Signals

valk.signal lets a program react to Ctrl+C, kill and the other process signals. Your code never runs inside the signal handler itself, so it may do anything a normal function does.

Stop cleanly on Ctrl+C#

cancel_on_shutdown cancels a sync.CancelToken when SIGINT or SIGTERM (and SIGHUP where it exists) arrives. Wait on the token, then shut down:

use valk.signal
use valk.sync
use valk.http

fn handle(req: http.Request) http.Response {
    return http.Response.text("Hello")
}

fn main() {
    let stop: sync.CancelToken = sync.CancelToken.new() ! return
    signal.cancel_on_shutdown(stop) ! return

    let server = http.Server.new("127.0.0.1", 8080, handle)
    let running = co server.start()
    stop.wait()
    println("Shutting down")
    server.shutdown()
    await running ! return
}

cancel_on(sig, token) does the same for one signal. An HTTP server can also do this by itself: see graceful shutdown.

The signals#

Functions throw unsupported for a signal the platform does not have.

Run code or wait for a signal#

use valk.signal

fn main() {
    signal.on(.user1, fn() { println("got SIGUSR1") }) ! return
    let waiting = co signal.wait(.user1, 2000)
    signal.raise(.user1) ! return
    let arrived = await waiting ! return
    println(arrived) // true
}

A callback from on runs on another thread, so it is an atomic fn: it may capture numbers and atomic values (see Threads).

Signal a child process#

A started process takes the same enum: child.signal(.terminate).