocketChannel sc = (SocketChannel)key.channel();
        ByteBuffer buf = (ByteBuffer)key.attachment();
        long bytesRead = sc.read(buf);
        while(bytesRead>0){buf.flip();
            while(buf.hasRemaining()){System.out.print((char)buf.get());
            }
            buf.clear();
            bytesRead = sc.read(buf);
        }
        if(bytesRead == -1){sc.close();
        }
    }
    public static void handleWrite(SelectionKey key) throws IOException{ByteBuffer buf = (ByteBuffer)key.attachment();
        buf.flip();
        SocketChannel sc = (SocketChannel) key.channel();
        while(buf.hasRemaining()){sc.write(buf);
        }
        buf.compact();}
    public static void selector() {
        Selector selector = null;
        ServerSocketChannel ssc = null;
        try{selector = Selector.open();
            ssc= ServerSocketChannel.open();
            ssc.socket().bind(new InetSocketAddress(8080));
            ssc.configureBlocking(false);
            ssc.register(selector, SelectionKey.OP_ACCEPT);
            while(true){if(selector.select(3000) == 0){continue;}
                Iterator<SelectionKey> iter = selector.selectedKeys().iterator();
                while(iter.hasNext()){SelectionKey key = iter.next();
                    if(key.isAcceptable()){handleAccept(key);
                    }
                    if(key.isReadable()){handleRead(key);
                    }
                    if(key.isWritable() && key.isValid()){handleWrite(key);
                    }
                    if(key.isConnectable()){System.out.println("isConnectable = true");
                    }
                    iter.remove();}
            }
        }catch(IOException e){e.printStackTrace();
        }finally{
            try{if(selector!=null){selector.close();
                }
                if(ssc!=null){ssc.close();
                }
            }catch(IOException e){e.printStackTrace();
            }
        }
    }
}

源码剖析

Selector.open()

此处会有 SelectorProvider 是个模板办法,不必零碎的实现不同,这就很蛋疼,没有EPollSelectorProvider,莫的方法,只能去 github 找了一份源码迁徙到 gitee,jdk8 感兴趣的能够自行下载,想看其余版本的同学就要自行寻找了。

EPollSelectorImpl(SelectorProvider sp) throws IOException {super(sp);
    long pipeFds = IOUtil.makePipe(false);
    fd0 = (int) (pipeFds >>> 32);
    fd1 = (int) pipeFds;
    pollWrapper = new EPollArrayWrapper();
    pollWrapper.initInterrupt(fd0, fd1);
    fdToKey = new HashMap<>();}

IOUtil.makePipe(false)

IOUtil.makePipe(false);是一个 JNI 办法对应的门路为/jdk8u_jdk/src/solaris/native/sun/nio/ch/IOUtil.c

  • 底层会调用int pipe(int pipefd[2]);
  • 函数 pipe()会建设管道,并将文件形容词由参数 pipefd 数组返回。

    • pipefd[0]为管道里的读取端
    • pipefd[1]则为管道的写入端
JNIEXPORT jlong JNICALL
Java_sun_nio_ch_IOUtil_makePipe(JNIEnv *env, jobject this, jboolean blocking)
{int fd[2];
        // 调用 pipe 函数
    if (pipe(fd) < 0) {JNU_ThrowIOExceptionWithLastError(env, "Pipe failed");
        return 0;
    }
    if (blocking == JNI_FALSE) {if ((configureBlocking(fd[0], JNI_FALSE) < 0)
            || (configureBlocking(fd[1], JNI_FALSE) < 0)) {JNU_ThrowIOExceptionWithLastError(env, "Configure blocking failed");
            close(fd[0]);
            close(fd[1]);
            return 0;
        }
    }
    // 2 个地址合并成 long 返回
    return ((jlong) fd[0] << 32) | (jlong) fd[1];
}

new EPollArrayWrapper()

这个类呢,类正文写的很分明了,这里剪短的概述下,这个类就是操作 epoll 相干的构造体的,所以啦,外面也基本上都是 JNI 办法

EPollArrayWrapper() throws IOException {
    // creates the epoll file descriptor
    epfd = epollCreate();

