func start()

in cmds/exec_agent/verbs.go [75:160]
68 lines of code
15 McCabe index (conditional complexity)

func start(bin string, args []string) error {
	ctx := xcontext.Background()

	// signal channel for process exit. Similar to Wait
	reaper := newSafeSignal()
	defer reaper.Signal()

	if flagTimeQuota != nil && *flagTimeQuota != 0 {
		var cancel xcontext.CancelFunc
		ctx, cancel = xcontext.WithTimeout(ctx, *flagTimeQuota)
		defer cancel()

		// skip waiting for remote to poll/wait
		go func() {
			<-ctx.Done()
			reaper.Signal()
		}()
	}

	cmd := exec.CommandContext(ctx, bin, args...)

	var stdout, stderr SafeBuffer
	cmd.Stdout = &stdout
	cmd.Stderr = &stderr

	log.Printf("starting command: %s", cmd.String())
	if err := cmd.Start(); err != nil {
		return fmt.Errorf("failed to start process: %w", err)
	}
	// NOTE: write this only pid on stdout
	fmt.Printf("%d\n", cmd.Process.Pid)

	cmdErr := make(chan error, 1)
	go func() {
		err := cmd.Wait()
		if err != nil {
			log.Printf("process exited with err: %v", err)
		} else {
			log.Print("process finished")
		}

		reaper.Wait()
		cmdErr <- err
	}()

	// start unix socket server
	mon := NewMonitorServer(cmd.Process, &stdout, &stderr, reaper)
	monErr := make(chan error, 1)
	go func() {
		monErr <- mon.Serve()
	}()

	// catch termination signals
	sigs := make(chan os.Signal, 1)
	defer close(sigs)
	signal.Notify(sigs, syscall.SIGINT, syscall.SIGTERM)

	for {
		select {
		case err := <-cmdErr:
			if err := mon.Shutdown(); err != nil {
				log.Printf("failed to shutdown monitor: %v", err)
			}
			return err

		case sig := <-sigs:
			if err := mon.Shutdown(); err != nil {
				log.Printf("failed to shutdown monitor: %v", err)
			}
			if cmd.ProcessState == nil {
				if err := cmd.Process.Kill(); err != nil {
					log.Printf("failed to kill process on signal: %v", err)
				}
			}
			return fmt.Errorf("signal caught: %v", sig)

		case err := <-monErr:
			if cmd.ProcessState == nil {
				if err := cmd.Process.Kill(); err != nil {
					log.Printf("failed to kill process on monitor error: %v", err)
				}
			}
			return err
		}
	}
}