go grpc error: code = Unavailable desc = connection closed before server preface received

Question

when I start 1600 rpc clients to request an rpc server concurrently. Only about 100 Clinets can request successfully, and the rest report the following error： rpc error: code = Unavailable desc = connection closed before server preface received

this is my code

init the client

var (
    threads   = 1600
    reqlength = 122
    port      = 8011
)

func (this *RpcClient) init(addr string) bool {
    this._p_addr = &addr
    //maxSize := 300 * 1024 * 1024
    //diaOpt := grpc.WithDefaultCallOptions(grpc.MaxCallRecvMsgSize(maxSize), grpc.MaxCallSendMsgSize(maxSize))

    conn, err := grpc.Dial(*this._p_addr, grpc.WithInsecure())
    if err != nil {
        fmt.Printf("node server cli, dia server %s failed: %v", addr, err)
        return false
    }

    this._conn = conn
    this._client = pb.NewTestQPSClient(conn)
    if this._client == nil {
        fmt.Printf("node server cli init connect failed %s", addr)
        return false
    }

    return true

}

create 1600 clients and request the rpc server concurrently

func main() {
    fmt.Printf("start client with %d threads  size %d\n", threads, reqlength)
    //_cli := RpcClient{}
    //_cli.init("localhost:8010")
    wg := sync.WaitGroup{}
    for j := 0; j < threads; j++ {
        wg.Add(1)

        go func(x int) {
            defer wg.Done()
            _cli := RpcClient{}


            _cli.init(fmt.Sprintf("127.0.0.1:%d", port))

            buf := make([]byte, reqlength)
            //for {
            req := pb.Req{}

            //rand.Read(buf)
            req.ReqData = buf

            _, err := _cli._client.LoadData(context.Background(), &req)
            if err != nil {
                fmt.Println(err.Error())
                return
            }
            //}

        }(j)
    }
    wg.Wait()
}

I got the error:

rpc error: code = Unavailable desc = connection closed before server preface received
rpc error: code = Unavailable desc = connection closed before server preface received
......
rpc error: code = Unavailable desc = connection closed before server preface received
rpc error: code = Unavailable desc = connection closed before server preface received