Comment by cbsmith | Hacker News Reader

Comment by cbsmith | Hacker News Reader

So, this slide confused/troubled me: http://www.openbsd.org/papers/eurobsdcon_2013_time_t/mgp0002...

I don't see why it would be a good idea to convert "time_t" to "long long". Having an alias specifically for time_t is part of what makes this kind of work doable. I could see maybe introducing another alias like "time64_t" or something, but once you convert it to "long long" the type is no longer tagged in a way that makes it easy to find and more importantly suggests to the programmer they ought to NOT make assumptions about its size. Heck, in a perfect world I'd either introduce a new % symbol specifically for time_t width or have a macro that expands to represent its width (not to mention make it mandatory to use compiler warnings about string formats not matching argument widths).

I also found the comment about "would love better compiler tools -- none found so far". Certainly there are things like Sparse (https://sparse.wiki.kernel.org/index.php/Main_Page) which correctness verification easier.

The typedef 'time_t' is definitely being used, for example is is a patch from sys/kern/kern_clock.c: http://www.openbsd.org/cgi-bin/cvsweb/src/sys/kern/kern_cloc...

That was part of a larger changeset that enabled 64bit time_t on 2013-08-13. The 'long' type is changed to 'time_t', which is now 64bit everywhere on OpenBSD.

I didn't see think talk but I think it's confusing because we are just seeing the slides. Here is what I got from it:

    remove time_t from network/on-disk/database formats

Right now if you have a userspace app that has some kind of binary disk format, say a database, and you use the time_t typedef your binary files will not be portable between systems which have differently sized time_t's. However, if you use 'long long' or 'int64_t' and cast time_t's to those, your files will be portable and 64bit everywhere.

If you're using time_t in network formats, systems with different time_t sizes will confuse each other!

    remove as many (time_t) casts as possible

This is trouble because you don't know the size of time_t, if it's 32bit you might be truncating! It's better to cast to a 64bit size, that will always work, at least for the next 292 billion years.

Thanks. This makes much more sense sense now. I'd still be tempted to use some kind of a typedef for the field, but yeah, you'd not want to derive it from the system's time_t structure.

Yes that's about right. The videos will be up at some point but it was a two phase process like that.

The slides are confusing to me too, another slide [1] states that they will change time_t to be "long long" in a future release so the tagged type will still be there.

I'm also not sure why the OpenBSD people think that there will be lots of problems with ports [2], I'm typing this on a NetBSD system with 64 bit time_t, things that broke have had patches pushed upstream.

[1] http://www.openbsd.org/papers/eurobsdcon_2013_time_t/mgp0003... [2] http://www.openbsd.org/papers/eurobsdcon_2013_time_t/mgp0003...

Introducing a new format specifier for every typedef will quickly exhaust the alphabet.

In 292 billion years when we overflow a 'long long' time_t humanity is really going to regret that flippant attitude.

I agree, and consider that one of the inherent problems with the string formatter approach to IO. That said, time is perhaps one of the data types that is universal enough and general enough to the C runtime that you could make a case for it.

I've always felt that the 'right' solution was to emulate glibc and provide facilities for registering new format specifiers[1]. Then libraries could provide specifiers for everything that made sense and users could pick and choose.

Of course, there would be performance implications - not to mention the added complexity for implementors.

[1]http://www.gnu.org/software/libc/manual/html_node/Customizin...

What happens when your graphics library and your network library pick the same letter?

The simplest solution (from the implementor's perspective) is probably to leave it to the user to reassign one. Allowing multiple-letter specifiers helps here. Coming from a C perspective, that's what I would prefer.

You could work out all sorts of namespacing and automatic reassignment schemes, of course.

I can't think of anything without trade-offs off the top of my head (I double that anything exists), but in my (limited) experience it's very workable.

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