Snippet to allow using thread in Unity3d. This snippet including dependency, where should threading code be, and editor events detection to kill thread.

unity3d_thread_snippet.md

Dependencies

using System.Threading;
using UnityEditor;

Declare classes

Above the public class ScriptFileName : MonoBehaviour.

public enum PlayModeState
{
	Stopped,
	Playing,
	Paused
}

[InitializeOnLoad]
public class EditorPlayMode
{
	private static PlayModeState _currentState = PlayModeState.Stopped;
	
	static EditorPlayMode()
	{
		EditorApplication.playmodeStateChanged = OnUnityPlayModeChanged;
	}
	
	public static event Action<PlayModeState, PlayModeState> PlayModeChanged;
	
	public static void Play()
	{
		EditorApplication.isPlaying = true;
	}
	
	public static void Pause()
	{
		EditorApplication.isPaused = true;
	}
	
	public static void Stop()
	{
		EditorApplication.isPlaying = false;
	}
	
	
	private static void OnPlayModeChanged(PlayModeState currentState, PlayModeState changedState)
	{
		if (PlayModeChanged != null)
			PlayModeChanged(currentState, changedState);
	}
	
	private static void OnUnityPlayModeChanged()
	{
		var changedState = PlayModeState.Stopped;
		switch (_currentState)
		{
		case PlayModeState.Stopped:
			if (EditorApplication.isPlayingOrWillChangePlaymode)
			{
				changedState = PlayModeState.Playing;
			}
			break;
		case PlayModeState.Playing:
			if (EditorApplication.isPaused)
			{
				changedState = PlayModeState.Paused;
			}
			else
			{
				changedState = PlayModeState.Stopped;
			}
			break;
		case PlayModeState.Paused:
			if (EditorApplication.isPlayingOrWillChangePlaymode)
			{
				changedState = PlayModeState.Playing;
			}
			else
			{
				changedState = PlayModeState.Stopped;
			}
			break;
		default:
			throw new ArgumentOutOfRangeException();
		}
		
		// Fire PlayModeChanged event.
		OnPlayModeChanged(_currentState, changedState);
		
		// Set current state.
		_currentState = changedState;
	}
	
}

Inside the public class ScriptFileName : MonoBehaviour as fisrt class.

[InitializeOnLoad]
	public class SingleEntryPoint
	{
		static SingleEntryPoint()
		{
			Debug.Log("SingleEntryPoint. Up and running");
			EditorPlayMode.PlayModeChanged += OnPlayModeChanged;
		}

		private static void OnPlayModeChanged(PlayModeState currentMode, PlayModeState changedMode)
		{
			if(currentMode == PlayModeState.Playing && changedMode == PlayModeState.Stopped)
			{
				Debug.Log("Thread is killed! - Playing to Stopped");
				threadFlag = false;
			}
			if(currentMode == PlayModeState.Playing && changedMode == PlayModeState.Paused)
			{
				Debug.Log("Editor is paused.");
			}
			if(currentMode == PlayModeState.Stopped && changedMode == PlayModeState.Playing)
			{
				Debug.Log("Start playing");
			}
			if(currentMode == PlayModeState.Paused && changedMode == PlayModeState.Playing)
			{
				Debug.Log("Back to play again!");
			}
			if(currentMode == PlayModeState.Paused && changedMode == PlayModeState.Stopped)
			{
				Debug.Log("Thread is killed! - Pause to Stopped");
				threadFlag = false;
			}
		}
	}

Inside the public class ScriptFileName : MonoBehaviour as last class.

void OnApplicationQuit()
	{
		
		threadFlag = false;
		Debug.Log("2 "+threadFlag);
		
	}

Using thread

Declare threadFlag.

private static bool threadFlag = true;

Create method to run in another thread. This method will run endlessly until threadFlag is set to false.

private float needPosition;
private float finalPosition;

void doSomething()
	{   
		while(threadFlag)
		{
			needPosition = Sensor.readPosition();
			finalPosition = (needPosition * 1024)/18;
		}
	}

It is fine to call thread from start now!

void Start()
	{
		Thread readPosThread = new Thread(doSomething);
		readPosThread.Start();
	}