    // the epoll_event array passed to epoll_wait
    int allocationSize = NUM_EPOLLEVENTS * SIZE_EPOLLEVENT;
    pollArray = new AllocatedNativeObject(allocationSize, true);
    pollArrayAddress = pollArray.address();

    // eventHigh needed when using file descriptors > 64k
    if (OPEN_MAX > MAX_UPDATE_ARRAY_SIZE)
        eventsHigh = new HashMap<>();}
JNIEXPORT jint JNICALL
Java_sun_nio_ch_EPollArrayWrapper_epollCreate(JNIEnv *env, jobject this)
{
    /*
     * epoll_create expects a size as a hint to the kernel about how to
     * dimension internal structures. We can't predict the size in advance.
     */
    // 创立 epoll 构造体
    int epfd = epoll_create(256);
    if (epfd < 0) {JNU_ThrowIOExceptionWithLastError(env, "epoll_create failed");
    }
    return epfd;
}

new AllocatedNativeObject(allocationSize, true);

上面pollArray = new AllocatedNativeObject(allocationSize, true);

pollArray 正文为:来自 epoll_wait 的后果的 epoll_event 数组,然而看源码吧,也算不上数组,就开拓了一个内存块。

protected NativeObject(int var1, boolean var2) {
    // 略
    if (!var2) {this.allocationAddress = unsafe.allocateMemory((long)var1);
        this.address = this.allocationAddress;
    } else {
          // 获取内存页数
        int var3 = pageSize();
          // 开拓内存空间,返回地址
        long var4 = unsafe.allocateMemory((long)(var1 + var3));
        this.allocationAddress = var4;
        this.address = var4 + (long)var3 - (var4 & (long)(var3 - 1));
    }

}

pollWrapper.initInterrupt(fd0, fd1)

fd0: 后面 pipe 申请的读取端的文件描述符

上一篇咱们介绍了 epoll_ctl() 函数,
这里咱们重温下。epollCtl (epfd, EPOLL_CTL_ADD, fd0, EPOLLIN);
epfd 增加 fd0fd0可读,over~~

void initInterrupt(int fd0, int fd1) {
    outgoingInterruptFD = fd1;
    incomingInterruptFD = fd0;
    epollCtl (epfd, EPOLL_CTL_ADD, fd0, EPOLLIN);
}
JNIEXPORT void JNICALL
Java_sun_nio_ch_EPollArrayWrapper_epollCtl(JNIEnv *env, jobject this, jint epfd,
                                           jint opcode, jint fd, jint events)
{
    struct epoll_event event;
    int res;

    event.events = events;
    event.data.fd = fd;

    RESTARTABLE(epoll_ctl(epfd, (int)opcode, (int)fd, &event), res);

    /*
     * A channel may be registered with several Selectors. When each Selector
     * is polled a EPOLL_CTL_DEL op will be inserted into its pending update
     * list to remove the file descriptor from epoll. The "last" Selector will
     * close the file descriptor which automatically unregisters it from each
     * epoll descriptor. To avoid costly synchronization between Selectors we
     * allow pending updates to be processed, ignoring errors. The errors are
     * harmless as the last update for the file descriptor is guaranteed to
     * be EPOLL_CTL_DEL.
     */
    if (res < 0 && errno != EBADF && errno != ENOENT && errno != EPERM) {JNU_ThrowIOExceptionWithLastError(env, "epoll_ctl failed");
    }
}

ServerSocketChannel.open()

上面就来到了 channel,外部调用为sun.nio.ch.ServerSocketChannelImpl#ServerSocketChannelImpl(java.nio.channels.spi.SelectorProvider)

ServerSocketChannelImpl(SelectorProvider var1) throws IOException {super(var1);
    this.fd = Net.serverSocket(true);
    this.fdVal = IOUtil.fdVal(this.fd);
    this.state = 0;
}

Net.serverSocket(true)

