Comment by dnautics
19 hours ago
stacktraces? might also be useful to know whether or not the latest allocand was a jumbo sized allocand that caused the failure?
19 hours ago
stacktraces? might also be useful to know whether or not the latest allocand was a jumbo sized allocand that caused the failure?
Do you really want that data passed back down to the caller of the allocation? From the description of the failure state you'd want to log that data instead: what's the caller of the allocation going to do if you tell it it failed with a crazy size? It already knows the size, it's the one who asked for it.
So, suppose it's a rust library -- you're locking me into whatever logging system the library author chooses? Maybe I'd like to consume the relevant data at the entry point and send it to a logging system of my choice.
A Rust library likely wouldn't be returning an opaque Box<dyn Error> to begin with. Errors are part of a library's API—it's what allows consumers to handle them—so you'd define an enum of possible errors your library could produce and return that, which would be stored on the stack.
5 replies →
it depends, if the functionality represented by the library is known to require a lot of memory (or simply allocation failures are an expected part of its operation), then it should be pretty much part of the API, probably with some tracing/diagnostics interface to get the required visibility into how much memory goes and where.
but for most libraries I on allocation failure I don't expect any fancy logging system. maybe even panic is fine.
usually “stdout” is good enough, wrapper/runner routes output to logserver for collation and search. who cares about formats as long as it’s reasonably structured and searchable?
And how do you store a stacktrace without allocating?
Any time I mention "but I would like stacktraces with my errors" I get told I'm doing it wrong.
That's because the types of errors where you want a stack trace are a relatively small subset of all possible errors.
Stack traces are only useful for errors that indicate a bug in the program, i.e. something a programmers has to respond to. It's not useful for the vast class of bugs that are a result of wrong input, wrong external state, or infrastructure issues.
Rust projects tend to favor panicking over error handling for programmer bugs (which does indeed give you a stack trace depending on environment variables), or even better encoding the invariants in the type system, but there are cases where an error coming from a library are truly, actually unexpected, so both `anyhow` and `thiserror` do provide support for attaching a stack trace in those situations.
See? You get people explaining to you that you actually don't want a stack trace because xyz.
If you let the allocation error panic you will get your stack trace.
You can't have a stack trace on an error in the error path that failed to allocate. If you have a "jumbo sized" error and the error fails to allocate, it won't get reported. The only reporting you will get is that the error failed to allocate and this new allocation error overrides the error that failed to allocate.