Help understanding why futures::io::copy returns WriteZero error in FRB

[tmpfs]

I have some code in a library dependency (which I maintain) that uses futures::io::copy to copy data from a reader to a writer.

When I test that code outside of FRB it works as expected however when I call it via FRB the futures::io::copy is returning a WriteZero (io::ErrorKind).

In my API functions I am using #[tokio::main(flavor = "current_thread")] as recommended.

I suspect it is something to do with the FRB threadpool but looking for some ideas as to where the problem might be.

Thanks 🙏

[tmpfs]

I think this is the error i am hitting:

https://docs.rs/futures-util/0.3.28/src/futures_util/io/copy_buf.rs.html#72

What i fail to understand is why this only happens when using FRB, ideas welcome!

[fzyzcjy]

Hmm, firstly, is it only happen with the threadpool crate we are using? If so it can be a bug there.

[tmpfs]

@fzyzcjy, I tried to reproduce the problem using #[tokio::main] inside a threadpool but unable to reproduce it yet, will keep trying to figure out why this is happening.

[fzyzcjy]

Hmm, what if you disable threadpool of frb (by maybe hacking it)?

[tmpfs]

@fzyzcjy, I tried also with worker-single just in case but that had no effect.

[tmpfs]

This is the code (extracted from the library) that is causing the issue when run via FRB https://github.com/tmpfs/threadpool-futures-io-copy but works fine with just cargo run.

Next I guess I need to move this into a standalone FRB project to try to reproduce.

[tmpfs]

FWIW, if anyone stumbles across this, the bug is no longer present when using FRB v2 🥳