//go:build linux

package main

import (
	"os"
	"os/exec"
	"strconv"
	"strings"
	"syscall"
)

// An engine runs in a process group of its own, so that stopping it stops everything it started (PyTorch workers).
func setProcGroup(c *exec.Cmd) { c.SysProcAttr = &syscall.SysProcAttr{Setpgid: true} }

func signalGroup(pgid int, kill bool) {
	sig := syscall.SIGTERM
	if kill {
		sig = syscall.SIGKILL
	}
	syscall.Kill(-pgid, sig)
}

// pauseGroup stops or continues every process of an engine (to slow it down for a part of each second).
func pauseGroup(pgid int, on bool) {
	sig := syscall.SIGCONT
	if on {
		sig = syscall.SIGSTOP
	}
	syscall.Kill(-pgid, sig)
}

// pgidOf is the process group of a process (0 if it cannot be read); field 5 of /proc/<pid>/stat, after the "(name)".
func pgidOf(pid int) int {
	b, err := os.ReadFile("/proc/" + strconv.Itoa(pid) + "/stat")
	if err != nil {
		return 0
	}
	s := string(b)
	i := strings.LastIndexByte(s, ')')
	if i < 0 {
		return 0
	}
	f := strings.Fields(s[i+1:]) // state ppid pgrp ...
	if len(f) < 3 {
		return 0
	}
	g, _ := strconv.Atoi(f[2])
	return g
}

func procCmdline(pid int) string {
	b, _ := os.ReadFile("/proc/" + strconv.Itoa(pid) + "/cmdline")
	return strings.ReplaceAll(string(b), "\x00", " ")
}