SO_RCVTIMEO ,  MSG_WAITALL

 test SO_RCVTIMEO and MSG_WAITALL 

1.首先两者都运用于阻塞的情景下，对nonblock的fd不起作用。

2.SO_RCVTIMEO, socket选项，作为getsockopt, setsockopt的参数。见下 figure1. 

SO_RCVTIMEO选项可以指定阻塞调用的超时时长，SO_RCVTIMEO的影响的函数read, readv, recv, recvfrom, recvmsg.

3.MSG_WAITALL, recv调用的参数，

 MSG_WAITALL
              On  SOCK_STREAM  sockets  this  requests that the function block
              until the full amount of data can be returned. The function  may
              return  the  smaller  amount of data if the socket is a message-
              based socket, if a signal is caught, if the connection is termi‐
              nated,  if MSG_PEEK was specified, or if an error is pending for
              the socket.



ps:
recv(sockfd, buff, buff_size, MSG_WAITALL),
在正常情况下recv 是会等待直到读取到buff_size 长度的数据，但是这里的WAITALL 也只是尽量读全，在有中断的情况下recv 还是可能会被打断&