Socket SO_RCVTIMEO 超时是 C++/VC++ 中设置值的两倍

Question

Please, show below example

int val = 120000;
setsockopt(connSock,SOL_SOCKET,SO_RCVTIMEO,(char*)&val,sizeof(int));

I set 120 seconds at receive timeout but it takes 240 seconds.

I think timeout is double the set value.

how is it possible?

Answer 1

SO_RCVTIMEO and SO_SNDTIMEO do not work on all socket operations, you should use non-blocking mode and select .

The behaviour may change on different operating system configurations. On my system the connect timeouts after two times the value I set in SO_RCVTIMEO. A quick hack like setting SO_RCVTIMEO to x/2 before a connect and x after it works, but the proper solution is using select.

References

Discussion on this problem (read comments to answer):

• https://stackoverflow.com/a/4182564/4074995

How to use select to achive the desired result:

• http://beej.us/guide/bgnet/output/html/multipage/advanced.html#select
• C: socket connection timeout

Answer 2

SO_RCVTIMEO does not accept an int as the timeout. You're looking for something like this:

struct timeval tv = {
    .tv_sec = 120
};

setsockopt(connSock, SOL_SOCKET, SO_RCVTIMEO, &tv, sizeof(tv));