I am using GO to check if a process (not been parent) has ben terminated, basically something like the pwait command in FreeBSD but written in go.
Currently I am trying a for loop
with a kill -0
, but I notice that the CPU usage is very high 99% with this approach, here is the code:
package main
import (
"fmt"
"os"
"strconv"
"syscall"
"time"
)
func main() {
if len(os.Args) != 2 {
fmt.Printf("usage: %s pid", os.Args[0])
os.Exit(1)
}
pid, err := strconv.ParseInt(os.Args[1], 10, 64)
if err != nil {
panic(err)
}
process, err := os.FindProcess(int(pid))
err = process.Signal(syscall.Signal(0))
for err == nil {
err = process.Signal(syscall.Signal(0))
time.Sleep(500 * time.Millisecond)
}
fmt.Println(err)
}
Any idea of how to improve or properly implement this.
Thanks in advance.
UPDATE
Adding a sleep
within the loop like suggested, helps reducing the load.
From the provided links, seems to be possible to attach to the existing pid, I will give a try PtraceAttach but don't know if this may have side effects, any idea?
As suggested I was available to use kqueue:
package main
import (
"fmt"
"log"
"os"
"strconv"
"syscall"
)
func main() {
if len(os.Args) != 2 {
fmt.Printf("usage: %s pid", os.Args[0])
os.Exit(1)
}
pid, err := strconv.ParseInt(os.Args[1], 10, 64)
if err != nil {
panic(err)
}
process, _ := os.FindProcess(int(pid))
kq, err := syscall.Kqueue()
if err != nil {
fmt.Println(err)
}
ev1 := syscall.Kevent_t{
Ident: uint64(process.Pid),
Filter: syscall.EVFILT_PROC,
Flags: syscall.EV_ADD,
Fflags: syscall.NOTE_EXIT,
Data: 0,
Udata: nil,
}
for {
events := make([]syscall.Kevent_t, 1)
n, err := syscall.Kevent(kq, []syscall.Kevent_t{ev1}, events, nil)
if err != nil {
log.Println("Error creating kevent")
}
if n > 0 {
break
}
}
fmt.Println("fin")
}
Works fine, but wondering how to implement/achieve the same on linux since I think kqueue
not available on it, any ideas ?