Signals

Signals: Ctrl-C, a request to terminate and a hangup, received as values on a Channel so a program can shut down cleanly.

signals() returns a channel that receives each signal it names. No program code runs inside an operating-system signal handler: on POSIX the handler only writes a byte to a pipe, and a runtime thread turns that byte into a channel message; on Windows the console control handler already runs on a thread of its own and sends the message itself.

Source: runtime/process/signals.pep

Signal

enum Signal

A signal a program can receive from signals().

Cases

Interrupt

Interrupt

Ctrl-C: POSIX SIGINT, or Windows CTRL_C_EVENT and CTRL_BREAK_EVENT.

Terminate

Terminate

A request to end: POSIX SIGTERM, or Windows CTRL_CLOSE_EVENT, CTRL_LOGOFF_EVENT and CTRL_SHUTDOWN_EVENT.

Hangup

Hangup

The terminal closed: POSIX SIGHUP. Windows never sends it.

signals

signals(wanted: Array<Signal>): async.Channel<Signal>

Returns a new channel that receives each of wanted when the process gets it, instead of the signal’s default action (ending the program).

Receive from it like any channel: receive() waits outside a task and suspends inside one, and a task can select on it. Every channel that names a signal receives it. Closing the channel stops it receiving (the runtime lets go of it at the next signal or signals() call); once no open channel names a signal, the signal’s default action returns.

Nothing runs inside an operating-system signal handler, so the program reacts to a signal only by receiving from the channel. On Windows, the system ends the program a few seconds after Terminate (the console closing, a log-off or a shutdown) whatever it does, so clean up quickly. WASI has no signals: the channel never receives.

Parameters

• wanted — the signals the channel receives

Returns

• the channel

Example

import process;
import [Signal] from process;

main(): int {
    var stop = process.signals([Signal.Interrupt, Signal.Terminate]);
    start_serving();
    stop.receive();
    print("shutting down");
    stop_serving();
    return 0;
}