Question

我正在使用ioctlsocket（）函数使我的套接字无阻塞但是当我调用recvfrom（）时，我得到错误10035（WSAEWOULDBLOCK）。

u_long mode = 1;
ioctlsocket(newSocketIdentifier, FIONBIO, &mode);

while(1)
   {
      if((recv_len = recvfrom(newSocketIdentifier, receiveBuffer, sizeof(receiveBuffer), 0, (struct sockaddr *) &clientSocket, &clientSocketLength)) == SOCKET_ERROR)
      {
         char err[128];
         itoa(WSAGetLastError(),err,10);
         MessageBox( NULL,"Could not Receive Data",err,MB_ICONINFORMATION);
         BREAK;
      }
   }

有人可以解释为什么会这样吗？：（

Answer 1

如果没有可用的数据，这是正常的。代码是WSAEWOULDBLOCK（参见此表），意思是，在阻塞端口上，该函数必须等待，直到它可以被提供。

   while(1)
   {
      if((recv_len = recvfrom(newSocketIdentifier, receiveBuffer, sizeof(receiveBuffer), 0, (struct sockaddr *) &clientSocket, &clientSocketLength)) == SOCKET_ERROR)
      { 
         int ierr= WSAGetLastError();
         if (ierr==WSAEWOULDBLOCK) {  // currently no data available
             Sleep(50);  // wait and try again
             continue; 
         }

         // Other errors
         char err[128];
         itoa(ierr,err,10);
         MessageBox( NULL,"Could not Receive Data",err,MB_ICONINFORMATION);
         break;
      }
   }

Answer 2

我不同意这是上面所述的“正常”情况。

在您致电recvfrom时，您会收到recv_len的错误消息。我建议检查该值-它将是SOCKET_ERROR，并通过调用WSAGetLastErrorenter会看到错误WSAEWOULDBLOCK。

我不是（Windows）套接字专家，但是根据我的测试，我不能使用ioctlsocket和recvfrom的组合以非阻塞模式通过UDP接收数据（我做了同样的事情在您的示例中像您这样的事情。

我计划使用select和recvfrom的组合，并尽可能减少超时时间（1us）。我现在不知道任何其他可能更好的解决方案。

注意：您还应该检查ioctlsocket的返回值以了解可能的错误。

我将在今天晚些时候提供我的代码示例。

更新（按承诺添加代码）：

/* define list of sockets for function select(..) */
fd_set readfds;
/* define timeout for function select(..) */
TIMEVAL tv;
/* timeout: 1us */
tv.tv_usec = 1;
/* timeout: 0s */
tv.tv_sec = 0;
/* just 1 socket is used */
readfds.fd_count = 1;
readfds.fd_array[0] = receivingSocket;
/* determine the status of one or more sockets with timeout */
int selectReturnValue = select(0, &readfds, 0, 0, &tv);
/* check return value of the call of function select(..) */
switch (selectReturnValue)
{
  /* select(..) function timeout */
  case 0:
    /* time limit expired */
    break;
  /* select(..) function error */
  case SOCKET_ERROR:
    /* check the error status for the last windows sockets operation */
    selectError(WSAGetLastError());
    break;
  /* no timeout and no error */
  default:
    /* receive data from UDP */
    resultOfrecvfrom = recvfrom(receivingSocket, receivingBuffer, sizeof(receivingBuffer), 0, (SOCKADDR *)&serverReceptionInfo, &serverReceptionInfoLength);
    /* check result of call of recvfrom(..) */
    switch (resultOfrecvfrom)
    {
      /* connection has been gracefully closed  */
      case 0:
        /* socket was closed */
        break;
      /* socket error occurred during last call of socket operation */
      case SOCKET_ERROR:
        /* check the error status for the last Windows Sockets operation */
        recvfromError(WSAGetLastError());
        break;
      /* resultOfrecvfrom amount of data received */
      default:            
        /* ... add your code here */
        break;
    }
    break;      
}

如果需要更多内容，我只是复制了代码的关键部分，请在注释中告诉我。

recvfrom（）错误10035使用非阻塞套接字

2 个答案: