[Golang] 剑走偏锋 -- IoComplete ports

前言

Golang 目前的主要應用領域還是後臺微服務，雖然在業務領域也有所應用但仍然是比較小衆的選擇。大多數的服務運行環境都是linux，而在windows中golang應用更少，而作者因爲特殊情況，不得已要在widows環境中用golang去寫本地代理服務。在我的使用場景中實時性要求非常高（視頻通信），對tcp數據處理要足夠快，否則會造成TCP 服務端的 Receive Buffer 溢出造成 Packet loss，影響實時性和數據的完整性。

作者閲讀了golang 在windows 環境下 tcp 部分syscall 的實現，最終確認它的底層模型是用了完成端口（異步IO模型）的。
但是由於作者本人比較喜歡折騰，所以用golang 底層的syscall 實現了一下tcp 完成端口服務。

IoCompletion Port

以下為windows環境下用golang實現的 IoCompletion Port Server

IoCompletionRootContext

管理指定 Port 上所有 accepted socket:

type IoCompletionRootContext struct {
    socket     windows.Handle
    socketAddr windows.SockaddrInet4
    ioSet      []*IoCompletionContext

    sync.Mutex
}


func (root *IoCompletionRootContext) NewIoContext() *IoCompletionContext {
    root.Lock()
    defer root.Unlock()
    res := &IoCompletionContext{
        data: make([]byte, 65535),
        overlapped: windows.Overlapped{
            Internal:     0,
            InternalHigh: 0,
            Offset:       0,
            OffsetHigh:   0,
            HEvent:       0,
        },
    }

    res.wsaBuf.Buf = &res.data[0]
    res.wsaBuf.Len = uint32(65535)

    root.ioSet = append(root.ioSet, res)
    return res
}

func NewRootContext() *IoCompletionRootContext {
    return &IoCompletionRootContext{
        ioSet: make([]*IoCompletionContext, 0),
    }
}

IoCompletionContext

accepted socket 的上下文：

    type IoCompletionContext struct {
        socket     windows.Handle
        socketAddr windows.SockaddrInet4
        wsaBuf     windows.WSABuf
        data       []byte
        opType     OP_TYPE
        overlapped windows.Overlapped
    }

IoCompletionServer

完成端口服務:

type IoCompletionServer struct {
    Addr     string
    Port     int
    recvFunc func(data []byte) error
    rootCtx  *IoCompletionRootContext
    // 爲了防止内存移動，采用此種方式
    accepts           sync.Map
    hIOCompletionPort windows.Handle
}


func (ss *IoCompletionServer) saveIoRootCtx(id uint32, ctx *IoCompletionRootContext) {
    ss.accepts.Store(id, ctx)
}

func (ss *IoCompletionServer) loadIoRootCtx(id uint32) *IoCompletionRootContext {
    if id == uint32(ss.rootCtx.socket) {
        return ss.rootCtx
    }

    if v, isOk := ss.accepts.Load(id); isOk {
        if res, isOk := v.(*IoCompletionRootContext); isOk {
            return res
        }
    }

    return nil
}

func (ss *IoCompletionServer) remove(id uint32) {
    ss.accepts.Delete(id)
}

func (ss *IoCompletionServer) RegisterReceiveFunc(rfunc func([]byte) error) {
    ss.recvFunc = rfunc
}

func (ss *IoCompletionServer) Listen() {
    dwBytesTransfered := uint32(0)
    var ctxId uint32
    var overlapped *windows.Overlapped
    for {
        err := windows.GetQueuedCompletionStatus(ss.hIOCompletionPort, &dwBytesTransfered,
            &ctxId, &overlapped, windows.INFINITE)
        if err != nil {
            fmt.Printf("syscall.GetQueuedCompletionStatus: %v
", err)
        }

        if overlapped == nil {
            continue
        }

        // 通过位移取得ioCtx
        ioCtx := (*IoCompletionContext)(unsafe.Pointer(uintptr(unsafe.Pointer(overlapped)) - unsafe.Offsetof(IoCompletionContext{}.overlapped)))
        switch ioCtx.opType {
        case ACCEPT_POSTED:
            {
                ss.DoAcceptEx(ss.loadIoRootCtx(ctxId), ioCtx)
            }
        case RECV_POSTED:
            {
                ss.DoReceive(ss.loadIoRootCtx(ctxId), ioCtx)
            }
        case SEND_POSTED:
        case NULL_POSTED:
        default:
        }
    }
}

