ACE_Stream中的recv_n和send_n

ACE_Stream中提供recv_n函數，該函數要求輸入參數len表示要接受的字節數。

當代碼中調用該函數時，程序會一直阻塞在recv_n函數調用的地方，只到recv_n對應的描敘符接收到了len個字節或者連接斷開。

recv_n代碼：

ACE::recv_n_i (ACE_HANDLE handle,
               void *buf,
               size_t len,
               int flags,
               size_t *bt)
{
  size_t temp;
  size_t &bytes_transferred = bt == 0 ? temp : *bt;
  ssize_t n;

  for (bytes_transferred = 0;
       bytes_transferred < len;
       bytes_transferred += n)
    {
      // Try to transfer as much of the remaining data as possible.
      n = ACE_OS::recv (handle,
                        static_cast <char *> (buf) + bytes_transferred,
                        len - bytes_transferred,
                        flags);
      // Check EOF.
      if (n == 0)
        return 0;

      // Check for other errors.
      if (n == -1)
        {
          // Check for possible blocking.
          if (errno == EWOULDBLOCK)
            {
              // Wait for the blocking to subside.
              int const result = ACE::handle_read_ready (handle, 0);

              // Did select() succeed?
              if (result != -1)
                {
                  // Blocking subsided.  Continue data transfer.
                  n = 0;
                  continue;
                }
            }

          // Other data transfer or select() failures.
          return -1;
        }
    }

  return static_cast<ssize_t> (bytes_transferred);
}