Add signal handlers

[kt3k]

This PR adds signal handler APIs. Deno.signal(signo) function returns an async iterator of the given signal number. The returned object also works as a promise which is resolved when the first signal is received.

Streaming API

for await (const _ for Deno.signal(Deno.Signal.SIGTERM)) {
  console.log("SIGTERM received!");
}

Promise API

await Deno.signal(Deno.Signal.SIGTERM);
console.log("SIGTERM!");

The stream can be disposed by calling .dispose() method.

const sig = Deno.signal(Deno.Signal.SIGTERM);
setTimeout(() => { sig.dispose(); }, 5000);

for await (const _ of sig) {
  console.log("SIGTERM received!");
}

The above for-await-of loop exits after 5000ms.

Note: Signal handlers doesn't block the program exiting. The following program exits immediately.

await Deno.signal(Deno.Signal.SIGTERM);

Signal handlers must be used with some other main things, such as servers, etc, and those main routines should block the program from exiting. See the discussions in #3721 #3715 for details.

---

This PR also adds the following shorthand functions:

Deno.signals.alarm(); // for SIGALRM
Deno.signals.child(); // for SIGCHLD
Deno.signals.hungup(); // for SIGHUP
Deno.signals.info(); // for SIGINFO
Deno.signals.interrupt(); // for SIGINT
Deno.signals.io(); // for SIGIO
Deno.signals.pipe(); // for SIGPIPE
Deno.signals.quit(); // for SIGQUIT
Deno.signals.terminate(); // for SIGTERM
Deno.signals.userDefined1(); // for SIGUSR1
Deno.signals.userDefined2(); // for SIGURS2
Deno.signals.windowChange(); // for SIGWINCH

These shorthand names are inspired by methods of tokio::signal::unix::SignalKind.

---

Internals

This PR adds 3 ops:

• op_bind_signal (start watching signals) - Sync
• op_poll_singal (poll single signal) - AsyncUnref
• op_unbind_signal (stop watching signals) - Sync

And 1 resource:

• SignalStreamResource

---

closes #2339
ref #3610 (an older version of this PR)

[ry]

@kt3k Is this working now? It looks like it.

[kt3k]

@ry Yes, this is ready for review now. PTAL.

cc @bartlomieju @kevinkassimo

[bartlomieju]

Why is run permission needed here?

[kt3k]

Sorry. A mistake. Will remove.

[bartlomieju]

Seems superfluous... just return done?

[bartlomieju]

How about single SignalArgs?

[bartlomieju]

Maybe guard against additional calls to dispose()

[kt3k]

Sounds a good idea.

[ry]

Would be better to call these

OP_SIGNAL_BIND
OP_SIGNAL_UNBIND
OP_SIGNAL_POLL

[axetroy]

Is now able to listen to multiple signals at once?

If it can, it must be excellent

[kt3k]

@axetroy Sorry. I haven't included that feature in this PR because this one is already a little big (to me) and I'm not so sure about the interface of that feature (Deno.signal(Signal.SIGTERM, Signal.SIGINT) ? or some other function in deno_std?). I'd like to duscuss about the interface of that feature in another issue first. (I created #3773.)

[ry]

LGTM - very nice patch in the end ! Thank you for seeing this through @kt3k.