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Handling of unlikely syscall errors (programming.dev)
submitted 3 weeks ago by hades@programming.dev to c/programming@programming.dev
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If you were designing a standard library of a high level language (like Rust, C++, etc.) what would it do if while getting the current time of day (e.g. SystemTime::now()) it encountered a failed kernel system call (e.g. to clock_gettime) and why?

What do you think the existing implementations do?

  • Return error or raise exception
  • Return 0
  • Return undefined values (like stack garbage)
  • Panic/crash/segfault
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[-] Colloidal@programming.dev 6 points 3 weeks ago

Raising an exception would be standard practice, IMO. A library should not dictate how an application behaves. Let the application handle it.

[-] sxan@midwest.social 1 points 3 weeks ago

If that's the only error mechanism, sure. Exceptions in most languages tend to be relatively expensive, though, and most have a cheaper idiomatic way of returning error codes; you'd want to use those if they're available, right?

Does Rust use exceptions a lot? I don't know. V has panic and catch, but you almost never see them. Idiomatic is Option (?) and Return (!) values, which I thought V borrowed from Rust. Go does the (val, error) tuple-ish return thing, and while it too has catchable panics, they're discouraged in favor of (error) return values.

Depends on the language. "Higher level" is a pretty broad field!

[-] bleistift2@sopuli.xyz 3 points 3 weeks ago

If that’s the only error mechanism, sure. Exceptions in most languages tend to be relatively expensive, though, and most have a cheaper idiomatic way of returning error codes; you’d want to use those if they’re available, right?

I think not being able to get the current time from the system is very exceptional. And I think exceptional circumstances should act that way and not “look like” normal executions. To me, that means letting hell break loose, and not “silently” return a 1 instead of a 0.

By similar reasoning, “Exceptions in most languages tend to be relatively expensive” is a very weak argument. We don’t expect this error-throwing code to execute a lot.

[-] sxan@midwest.social 1 points 3 weeks ago

I can think if plenty of situations where system time is

  • Optional
  • Unreliable
  • And even potentially disallowed by the user

In fact, if you don't set up your containers right, the system time is almost always wrong.

this post was submitted on 04 Aug 2025
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