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@partho222
Forked from wrfly/fork_and_daemon.go
Created March 19, 2023 13:13
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golang fork and exec and handle signals
package main
import (
"flag"
"fmt"
"log"
"os"
"os/signal"
"syscall"
)
var (
daemon bool
fork int
children = []int{}
)
func init() {
flag.BoolVar(&daemon, "daemon", false, "run as daemon")
flag.IntVar(&fork, "fork", 0, "fork how many sub process")
flag.Parse()
}
func main() {
pid := os.Getpid()
ppid := os.Getppid()
log.Printf("pid: %d, ppid: %d, args: %s", pid, ppid, os.Args)
// handle exit for every process
go func() {
sig := make(chan os.Signal)
signal.Notify(sig)
for s := range sig {
// see https://u.kfd.me/33
// SIGINT means graceful stop
// SIGTERM means graceful [or not], cleanup something
// SIGQUIT SIGKILL means immediately shutdown
if s == syscall.SIGQUIT || s == syscall.SIGTERM {
log.Printf("[%d] exit\n", pid)
// make sure that parent can send signals to the children
for _, child := range children {
log.Printf("parent send %s to %d", s, child)
syscall.Kill(child, s.(syscall.Signal))
}
syscall.Exit(0)
}
}
}()
// only the parent process can do
if _, isChild := os.LookupEnv("CHILD_ID"); !isChild {
if daemon {
if _, isDaemon := os.LookupEnv("DAEMON"); !isDaemon {
daemonENV := []string{"DAEMON=true"}
childPID, _ := syscall.ForkExec(os.Args[0], os.Args,
&syscall.ProcAttr{
Env: append(os.Environ(), daemonENV...),
Sys: &syscall.SysProcAttr{
Setsid: true,
},
Files: []uintptr{0, 1, 2}, // print message to the same pty
})
log.Printf("process %d run as daemon, %d will exit", childPID, pid)
return // this return will give back the pty
}
log.Printf("daemon %d running and won't fork another daemon", os.Getpid())
}
for i := 0; i < fork; i++ {
args := append(os.Args, fmt.Sprintf("#child_%d_of_%d", i, os.Getpid()))
childENV := []string{
fmt.Sprintf("CHILD_ID=%d", i),
}
pwd, err := os.Getwd()
if err != nil {
log.Fatalf("getwd err: %s", err)
}
childPID, _ := syscall.ForkExec(args[0], args, &syscall.ProcAttr{
Dir: pwd,
Env: append(os.Environ(), childENV...),
Sys: &syscall.SysProcAttr{
Setsid: true,
},
Files: []uintptr{0, 1, 2}, // print message to the same pty
})
log.Printf("parent %d fork %d", pid, childPID)
if childPID != 0 {
children = append(children, childPID)
}
}
// print children
log.Printf("parent: PID=%d children=%v", pid, children)
if len(children) == 0 && fork != 0 {
log.Fatalf("no child avaliable, exit")
}
// set env
for _, childID := range children {
if c := os.Getenv("CHILDREN"); c != "" {
os.Setenv("CHILDREN", fmt.Sprintf("%s,%d", c, childID))
} else {
os.Setenv("CHILDREN", fmt.Sprintf("%d", childID))
}
}
go func() {
// parent will [only] notify children
sig := make(chan os.Signal)
signal.Notify(sig)
for s := range sig {
for _, child := range children {
log.Printf("parent send %s to %d", s, child)
syscall.Kill(child, s.(syscall.Signal))
}
}
}()
}
// main
sig := make(chan os.Signal)
signal.Notify(sig)
for s := range sig {
log.Printf("PID[%d] got sig %s", pid, s)
}
}
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