这里看个办法名就大略晓得这是创立 socket 套接字的中央,各种协定规定之类的就跳过了,感兴趣的能够钻研下。

static FileDescriptor serverSocket(boolean var0) {return IOUtil.newFD(socket0(isIPv6Available(), var0, true, fastLoopback));
}
JNIEXPORT int JNICALL
Java_sun_nio_ch_Net_socket0(JNIEnv *env, jclass cl, jboolean preferIPv6,
                            jboolean stream, jboolean reuse, jboolean ignored)
{
    int fd;
    int type = (stream ? SOCK_STREAM : SOCK_DGRAM);
#ifdef AF_INET6
    int domain = (ipv6_available() && preferIPv6) ? AF_INET6 : AF_INET;
#else
    int domain = AF_INET;
#endif
    // 创立套接字
    fd = socket(domain, type, 0);
    if (fd < 0) {return handleSocketError(env, errno);
    }

#ifdef AF_INET6
    /* Disable IPV6_V6ONLY to ensure dual-socket support */
    if (domain == AF_INET6) {
        int arg = 0;
        if (setsockopt(fd, IPPROTO_IPV6, IPV6_V6ONLY, (char*)&arg,
                       sizeof(int)) < 0) {
            JNU_ThrowByNameWithLastError(env,
                                         JNU_JAVANETPKG "SocketException",
                                         "Unable to set IPV6_V6ONLY");
            close(fd);
            return -1;
        }
    }
#endif

    if (reuse) {
        int arg = 1;
        if (setsockopt(fd, SOL_SOCKET, SO_REUSEADDR, (char*)&arg,
                       sizeof(arg)) < 0) {
            JNU_ThrowByNameWithLastError(env,
                                         JNU_JAVANETPKG "SocketException",
                                         "Unable to set SO_REUSEADDR");
            close(fd);
            return -1;
        }
    }

#if defined(__linux__)
    if (type == SOCK_DGRAM) {
        int arg = 0;
        int level = (domain == AF_INET6) ? IPPROTO_IPV6 : IPPROTO_IP;
        if ((setsockopt(fd, level, IP_MULTICAST_ALL, (char*)&arg, sizeof(arg)) < 0) &&
            (errno != ENOPROTOOPT)) {
            JNU_ThrowByNameWithLastError(env,
                                         JNU_JAVANETPKG "SocketException",
                                         "Unable to set IP_MULTICAST_ALL");
            close(fd);
            return -1;
        }
    }
#endif

#if defined(__linux__) && defined(AF_INET6)
    /* By default, Linux uses the route default */
    if (domain == AF_INET6 && type == SOCK_DGRAM) {
        int arg = 1;
        if (setsockopt(fd, IPPROTO_IPV6, IPV6_MULTICAST_HOPS, &arg,
                       sizeof(arg)) < 0) {
            JNU_ThrowByNameWithLastError(env,
                                         JNU_JAVANETPKG "SocketException",
                                         "Unable to set IPV6_MULTICAST_HOPS");
            close(fd);
            return -1;
        }
    }
#endif
    return fd;
}

这里 newFD,就是创立一个对应的 java 对象,setfdVal()就是把文件描述符地址,放入到 java 对象中

public static FileDescriptor newFD(int var0) {FileDescriptor var1 = new FileDescriptor();
    setfdVal(var1, var0);
    return var1;
}
JNIEXPORT void JNICALL
Java_sun_nio_ch_IOUtil_setfdVal(JNIEnv *env, jclass clazz, jobject fdo, jint val)
{(*env)->SetIntField(env, fdo, fd_fdID, val);
}

ssc.socket().bind()

无聊的省略了,最初会到sun.nio.ch.ServerSocketChannelImpl#bind

public ServerSocketChannel bind(SocketAddress var1, int var2) throws IOException {synchronized(this.lock) {if (!this.isOpen()) {throw new ClosedChannelException();
        } else if (this.isBound()) {throw new AlreadyBoundException();
        } else {
            // 端口
            InetSocketAddress var4 = var1 == null ? new InetSocketAddress(0) : Net.checkAddress(var1);
            SecurityManager var5 = System.getSecurityManager();
            if (var5 != null) {var5.checkListen(var4.getPort());
            }
            NetHooks.beforeTcpBind(this.fd, var4.getAddress(), var4.getPort());
            // 最终会调用 bind 和 listen
            Net.bind(this.fd, var4.getAddress(), var4.getPort());
            Net.listen(this.fd, var2 < 1 ? 50 : var2);
            synchronized(this.stateLock) {this.localAddress = Net.localAddress(this.fd);
            }

            return this;
        }
    }
}

bind()

