OS.execute without blocking mode causes zombie processes (defunct)

[rennomarcus]

Godot version

3.3.2

System information

Ubuntu 20.04.2 LTS, 64-bit

Issue description

When executing OS.execute with the blocking flag as false the process stays in zombie mode.

Because the process is already 'dead' I cannot kill it, thus remove from the process list.

Steps to reproduce

1. run any command in OS.execute with the flag blocking as false. Example: var pid = OS.execute('pwd', [], false)
2. go to your terminal and look for your processes and grep by keyword 'defunct'. Example: ps cax | grep defunct

You will see a list of processes executed by godot. If you keep running the command the list keeps growing. When you exit the application/game the processes are removed.

Minimal reproduction project

No response

[qrrk]

I ran into the same issue today. I start extracting an archive using tar, then sit in a loop checking if this process is still running (using ps, this time in blocking mode) before doing something with the extracted files. Well, with this issue the process never terminates, so that doesn't work. I'll try working around it using threads or maybe multiple nodes and signals, and post the results.

UPD. From my test project:

func _is_process_running(pid: int) -> bool:
	
	var exit_code = OS.execute("ps", ["-p", pid])
	return !exit_code


func _on_Button3_pressed() -> void:
	
	var fname = "REDACTED.tar.gz"
	var workdir = OS.get_executable_path().get_base_dir() + "/"
	var args = ["xzf", workdir + fname, "-C", workdir]
	
	var pid = OS.execute("tar", args, false)
	
	while _is_process_running(pid):
		yield(get_tree().create_timer(0.1), "timeout")
		
	print("Finished extracting ", fname)

[qrrk]

This will do the trick:

class_name OSExecWrapper
extends Object


signal process_exited

var _worker: Thread
var output = []
var exit_code = null


func _wrapper(path_and_args: Array) -> void:
	
	exit_code = OS.execute(path_and_args[0], path_and_args[1], true, output)
	emit_signal("process_exited")
	_worker.call_deferred("wait_to_finish")

func execute(path: String, args: PoolStringArray) -> void:
	
	_worker = Thread.new()
	_worker.start(self, "_wrapper", [path, args])

Usage example:

func _on_Button5_pressed() -> void:
	
	var oew = OSExecWrapper.new()
	print("Starting.")
	oew.execute("sh", ["-c", "sleep 1; ls /tmp"])
	yield(oew, "process_exited")
	print("Finished. Exit code: %s, output:\n%s" % [oew.exit_code, oew.output[0]])

[rsubtil]

For 4.0 this has been fixed by #44514