Allow access to PhysicsDirectSpaceState3D from outside the main thread.

[DAShoe1]

Tested versions

This issue is present when using a physics engine module such as GodotPhysics or the new JoltPhysics module.
This is not an issue when using Jolt physics as a GDExtension.

System information

Windows 11

Issue description

The following code prevents access to the PhysicsDirectSpaceState3D outside of the main thread,

redot-engine/servers/physics_server_3d_wrap_mt.h

Lines 116 to 120 in da61fa2

	// this function only works on physics process, errors and returns null otherwise
	PhysicsDirectSpaceState3D *space_get_direct_state(RID p_space) override {
	ERR_FAIL_COND_V(!Thread::is_main_thread(), nullptr);
	return physics_server_3d->space_get_direct_state(p_space);
	}

I don't believe this check is necessary as there is another check later that verifies that the space state is available,

redot-engine/modules/jolt_physics/jolt_physics_server_3d.cpp

Lines 233 to 239 in da61fa2

	PhysicsDirectSpaceState3D *JoltPhysicsServer3D::space_get_direct_state(RID p_space) {
	JoltSpace3D *space = space_owner.get_or_null(p_space);
	ERR_FAIL_NULL_V(space, nullptr);
	ERR_FAIL_COND_V_MSG((on_separate_thread && !doing_sync) || space->is_stepping(), nullptr, "Space state is inaccessible right now, wait for iteration or physics process notification.");
	return space->get_direct_state();
	}

Removing the main thread check in a custom build allows my project to work with the integrated Jolt physics module just as it does with the GDExtension version.

Steps to reproduce

Attempt a raycast from a thread or from a node running on a sub thread group.

Minimal reproduction project (MRP)

N/A

[Spartan322]

Do you know if this issue has been reported to Godot?

[DAShoe1]

I reported it here, godotengine/godot#103383.

[Arctis-Fireblight]

Discussions for this issue on the Godot side seem to believe this is a safe operation and unnecessary check.
We'll investigate this further in 26.4. If it really ends up being unnecessary I'll remove it.