能够看到,channel 外面封装的 fd(Socket 文件描述符),后续也是把这个绑定端口。

public static void bind(FileDescriptor var0, InetAddress var1, int var2) throws IOException {bind(UNSPEC, var0, var1, var2);
}
static void bind(ProtocolFamily var0, FileDescriptor var1, InetAddress var2, int var3) throws IOException {boolean var4 = isIPv6Available() && var0 != StandardProtocolFamily.INET;
    bind0(var1, var4, exclusiveBind, var2, var3);
}
JNIEXPORT void JNICALL
Java_sun_nio_ch_Net_bind0(JNIEnv *env, jclass clazz, jobject fdo, jboolean preferIPv6,
                          jboolean useExclBind, jobject iao, int port)
{
    SOCKADDR sa;
    int sa_len = SOCKADDR_LEN;
    int rv = 0;

    if (NET_InetAddressToSockaddr(env, iao, port, (struct sockaddr *)&sa, &sa_len, preferIPv6) != 0) {return;}
    //
    rv = NET_Bind(fdval(env, fdo), (struct sockaddr *)&sa, sa_len);
    if (rv != 0) {handleSocketError(env, errno);
    }
}



int
NET_Bind(int fd, struct sockaddr *him, int len)
{
    // 略

    rv = bind(fd, him, len);

    // 略

    return rv;
}

listen()

listen()就很直白了,就相当于间接调用本地办法。

static native void listen(FileDescriptor var0, int var1) throws IOException;
JNIEXPORT void JNICALL
Java_sun_nio_ch_Net_listen(JNIEnv *env, jclass cl, jobject fdo, jint backlog)
{if (listen(fdval(env, fdo), backlog) < 0)
        handleSocketError(env, errno);
}

ssc.configureBlocking(false)

将文件描述符设置为 NIO,简略形容下略过啦

configureBlocking(int fd, jboolean blocking)
{int flags = fcntl(fd, F_GETFL);
    int newflags = blocking ? (flags & ~O_NONBLOCK) : (flags | O_NONBLOCK);

    return (flags == newflags) ? 0 : fcntl(fd, F_SETFL, newflags);
}

ssc.register(selector, SelectionKey.OP_ACCEPT);

在此之前先梳理下,

  • selector:就相当于 epoll 构造体,增加了 pipe() 创立的读取端文件描述符
  • channel:封装了创立的socket, 记录了套接字文件描述符,并且绑定了本地端口,并且开始监听申请
public final SelectionKey register(Selector sel, int ops,
                                   Object att)
    throws ClosedChannelException
{synchronized (regLock) {
        // 略
        if (k == null) {
            // New registration
            synchronized (keyLock) {if (!isOpen())
                    throw new ClosedChannelException();
                    //att :null 这里先疏忽
                k = ((AbstractSelector)sel).register(this, ops, att);
                addKey(k);
            }
        }
        return k;
    }
}
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);
        var4.attach(var3);
        synchronized(this.publicKeys) {
            // 对应不同零碎的实现
            this.implRegister(var4);
        }

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

implRegister()

SelectionKey外部封装了 channel,后面曾经很显著的看到,channel 创立的 Socket(套接字) 和 epoll 构造体之间并没有显示关联,在这里,就是进行关联。上面是 Epoll 的实现

fdToKey是 selector 初始化的时候创立的类型为 Map<Integer,SelectionKeyImpl>,就是将文件描述符和SelectionKey 关联起来, 最终会增加到EpollArrayWrapper::eventsLow, 此时 events=0

protected void implRegister(SelectionKeyImpl ski) {if (closed)
        throw new ClosedSelectorException();
    SelChImpl ch = ski.channel;
    int fd = Integer.valueOf(ch.getFDVal());
    fdToKey.put(fd, ski);
    pollWrapper.add(fd);
    keys.add(ski);
}
//pollWrapper.add(fd); 最终会调用
private void setUpdateEvents(int fd, byte events, boolean force) {if (fd < MAX_UPDATE_ARRAY_SIZE) {if ((eventsLow[fd] != KILLED) || force) {eventsLow[fd] = events;
        }
    } else {Integer key = Integer.valueOf(fd);
        if (!isEventsHighKilled(key) || force) {eventsHigh.put(key, Byte.valueOf(events));
        }
    }
}