func (ss *IoCompletionServer) DoAcceptEx(rootCtx *IoCompletionRootContext, ioCtx *IoCompletionContext) (err error) {
    nFdCtx := NewRootContext()
    nFdCtx.socket = ioCtx.socket
    addrSize := uint32(unsafe.Sizeof(windows.RawSockaddrAny{}))

    var localAddr, remoteAddr *windows.RawSockaddrAny
    lrsalen := int32(addrSize)
    rrsalen := int32(addrSize)

    // 與windows C++ 不同，此處函數無需去函數指針即可使用
    windows.GetAcceptExSockaddrs(ioCtx.wsaBuf.Buf, ioCtx.wsaBuf.Len-(addrSize+16)*2,
        addrSize+16, addrSize+16, &localAddr, &lrsalen, &remoteAddr, &rrsalen)

    if ss.recvFunc != nil {
        ss.recvFunc(ioCtx.data[:ioCtx.overlapped.InternalHigh])
    }

    // 继承listen socket的属性
    err = windows.Setsockopt(nFdCtx.socket, windows.SOL_SOCKET, windows.SO_UPDATE_ACCEPT_CONTEXT,
        (*byte)(unsafe.Pointer(&ss.rootCtx.socket)), int32(unsafe.Sizeof(ss.rootCtx.socket)))
    if err != nil {
        return errors.Wrap(err, "syscall.AcceptEx")
    }

    err = windows.SetsockoptInt(nFdCtx.socket, windows.SOL_SOCKET, windows.SO_RCVBUF, 65535)
    if err != nil {
        return errors.Wrap(err, "windows.SetsockoptInt")
    }

    // 綁定到完成端口, 此步驟很關鍵
    handle, err := windows.CreateIoCompletionPort(nFdCtx.socket,
        ss.hIOCompletionPort, uint32(nFdCtx.socket), 0)
    if err != nil {
        return errors.Wrap(err, "syscall.CreateIoCompletionPort")
    } else {
        fmt.Println(handle, rootCtx.socket)
    }

    // 投遞接收請求, 此處可以自行修改
    for i := 0; i < 16; i++ {
        nFdIoCtx := nFdCtx.NewIoContext()
        nFdIoCtx.socket = nFdCtx.socket
        if err = ss.Receive(nFdIoCtx); err != nil {
            return err
        }
    }

    //投遞接收連接請求
    if err = ss.AcceptEx(ioCtx); err != nil {
        return err
    }

    // 保存到context中
    ss.saveIoRootCtx(uint32(nFdCtx.socket), nFdCtx)
    return nil
}

func (ss *IoCompletionServer) AcceptEx(ctx *IoCompletionContext) (err error) {
    ctx.socket = windows.Handle(C.mWSASocket())

    dwBytes := uint32(0)
    addrSize := uint32(unsafe.Sizeof(windows.RawSockaddrAny{}))
    ctx.opType = ACCEPT_POSTED
    //err = syscall.AcceptEx(ss.rootCtx.socket, ctx.socket, ctx.wsaBuf.Buf,
    //	ctx.wsaBuf.Len-2*(addrSize+16), addrSize+16,
    //	addrSize+16, &dwBytes, &ctx.overlapped)

    //windows.WSAIoctl(ss.rootCtx.socket, windows.SIO_GET_EXTENSION_FUNCTION_POINTER)
    err = windows.AcceptEx(ss.rootCtx.socket, ctx.socket, ctx.wsaBuf.Buf,
        ctx.wsaBuf.Len-2*(addrSize+16), addrSize+16,
        addrSize+16, &dwBytes, &ctx.overlapped)
    if err != nil {
        if err == windows.Errno(997) { // ERROR_IO_PENDING 表示尚未接收到鏈接
            err = nil
        } else {
            err = errors.Wrap(err, "syscall.AcceptEx")
        }
    }

