sigusr2.go

package main

import (
	"fmt"
	"os"
	"os/exec"
	"os/signal"
	"syscall"
)

func main() {
	args := os.Args[1:]
	sigChan := make(chan os.Signal, 1)
	signal.Notify(sigChan)

	for {
		cmd := exec.Command(args[0], args[1:]...)
		cmd.Stdout = os.Stdout
		cmd.Stderr = os.Stderr
		cmd.Stdin = os.Stdin
		cmd.SysProcAttr = &syscall.SysProcAttr{Setpgid: true, Pgid: 0}

		if err := cmd.Start(); err != nil {
			fmt.Fprintln(os.Stderr, err)
			os.Exit(1)
		}

		waitCh := make(chan error, 1)

		go func() {
			waitCh <- cmd.Wait()
			close(waitCh)
		}()

	signalLoop:
		for {
			select {
			case sig := <-sigChan:
				switch sig {
				case syscall.SIGUSR2:
					fmt.Fprintln(os.Stderr, "Caught SIGUSR2, restarting ...")
					if err := cmd.Process.Signal(syscall.SIGTERM); err != nil {
						fmt.Fprintln(os.Stderr, "SIGTERM to child failed ...")
					}
					status := <-waitCh
					if exitError, ok := status.(*exec.ExitError); ok {
						_ = exitError.Sys().(syscall.WaitStatus)
					}
					break signalLoop
				default:
					if err := cmd.Process.Signal(sig); err != nil {
						fmt.Fprintln(os.Stderr, "Signal to child failed ...")
					}
				}
			case err := <-waitCh:
				var waitStatus syscall.WaitStatus
				if exitError, ok := err.(*exec.ExitError); ok {
					waitStatus = exitError.Sys().(syscall.WaitStatus)
					os.Exit(waitStatus.ExitStatus())
				}
				if err != nil {
					fmt.Fprintln(os.Stderr, "Non-ok exit, oops")
				}
				return
			}
		}
	}
}