在随后的 var4.interestOps(var2);eventsLow数组中 event 从 0 改成 POLLIN,此时还没有调用epollCtl() 增加进 epoll 构造体

selector.select(3000)

间接从 sun.nio.ch.EPollSelectorImpl#doSelect 开始

protected int doSelect(long timeout) throws IOException {if (closed)
        throw new ClosedSelectorException();
    processDeregisterQueue();
    try {begin();
        pollWrapper.poll(timeout);
    } finally {end();
    }
    processDeregisterQueue();
    int numKeysUpdated = updateSelectedKeys();
    if (pollWrapper.interrupted()) {
        // Clear the wakeup pipe
        pollWrapper.putEventOps(pollWrapper.interruptedIndex(), 0);
        synchronized (interruptLock) {pollWrapper.clearInterrupted();
            IOUtil.drain(fd0);
            interruptTriggered = false;
        }
    }
    return numKeysUpdated;
}

poll()

这里就能够很容易的看进去在每次 poll() 的时候会先把未注册的 Socket 套接字,通过调用 epollCtl() 增加进 epoll 构造体中

int poll(long timeout) throws IOException {updateRegistrations();
    updated = epollWait(pollArrayAddress, NUM_EPOLLEVENTS, timeout, epfd);
    // 这一段我猜想是中断操作,因为就算设置了 true,sun.nio.ch.EPollSelectorImpl#doSelect 中也会批改成 false。如有 dalao 欢送通知我
    for (int i=0; i<updated; i++) {if (getDescriptor(i) == incomingInterruptFD) {
            interruptedIndex = i;
            interrupted = true;
            break;
        }
    }
    return updated;
}
private void updateRegistrations() {synchronized (updateLock) {
        int j = 0;
        while (j < updateCount) {int fd = updateDescriptors[j];
            short events = getUpdateEvents(fd);
            boolean isRegistered = registered.get(fd);
            int opcode = 0;

            if (events != KILLED) {if (isRegistered) {opcode = (events != 0) ? EPOLL_CTL_MOD : EPOLL_CTL_DEL;
                } else {opcode = (events != 0) ? EPOLL_CTL_ADD : 0;
                }
                if (opcode != 0) {
                    // 这里增加进构造体
                    epollCtl(epfd, opcode, fd, events);
                    if (opcode == EPOLL_CTL_ADD) {registered.set(fd);
                    } else if (opcode == EPOLL_CTL_DEL) {registered.clear(fd);
                    }
                }
            }
            j++;
        }
        updateCount = 0;
    }
}

epollWait也就是对应的调用底层办法了,pollArrayAddress后面开拓的内存块,这里也就晓得干什么用了,也就是对应着epoll_event 构造体指针

JNIEXPORT jint JNICALL
Java_sun_nio_ch_EPollArrayWrapper_epollWait(JNIEnv *env, jobject this,
                                            jlong address, jint numfds,
                                            jlong timeout, jint epfd)
{struct epoll_event *events = jlong_to_ptr(address);
    int res;

    if (timeout <= 0) {           /* Indefinite or no wait */
        RESTARTABLE(epoll_wait(epfd, events, numfds, timeout), res);
    } else {                      /* Bounded wait; bounded restarts */
        res = iepoll(epfd, events, numfds, timeout);
    }

    if (res < 0) {JNU_ThrowIOExceptionWithLastError(env, "epoll_wait failed");
    }
    return res;
}

static int
iepoll(int epfd, struct epoll_event *events, int numfds, jlong timeout)
{
    jlong start, now;
    int remaining = timeout;
    struct timeval t;
    int diff;

    gettimeofday(&t, NULL);
    start = t.tv_sec * 1000 + t.tv_usec / 1000;

    for (;;) {int res = epoll_wait(epfd, events, numfds, remaining);
        if (res < 0 && errno == EINTR) {if (remaining >= 0) {gettimeofday(&t, NULL);
                now = t.tv_sec * 1000 + t.tv_usec / 1000;
                diff = now - start;
                remaining -= diff;
                if (diff < 0 || remaining <= 0) {return 0;}
                start = now;
            }
        } else {return res;}
    }
}

