net: document Dial thread safety, timeout example #33743
Description
I'm trying to figure out whether port 80 on the IP address 169.254.169.254 is reachable from the host I'm on. Essentially all I want to do is connect to it with a short timeout. I'm a little confused by the net package on this point.
- Generally speaking I thought timeouts were deprecated in favor of using a context with a timeout parameter. However, the
netpackage still has aDialTimeouttop level function and noDialContext. - There is a
(*Dialer) DialContext()method. After some reading I see that the empty Dialer is equivalent to callingnet.Dial, there's no DefaultDialer or similar. However, is a Dialer safe to use concurrently? (eg. If I am going to use DialContext, can I just have one package-level Dialer or similar, instead of allocating a new one each time.) It's not clear from the documentation.
It might be good to have some examples here, some guidance about when to use Context vs. Timeout, and a short note about whether a Dialer is safe for concurrent use.