How do I use PhysicsDirectSpaceState while threading?

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How do I use PhysicsDirectSpaceState while threading?

KnightNine

Am I able to run functions like intersect_ray() from a thread without use of call_deferred()?

I am getting errors that I can only assume are the cause of my thread conflicting with the main thread, and they are inconsistent and happen at random:

ERROR: Condition "space->locked" is true. Returned: false
   at: PhysicsDirectSpaceStateSW::intersect_ray (servers\physics\space_sw.cpp:104) - Condition "space->locked" is true. Returned: false

i am fetching the direct space state from a physics_process() loop in my main node like this

var direct_space_state = Global_Variables_3D.world.phys_dir_space

and the loop looks like this:

func _physics_process(delta):
	phys_dir_space = get_world().direct_space_state

I am also actively using the same phys_dir_space var in my main thread so I assume this to be the cause of the errors.
the documentation says that I need to access the space state from _physics_process() to avoid this "locked" error, and yet I am still receiving it.

and here's the call stack from another seemingly physics related error that crashes my project.

ERROR: FATAL: Index p_index = 2 is out of bounds (count = 0).
   at: LocalVector<unsigned int,unsigned int,1>::operator [] (C:\Users\Alex\Desktop\Godot_v3.1.1-stable_mono_win64\godot master\godot\core/local_vector.h:181) - FATAL: Index p_index = 2 is out of bounds (count = 0).

================================================================
CrashHandlerException: Program crashed
Engine version: Godot Engine v3.5.1.rc.custom_build (46f4047d2a90e49f29d7098d9aa1eb3ba5a79981)
Dumping the backtrace. Please include this when reporting the bug on: https://github.com/godotengine/godot/issues

