如何从 rust 中的多个线程传播错误？

Question

In a Rust application that is:

• Synchronous in the sense of not using "async"
• multi-threaded using std::thread
• threads are communicating via channels
• the "anyhow" crate is being used to annotate and propagate Results

I am propagating all errors up to the main thread, but I only see the Error that is hit by the main thread. This usually happens before I join the child threads, so I don't see the actual root cause.

What minimum-boilerplate modification can I make to see the Errors from multiple threads?

(I'll put some ideas I have in answers, but I'm hoping there is something better.)

Answer 1

I could use my main thread only for supervising child threads, aggregate all of their Results in some kind of Vec as I join them, filter it, and write custom code to print it.

This still feels like more work than should be necessary; I'm not the first person to write a threaded rust application that handles errors.

Answer 2

I could let threads panic and "propagate the panics":

https://doc.rust-lang.org/beta/std/thread/type.Result.html

But this is ugly:

• It introduces a difference between how errors are handled in child threads vs. the main thread.
• At every fallible call site in my original code I have to add.unwrap().
• If I unwrap() every error in the child threads, I might as well not even be using Result error handling, because everything will be returning Ok() or panicking. If I make that transformation, then I change the signature of all my existing functions, which is also gross.

Answer 3

One option would be to upgrade the entire application to use a logging framework, and then scrape through the logs.

This will require modifications everywhere have added an anyhow.context(), ensure,, or bail. annotation, to conditionally also throw a logger error.

Eventually I will want both logging/telemetry and clean teardown from propagating Results, but even then I will not want to have several lines of boilerplate for every single fallible function call.