Stdio blocks main thread despite running in another thread.

Help Programming
,
1

I’m using Godot 4.4 and try to read the console output from a process I run, but for whatever reason it blocks my main thread no matter what I do. What’s going on?

func _running(exec):
	while OS.is_process_running(exec.pid): 
		var content = exec.stdio.get_as_text().strip_edges()
		if content:
			print(content)
	
func start() -> void:
	if _thread == null:
		var exec = OS.execute_with_pipe(OS.get_executable_path(), ["--instance", "--identifier", _id], false)
		_thread = Thread.new()
		_thread.start(_running.bind(exec))

If I don’t start the thread everything runs fine, but as soon as I start reading stdio everything freezes.

2

There is an odd snippet in the docs

If blocking is false, created pipes work in non-blocking mode, i.e. read and write operations will return immediately. Use FileAccess.get_error() to check if the last read/write operation was successful.

That print call in the thread could be thrashing on the main threads stream buffer. I would probably slow the thread down with a delay, or wait till you have actual string data. Or call deferred on print but again dont do it every cycle. Delay the thread.

3

This lead me to the real solution, it was calling exec.stdio on every loop, changing it to _thread.start(_running.bind(exec.pid, exec.stdio)) fixed the issue.

But I did change the _running too

func _running(pid, stdio: FileAccess):
	while OS.is_process_running(pid): 
		if stdio.get_length() > 0:
			print(stdio.get_line().strip_edges())