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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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[-] HaraldvonBlauzahn@feddit.org 1 points 10 hours ago

For Rust, return Result<> , as is idomatic in Rust.

Another possible method is having an installable handler that handles the error at the place it is detected. Common Lisp does that and it is very powerful.

[-] hades@programming.dev 2 points 4 hours ago
[-] eager_eagle@lemmy.world 7 points 16 hours ago* (last edited 16 hours ago)

you should do what's idiomatic for that language, e.g.: return an error in Rust; raise an exception in Python or Java; return an integer != 0 in C; etc.

Panic/crash/segfault

probably the worst option for a library

[-] senkora@lemmy.zip 3 points 15 hours ago

+1. If your library makes it impossible to recover from errors, then it will be unusable from any program that requires recovering from errors.

[-] hades@programming.dev 2 points 15 hours ago

probably the worst option for a library

Even worse than returning garbage? :)

[-] eager_eagle@lemmy.world 1 points 13 hours ago* (last edited 13 hours ago)

If it's garbage as in a string with a bunch of information that is hard to parse, yeah, crashing without giving the caller a way to avoid it might be worse. But what is exactly this garbage and in what cases are you considering returning it at all?

[-] hades@programming.dev 1 points 4 hours ago

Uninitialized automatic variables. E.g. (in C/C++):

int get_time() {
  int time;
  syscall(/* something that fails */, &time);
  return time;
}
[-] Colloidal@programming.dev 6 points 17 hours 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 17 hours 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 2 points 11 hours 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 8 hours 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.

[-] Treczoks@lemmy.world 3 points 16 hours ago

Return an error, respectively, in a language that supports it, raise an exception.

In my systems, nearly every call returns a status, and it is advisable to check this status. I had a number of long calls with windows programmers who complained about my system failing at some point, and most often, the reason was an ignored Non-OK status return at some point in the past.

Like "Your system loses the file I'm writing!". FileSystem_Open() returned a non-OK value (I don't remember the reason, but there was one). FileSystem_Write() returned a non-OK value (file pointer invalid). FileSystem_Close() returned a non-OK value (file pointer invalid). And he complains about a file that is not there...

[-] anton 2 points 17 hours ago

I think you should make the overwhelmingly likely case crash in a controlled way, but provide a way to handle it for people who truly want to keep going in such strange conditions.

In rust I would panic in now(), but also provide a alternative call that returns a result named something like try_now(), similar to Vec::with_capacity and Vec::try_with_capacity.
In languages that provide them, you could also throw a runtime exception that can be ignored and just bubbles up to main unless explicitly caught.

[-] hades@programming.dev 4 points 15 hours ago

Interestingly, Rust is what brought me to this rabbit hole. It does indeed panic in now()[1], but the devs seem to be reluctant to provide the try_now() variant[2].

[1] https://doc.rust-lang.org/nightly/src/std/sys/pal/unix/time.rs.html#124 [2] https://github.com/rust-lang/rust/issues/115482

this post was submitted on 04 Aug 2025
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