Game hangs when calling load from a thread

[jbpuryear]

Godot version

3.4-1

System information

Arch Linux 5.15.5.arch1-1

Issue description

Game sometimes hangs when calling load from a thread, then calling wait_to_finish. I'm not sure, but I think it specifically happens when loading a resource that's not already in the cache. Adding a pause in the thread before the call to load with something like yield(get_tree().create_timer(0.001), "timeout") keeps the game from hanging, so I'm guessing it's some sort of mutex, race condition problem?

Possibly the same issue as #51225

Steps to reproduce

Add the following script to a node and set the file_path property to a resource not in the cache.

extends Node2D

export (String, FILE) var file_path

func _ready():
  var thread = Thread.new()
  thread.start(self, "hang_on_load", file_path)
  thread.wait_to_finish()

func hang_on_load(path):
#  Loading will work if you uncomment this line
#  yield(get_tree().create_timer(0.0001), "timeout")
  return load(path)

Minimal reproduction project

thread_loading_bug.zip