Signal default actions never restored after sig.dispose() called

[kevinkassimo]

Example:

const sig = Deno.signal(Deno.Signal.SIGINT);
// don't exit
const exitBlocker = setTimeout(() => {}, 100000);
await sig;
sig.dispose()
console.log("Signal disposed");
// Now if you try Ctrl-C it will still never exit the program, as default is never restored.

This is due to upstream Tokio behavior: See https://github.com/tokio-rs/tokio/blob/138eef352671aadffca304d62c69cb2582e64f2a/tokio/src/signal/unix.rs#L346-L361

It is debatable if we should reset to SIG_DFL ourselves, but it will break Tokio's handling due to Tokio having no idea we secretly resets and it relies on the presence of some SigInfo struct to determine if we have ever registered for listeners, meaning future reregistration will no longer work.

While it is probably more of a Tokio issue here if we want the default handling back, it might be worthy for us to discuss even if reset to default is the right thing to do. Also we need tracking of this issue on our side.

Notice Node.js does seem to reset to default correctly:

let counter = 0;
function handler() {
  console.log("Register");
  counter++;
  if (counter == 3) {
    console.log("Unregister");
    process.off('SIGINT', handler);
    // Ctrl-C after this kills the program
  }
}

process.on('SIGINT', handler);
setTimeout(() => {}, 100000);

[stale]

This issue has been automatically marked as stale because it has not had recent activity. It will be closed if no further activity occurs. Thank you for your contributions.

[lucacasonato]

@kevinkassimo Should I classify this is a bug? Is there something actionable to do here?

[stale]

This issue has been automatically marked as stale because it has not had recent activity. It will be closed in 7 days if no further activity occurs. Thank you for your contributions.

[bartlomieju]

Tokio documentation (https://docs.rs/tokio/1.5.0/tokio/signal/unix/struct.Signal.html#caveats) explicitly states that dropping a signal handler won't restore default behavior; we need to handle that situation ourselves. Most likely we'll need to keep track of number of registered/unregistered SIGINT signal and if it goes to zero we should add default handler that exits the process.

[Cre3per]

Tokio uses the signal_hook crate. signal_hook has an emulate_default_handler() function that can handle more signals than a custom SIGINT handler could. It also preserves exit codes by unregistering the handler and then re-raising the signal.