[0] LocalVector<unsigned int,unsigned int,1>::operator[] (C:\Users\User_Name\Desktop\Godot_v3.1.1-stable_mono_win64\godot master\godot\core\local_vector.h:181)
[1] LocalVector<unsigned int,unsigned int,1>::operator[] (C:\Users\User_Name\Desktop\Godot_v3.1.1-stable_mono_win64\godot master\godot\core\local_vector.h:181)
[2] BVH_Tree<CollisionObjectSW,2,2,128,BroadPhaseBVH::UserPairTestFunction<CollisionObjectSW>,BroadPhaseBVH::UserCullTestFunction<CollisionObjectSW>,1,AABB,Vector3>::_cull_translate_hits (C:\Users\User_Name\Desktop\Godot_v3.1.1-stable_mono_win64\godot master\godot\core\math\bvh_cull.inc:42)
[3] BVH_Tree<CollisionObjectSW,2,2,128,BroadPhaseBVH::UserPairTestFunction<CollisionObjectSW>,BroadPhaseBVH::UserCullTestFunction<CollisionObjectSW>,1,AABB,Vector3>::cull_segment (C:\Users\User_Name\Desktop\Godot_v3.1.1-stable_mono_win64\godot master\godot\core\math\bvh_cull.inc:116)
[4] BVH_Manager<CollisionObjectSW,2,1,128,BroadPhaseBVH::UserPairTestFunction<CollisionObjectSW>,BroadPhaseBVH::UserCullTestFunction<CollisionObjectSW>,AABB,Vector3,1>::cull_segment (C:\Users\User_Name\Desktop\Godot_v3.1.1-stable_mono_win64\godot master\godot\core\math\bvh.h:373)
[5] BroadPhaseBVH::cull_segment (C:\Users\User_Name\Desktop\Godot_v3.1.1-stable_mono_win64\godot master\godot\servers\physics\broad_phase_bvh.cpp:81)
[6] PhysicsDirectSpaceStateSW::intersect_ray (C:\Users\User_Name\Desktop\Godot_v3.1.1-stable_mono_win64\godot master\godot\servers\physics\space_sw.cpp:112)
[7] PhysicsDirectSpaceState::_intersect_ray (C:\Users\User_Name\Desktop\Godot_v3.1.1-stable_mono_win64\godot master\godot\servers\physics_server.cpp:259)
[8] MethodBind6R<PhysicsDirectSpaceState,Dictionary,Vector3 const &,Vector3 const &,Vector<RID> const &,unsigned int,bool,bool>::call (C:\Users\User_Name\Desktop\Godot_v3.1.1-stable_mono_win64\godot master\godot\core\method_bind_ext.gen.inc:415)
[9] Object::call (C:\Users\User_Name\Desktop\Godot_v3.1.1-stable_mono_win64\godot master\godot\core\object.cpp:918)
[10] Variant::call_ptr (C:\Users\User_Name\Desktop\Godot_v3.1.1-stable_mono_win64\godot master\godot\core\variant_call.cpp:1229)
[11] GDScriptFunction::call (C:\Users\User_Name\Desktop\Godot_v3.1.1-stable_mono_win64\godot master\godot\modules\gdscript\gdscript_function.cpp:1049)
[12] GDScriptInstance::call_multilevel (C:\Users\User_Name\Desktop\Godot_v3.1.1-stable_mono_win64\godot master\godot\modules\gdscript\gdscript.cpp:1211)
[13] Node::_notification (C:\Users\User_Name\Desktop\Godot_v3.1.1-stable_mono_win64\godot master\godot\scene\main\node.cpp:58)
[14] Node::_notificationv (C:\Users\User_Name\Desktop\Godot_v3.1.1-stable_mono_win64\godot master\godot\scene\main\node.h:47)
[15] Spatial::_notificationv (C:\Users\User_Name\Desktop\Godot_v3.1.1-stable_mono_win64\godot master\godot\scene\3d\spatial.h:52)
[16] Object::notification (C:\Users\User_Name\Desktop\Godot_v3.1.1-stable_mono_win64\godot master\godot\core\object.cpp:929)
[17] SceneTree::_notify_group_pause (C:\Users\User_Name\Desktop\Godot_v3.1.1-stable_mono_win64\godot master\godot\scene\main\scene_tree.cpp:1107)
[18] SceneTree::idle (C:\Users\User_Name\Desktop\Godot_v3.1.1-stable_mono_win64\godot master\godot\scene\main\scene_tree.cpp:608)
[19] Main::iteration (C:\Users\User_Name\Desktop\Godot_v3.1.1-stable_mono_win64\godot master\godot\main\main.cpp:2298)
[20] OS_Windows::run (C:\Users\User_Name\Desktop\Godot_v3.1.1-stable_mono_win64\godot master\godot\platform\windows\os_windows.cpp:3543)
[21] widechar_main (C:\Users\User_Name\Desktop\Godot_v3.1.1-stable_mono_win64\godot master\godot\platform\windows\godot_windows.cpp:176)
[22] _main (C:\Users\User_Name\Desktop\Godot_v3.1.1-stable_mono_win64\godot master\godot\platform\windows\godot_windows.cpp:198)
[23] main (C:\Users\User_Name\Desktop\Godot_v3.1.1-stable_mono_win64\godot master\godot\platform\windows\godot_windows.cpp:210)
[24] __scrt_common_main_seh (d:\a01\_work\20\s\src\vctools\crt\vcstartup\src\startup\exe_common.inl:288)
[25] BaseThreadInitThunk
-- END OF BACKTRACE --
================================================================

This fatal error happens right when the thread ends for some reason, even though there are no physics related calls happening then. I wonder if it's somehow related to the first error.

cybereality

What is the main thread in your app and where are you calling the physics state?

Pixophir

Interacting with the scene tree is not thread safe without precautions. There are many ways a threaded application can crash at vexing places, often connected to missing synchronisation, or the caller ending before a thread returned. A call_deferred() postpones execution until between frames. Asking for the outcome in the same script may also provoke a call to terminate().

It may be questioned if a single raycast merits pot-poning. This probably blocks more resources than just executing the raycast right away. But then again, idk your use case.

cybereality

Can you also explain more about your app and what you are using threading for? The use case is not clear to me. From what I understand, the physics engine is single-threaded. I think there is some work for multithreading, but I'm not sure that is finished yet, or maybe Godot 4.0 only. If it is single-threaded, then I don't think you would see any performance boost from querying in different threads, in fact it might be a loss or cause the weird problems you are seeing. It might be a better idea to keep the physics functions and ray casts to the main thread.