// 这一段我猜想是中断操作,因为就算设置了 true,sun.nio.ch.EPollSelectorImpl#doSelect 中也会批改成 false, 临时存疑。如有 dalao 欢送通知我

//sun.nio.ch.EPollArrayWrapper#poll    
for (int i=0; i<updated; i++) {if (getDescriptor(i) == incomingInterruptFD) {
        interruptedIndex = i;
        interrupted = true;
        break;
    }
}
    
//sun.nio.ch.EPollSelectorImpl#doSelect
if (pollWrapper.interrupted()) {
    // Clear the wakeup pipe
    pollWrapper.putEventOps(pollWrapper.interruptedIndex(), 0);
    synchronized (interruptLock) {pollWrapper.clearInterrupted();
        IOUtil.drain(fd0);
        interruptTriggered = false;
    }
}

updateSelectedKeys()

private int updateSelectedKeys() {
    int entries = pollWrapper.updated;
    int numKeysUpdated = 0;
    for (int i=0; i<entries; i++) {
        // 从 pollArrayAddress 找到 epoll_event 构造体
        int nextFD = pollWrapper.getDescriptor(i);
        // 找到对应的 SelectionKey
        SelectionKeyImpl ski = fdToKey.get(Integer.valueOf(nextFD));
        // ski is null in the case of an interrupt
        if (ski != null) {int rOps = pollWrapper.getEventOps(i);
            // 第一次没有
            if (selectedKeys.contains(ski)) {if (ski.channel.translateAndSetReadyOps(rOps, ski)) {numKeysUpdated++;}
            } else {ski.channel.translateAndSetReadyOps(rOps, ski);
                if ((ski.nioReadyOps() & ski.nioInterestOps()) != 0) {
                    // 增加进 selectedKeys 汇合
                    selectedKeys.add(ski);
                    numKeysUpdated++;
                }
            }
        }
    }
    return numKeysUpdated;
}

其余

到这里,整体脉络就很分明了剩下的这些也没必要剖析了,根本和上一篇外面的对应了,各位读者姥爷这么聪慧,就不节约大家工夫了

if(key.isReadable()){handleRead(key);
}
if(key.isWritable() && key.isValid()){handleWrite(key);
}
if(key.isConnectable()){System.out.println("isConnectable = true");
}

// 上面是 c
// 如果是新的连贯, 须要把新的 socket 增加到 efd 中
            if (ep[i].data.fd == listenfd )
            {connfd = accept(listenfd,(struct sockaddr*)&cliaddr,&clilen);
                tep.events = EPOLLIN;
                tep.data.fd = connfd;
                ret = epoll_ctl(efd,EPOLL_CTL_ADD,connfd,&tep);
            }
            // 否则, 读取数据
            else
            {connfd = ep[i].data.fd;
                int bytes = read(connfd,buf,MAXLEN);
                // 客户端敞开连贯
                if (bytes == 0){ret =epoll_ctl(efd,EPOLL_CTL_DEL,connfd,NULL);
                    close(connfd);
                    printf("client[%d] closed\n", i);
                }
                else
                {for (int j = 0; j < bytes; ++j)
                    {buf[j] = toupper(buf[j]);
                    }
                    // 向客户端发送数据
                    write(connfd,buf,bytes);
                }
            }

总结

  • Channel:对 socket 的封装
  • Selector:对 Epoll&epoll_event2 个构造体的封装
  • SelectionKey:关联下面 2 个,有了文件描述符疾速找到对应 Socket

参考文章

epoll:https://zh.wikipedia.org/wiki…

linux 文档:https://man7.org/linux/man-pa…

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