smol-rs / async-signal Goto Github PK

I'm looking into packaging this crate for Fedora Linux as a new dependency of the async-process crate. Currently this crate does not include any license texts, but both the MIT and the Apache-2.0 license require that (re)distributed sources contain a copy of the license text. This is a problem from a distribution point of view, and blocks work on providing a package for this crate (and updating async-process to the latest versions).

Linux supports signalfd, which can be used to wait for signals in epoll without needing to clone several pipes like we do in the current implementation. On Linux, we should use that instead.

Right now, when a signal is registered via the Signals type, the default signal handler is disabled. This requires the user to manually call the low-level signal handler. This is probably what's desired for most cases, like handling SIGINT, since the default signal handler for SIGINT ends the application. However, for other signals, it may be desired to call the default signal handler. I think there should be an option in add_signals or other to call the default signal handler on receipt.

kqueue supports EVFILT_SIGNAL, which would allow us to wait on a signal without needing to use a pipe. I'm working on exposing this functionality in async-io via smol-rs/async-io#112. However, this would require setting up an executor to listen for signals.

Windows supports signals as well (albeit a significantly smaller set than what Unix supports). It would be good to support those signals here.

However, the current notification (an asynchronous pipe) isn't supported by async-io yet. We could either use Windows UDS sockets, which would work out of the box in this case but aren't available on older versions of Windows, or we could work named pipes into async-io/polling, which would be harder but also open up more opportunities.

concurrent-queue is imported (in Cargo.toml) only if target is linux, but is used when target is linux OR android.

So, async-signal last release (v0.2.1) does not build on android target.

Thank you !

Cargo.toml

[target.'cfg(target_os = "linux")'.dependencies]
concurrent-queue = "2.2.0"

lib.rs

} else if #[cfg(any(target_os = "android", target_os = "linux"))] {
    mod signalfd;
    use signalfd as sys;
}

signalfd.rs

use concurrent_queue::ConcurrentQueue;