`process`/`child_process`: be able to kill all descendent processes for a given process.

[tony-go]

Hi 👋,

Hope everyone is doing great.

Is your feature request related to a problem? Please describe.
I used require("child_process").spawn recently with the option shell: true.

I observe in this case that two processes are spawned on for the shell itself and another one for the current command spawned by the shell.

So when I use ChildProcess.kill(), it kills the shell process but not its child (descendent processes). (In my case the child process is an HTTP server, so a long process that doesn't exist itself")

Describe the solution you'd like
I thought about two different APIs:

• First one (with the ChildProcess)

const { spawn } = require("child_process");

const p1 = spawn(httpServerCommand, { shell: true });

p1.killDeep();

• Second one (with process)

const { spawn } = require("child_process");

const p1 = spawn(httpServerCommand, { shell: true });

process.killDeep(p1.pid);

In both cases killDeep will kill all the descendent processes.

Describe alternatives you've considered
I used this library: https://www.npmjs.com/package/tree-kill

I'm sorry in advance if I miss something in the documentation (But I promise that I tried ahahah)

If this feature request is acceptable, I could help and contribute (with a bit of guidance ^^)

Thanks for reading me.

[tniessen]

Thank you for the detailed issue, this is definitely a useful feature.

The problem that I usually come across when I try to implement something like this is that whether the proposed behavior is correct depends more on the spawned process tree than on the process that spawned the process (i.e., Node.js).

For example, which signal should kill which process? And how do we determine what processes to kill? And in what order? All this is highly OS specific and, unfortunately, often introduces race conditions.

On Linux, the kill function has a built-in feature to kill all processes belonging to a certain process group, which is great. However, not every subtree has its own process group:

├─gdm3(1132,1132)─┬─gdm-session-wor(1260,1132)─┬─gdm-x-session(1271,1271)─┬─Xorg(1273,1271)─┬─{Xorg}(1275,1271)
│                 │                            │                          │                 ├─{Xorg}(1276,1271)
│                 │                            │                          │                 ├─{Xorg}(1277,1271)

Here, there are seven processes with a depth of five but only two process groups.

I believe it is possible to kill process groups in Node.js using process.kill, but I am not entirely sure. And even if it works, it depends on the OS.

The tree-kill package determines PIDs by running an OS-specific shell command and then kills those PIDs. We could to that, however, this introduces race conditions since new processes might be spawned in-between those two steps. Even worse, in theory, after a process ends, the OS might reuse the same PID for a different process and tree-kill could, theoretically, end up killing the wrong process.

A "nice" process might react to SIGINT by killing its children using whatever signal is appropriate, but I realize that not all processes are designed to do that.

[tony-go]

Hi @tniessen 👋

Thanks a lot for this detailed answer and for you time. It's really nice that you shared you experience.

In fact, it's not safe at all 🙈 and seems a bit tricky.

I'll close this issue to avoid letting noise here ^^

This won't be my first be my first contribution 😁. If one day you want to spike on this, feel free to hit me ^^

[tniessen]

Let's keep it open for a few more days, maybe someone else wants to weigh in. This is a commonly used feature after all :)

[tony-go]

Thanks a lot @tniessen ^^