Bullet physics in a separate thread on Unity

BulletThreadingUnity.cs

using System;
using System.Collections.Generic;
using System.Diagnostics;
using System.Threading;
using BulletSharp;
using BulletSharp.Math;
using BulletUnity;
using UnityEngine;
using System.Collections;
using Debug = UnityEngine.Debug;

public class MultithreadingTest : MonoBehaviour {

    [SerializeField] private float _physicsTimeStep;
    [SerializeField] private Transform _renderableBody;

    private bool _isPhysicsRunning;
    private Stopwatch _stopwatch;
    private MotionState _bodyView;

	// Use this for initialization
	void Start () {
        _bodyView = new DefaultMotionState();

        _stopwatch = new Stopwatch();
        _stopwatch.Start();

	    _isPhysicsRunning = true;
        new Thread(() => {
            DiscreteDynamicsWorld physicsWorld;
            {
                //List<CollisionShape> CollisionShapes = new List<CollisionShape>();

                DefaultCollisionConfiguration CollisionConf = new DefaultCollisionConfiguration();
                CollisionDispatcher Dispatcher = new CollisionDispatcher(CollisionConf);

                DbvtBroadphase Broadphase = new DbvtBroadphase();

                physicsWorld = new DiscreteDynamicsWorld(Dispatcher, Broadphase, null, CollisionConf);
                physicsWorld.Gravity = new BulletSharp.Math.Vector3(0, -1, 0);
            }

            {
                const float mass = 1.0f;
                //Add a single cube
                BoxShape shape = new BoxShape(1f, 1f, 1f);
                BulletSharp.Math.Vector3 localInertia = BulletSharp.Math.Vector3.Zero;
                shape.CalculateLocalInertia(mass, out localInertia);
                RigidBodyConstructionInfo rbInfo = new RigidBodyConstructionInfo(mass, _bodyView, shape, localInertia);
                var body = new RigidBody(rbInfo);
                rbInfo.Dispose();
                Matrix st = Matrix.Translation(new BulletSharp.Math.Vector3(0f, 0f, 0f));
                body.WorldTransform = st;
                physicsWorld.AddRigidBody(body);
            }

            float fixedTimePassed = 0;
            while (_isPhysicsRunning) {
                var currentTime = _stopwatch.ElapsedMilliseconds / 1000f;
                var fixedDeltaTime = currentTime - fixedTimePassed;

                var totalStepsPerformed = physicsWorld.StepSimulation(fixedDeltaTime, 5, _physicsTimeStep);
                fixedTimePassed += _physicsTimeStep * totalStepsPerformed;

                //Debug.Log("physics tick at " + (deltaTime));
                var sleepIntervalInMs = ((int) (_physicsTimeStep * 1000)) / 4;
                Thread.Sleep(sleepIntervalInMs);
            }
        }).Start();
	}

    void OnDestroy() {
        _isPhysicsRunning = false;
    }
	
	// Update is called once per frame
	void Update () {
	    Matrix trans;
        _bodyView.GetWorldTransform(out trans);
	    _renderableBody.position = BSExtensionMethods2.ExtractTranslationFromMatrix(ref trans);
        _renderableBody.rotation = BSExtensionMethods2.ExtractRotationFromMatrix(ref trans);
	}
}