    return err
}

func (ss *IoCompletionServer) DoReceive(rootCtx *IoCompletionRootContext, ctx *IoCompletionContext) {
    if ctx.overlapped.InternalHigh == 0 {
        if rootCtx != nil {
            ss.remove(uint32(rootCtx.socket))
            C.mClose(C.int(rootCtx.socket))
        }
        return
    }

    if ss.recvFunc != nil {
        ss.recvFunc(ctx.data[:ctx.overlapped.InternalHigh])
    }

    ss.Receive(ctx)
}

func (ss *IoCompletionServer) Receive(ioCtx *IoCompletionContext) error {
    recv := uint32(0)
    flags := uint32(0)
    ioCtx.opType = RECV_POSTED

    err := windows.WSARecv(ioCtx.socket, &ioCtx.wsaBuf,
        1, &recv, &flags, &ioCtx.overlapped, nil)
    if err != nil {
        if err == windows.Errno(997) { // ERROR_IO_PENDING 表示尚未接收到數據
            err = nil
        } else {
            err = errors.Wrap(err, "syscall.AcceptEx")
        }
    }

    return err
}

func setDefaultSockOpt(handle windows.Handle) error {
    err := windows.SetsockoptInt(handle, windows.SOL_SOCKET, windows.SO_REUSEADDR, 1)
    if err != nil {
        return errors.Wrap(err, "syscall.SetsockoptInt")
    }

    //err = windows.SetsockoptInt(handle, windows.SOL_SOCKET, windows.SO, 1)
    //if err != nil {
    //	return errors.Wrap(err, "syscall.SetsockoptInt")
    //}

    return nil
}

func (ss *IoCompletionServer) Start() error {
    fmt.Println(windows.WSAStartup(2, &windows.WSAData{}))

    // 初始創建一個用於綁定的 listen socket 的 IoCompletion 句柄
    hIOCompletionPort, err := windows.CreateIoCompletionPort(windows.InvalidHandle, 0, 0, 0)
    if err != nil {
        return errors.Wrap(err, "syscall.CreateIoCompletionPort")
    }

    ss.hIOCompletionPort = hIOCompletionPort

    rootCtx := NewRootContext()
    rootCtx.socket = windows.Handle(C.mWSASocket())
    setDefaultSockOpt(rootCtx.socket)
    ss.rootCtx = rootCtx

    handle, err := windows.CreateIoCompletionPort(rootCtx.socket,
        hIOCompletionPort, uint32(ss.rootCtx.socket), 0)
    if err != nil {
        return errors.Wrap(err, "syscall.CreateIoCompletionPort")
    } else {
        fmt.Println(handle, rootCtx.socket)
    }

    sockAddr := windows.SockaddrInet4{}
    sockAddr.Port = ss.Port

    if err := windows.Bind(rootCtx.socket, &sockAddr); err != nil {
        return errors.Wrap(err, "syscall.Bind")
    }

    if err := windows.Listen(rootCtx.socket, MAX_POST_ACCEPT); err != nil {
        return errors.Wrap(err, "windows.Listen")
    }

    ss.rootCtx = rootCtx

    if err := ss.AcceptEx(rootCtx.NewIoContext()); err != nil {
        return err
    }
    return nil
}

example

完成端口服務使用示例:

ss = &StreamServer{
    Addr: "127.0.0.1:10050",
    Port: 10050,
    accepts: sync.Map{},
}

ss.RegisterReceiveFunc(func(data []byte) error {
    fmt.Println("receive data len:", string(data))
    return nil
})

// 可以啓動多個携程來接收請求，但是需要特別注意的是
// 多携程可能會導致接受數據包時序發生亂序
ss.Listen()

結尾

以上代碼經過實際測試檢驗，可以正常使用，尚未與標準庫進行 效率性能 對比，沒有實現 send 功能,此處需要提醒的是,使用 IoCompletion Port 發送數據要注意時序的把握。

IoCompletion Port 是windows 系統中十分優秀的IO模型, 深入瞭解其工作機制及原理, 也有助於我們對操作系統 IO 數據處理的機制有更清晰的認知。

參考

• C++ 完成端口實現
• OVERLAPPED
• I/O Completion Ports
• CreateIoCompletionPort
• AcceptEx
• GetAcceptExSockaddrs