堵塞模式的recv怎么会报Ewouldblock错误？
RT：
windows下是没有问题的
代码移植到linux下，就报了EWOULDBLOCK错误，此错误不是在非堵塞模式下 才会出现的吗？
[解决办法]
是设置了SO_RCVTIMEO 吧
[解决办法]
SO_RCVTIMEO
Sets the timeout value that specifies the maximum amount of time an input function waits until it completes. It accepts a timeval structure with the
number of seconds and microseconds specifying the limit on how long to wait for an input operation to complete. If a receive operation has blocked
for this much time without receiving additional data, it shall return with a partial count or errno set to [EAGAIN] or [EWOULDBLOCK] if no data is
received. The default for this option is zero, which indicates that a receive operation shall not time out. This option takes a timeval structure.
Note that not all implementations allow this option to be set.
