Process (grim) reaper library for golang - this is useful for cleaning up zombie processes inside docker containers (which do not have an init process running as pid 1).
import reaper "github.com/ramr/go-reaper"
func main() {
// Start background reaping of orphaned child processes.
go reaper.Reap()
// Rest of your code ...
// Note: If you also manage processes within your code aka
// exec commands or include some code that does do that,
// please refer to the section titled
// "[Into The Woods]"(https://github.com/ramr/go-reaper#into-the-woods)
}
If you run a container without an init process (pid 1) which would normally reap zombie processes, you could well end up with a lot of zombie processes and eventually exhaust the max process limit on your system.
If you have a golang program that runs as pid 1, then this library allows the golang program to setup a background signal handling mechanism to handle the death of those orphaned children and not create a load of zombies inside the pid namespace your container runs in.
For basic usage, see the tl;dr section above. This should be the most commonly used route you'd need to take.
But for those that prefer to go down "the road less traveled", you can
control whether to disable pid 1 checks and/or control the options passed
to the wait4
(or waitpid
) system call by passing configuration to the
reaper and optionally get notified when child processes are reaped.
import reaper "github.com/ramr/go-reaper"
func main() {
config := reaper.Config{
Pid: 0,
Options: 0,
Debug: true,
DisablePid1Check: false,
StatusChannel: make(chan reaper.Status, 42),
// StatusChannel: nil,
}
// Start background reaping of orphaned child processes.
go reaper.Start(config)
// Only use this if you care about status notifications
// for reaped process (aka StatusChannel != nil).
go func() {
select {
case status, ok := <-config.StatusChannel:
if !ok {
return
}
// process status (reaper.Status)
}
}()
// Rest of your code ...
}
The Pid
and Options
fields in the configuration are the pid
and
options
passed to the linux wait4
system call.
See the man pages for the wait4 or waitpid system call for details.
And finally, this part is for those folks that want to go into the woods.
This could be required when you need to manage the processes you invoke inside
your code (ala with os.exec.Command*
or syscall.ForkExec
or any variants)
or basically include some libraries/code that need to do the same.
In such a case, it is better to run the reaper in a separate process as pid 1
and run your code inside a child process. This will still be part of the same
code base but just forked off so that the reaper runs inside a different
process ...
import "os"
import "syscall"
import reaper "github.com/ramr/go-reaper"
func main() {
// Use an environment variable REAPER to indicate whether or not
// we are the child/parent.
if _, hasReaper := os.LookupEnv("REAPER"); !hasReaper {
// Start background reaping of orphaned child processes.
go reaper.Reap()
// Note: Optionally add an argument to the end to more
// easily distinguish the parent and child in
// something like `ps` etc.
args := os.Args
// args := append(os.Args, "#kiddo")
pwd, err := os.Getwd()
if err != nil {
// Note: Better to use a default dir ala "/tmp".
panic(err)
}
kidEnv := []string{ fmt.Sprintf("REAPER=%d", os.Getpid()) }
var wstatus syscall.WaitStatus
pattrs := &syscall.ProcAttr{
Dir: pwd,
Env: append(os.Environ(), kidEnv...),
Sys: &syscall.SysProcAttr{Setsid: true},
Files: []uintptr{
uintptr(syscall.Stdin),
uintptr(syscall.Stdout),
uintptr(syscall.Stderr),
},
}
pid, _ := syscall.ForkExec(args[0], args, pattrs)
// fmt.Printf("kiddo-pid = %d\n", pid)
_, err = syscall.Wait4(pid, &wstatus, 0, nil)
for syscall.EINTR == err {
_, err = syscall.Wait4(pid, &wstatus, 0, nil)
}
// If you put this code into a function, then exit here.
os.Exit(0)
return
}
// Rest of your code goes here ...
} /* End of func main. */