elvish/pkg/eval/interrupts.go

package eval

import (
	"context"
	"errors"
	"os"
	"os/signal"
	"syscall"
)

// Context returns a Context associated with the Frame.
func (fm *Frame) Context() context.Context {
	return fm.ctx
}

// CancelCause checks whether the Context of the Frame has been canceled, and if
// so, returns a non-nil error.
func (fm *Frame) CancelCause() error {
	select {
	case <-fm.ctx.Done():
		return context.Cause(fm.ctx)
	default:
		return nil
	}
}

// ErrInterrupted is thrown when the execution is interrupted by a signal.
var ErrInterrupted = errors.New("interrupted")

// Used to "cancel" a finished evaluation. It is a bug if this actually cancels
// anything.
var errEvalFinished = errors.New("internal bug, eval should have finished")

// ListenInterrupts returns a Context that is canceled when SIGINT or SIGQUIT
// has been received by the process. It also returns a function to cancel the
// Context, which should be called when it is no longer needed.
func ListenInterrupts() (context.Context, func()) {
	sigCh := make(chan os.Signal, 1)
	signal.Notify(sigCh, syscall.SIGINT, syscall.SIGQUIT)
	// Channel to return, closed after receiving the first SIGINT or SIGQUIT.
	ctx, cancel := context.WithCancelCause(context.Background())

	go func() {
		select {
		case <-sigCh:
			cancel(ErrInterrupted)
		case <-ctx.Done():
		}
		signal.Stop(sigCh)
	}()

	return ctx, func() {
		cancel(errEvalFinished)
	}
}