ThreadPoolTest.cs

using UnityEngine;
using System.Collections;
using System.Threading;

// Reference: http://www.dotnetperls.com/threadpool
// Usage: Attach this script to gameobject in scene, press play, hit 1 key to queue new threads, see console for progress

// we pass thread parameters as object
namespace UnityLibrary
{
    class ThreadInfo
    {
        public int threadIndex;
        public Vector3 myVector;
    }


    public class ThreadPoolTest : MonoBehaviour
    {
        int maxThreads = 2; // set your max threads here

        static readonly object _countLock = new object();
        static int _threadCount = 0;
        static bool closingApp = false;

        int clickCounter = 0;

        void Update()
        {
            // press 1 to spawn thread(s)
            if (Input.GetKeyDown(KeyCode.Alpha1))
            {
                // Pass these values to the thread.
                ThreadInfo threadData = new ThreadInfo();
                threadData.myVector = Random.insideUnitSphere * 10; // get some random vector3 value
                threadData.threadIndex = ++clickCounter;
                print("Queue new thread #" + threadData.threadIndex);
                ThreadPool.QueueUserWorkItem(new WaitCallback(MyWorkerThread), threadData);
            }
        }

        private void MyWorkerThread(System.Object a)
        {
            // Constrain the number of worker threads, loop here until less than maxthreads are running
            while (!closingApp)
            {
                // Prevent other threads from changing this under us
                lock (_countLock)
                {
                    if (_threadCount < maxThreads && !closingApp)
                    {
                        // Start processing
                        _threadCount++;
                        break;
                    }
                }
                Thread.Sleep(50);
            }

            if (closingApp) return;

            // we are ready to work now, prepare object that contains necessary info for the thread
            ThreadInfo threadInfo = a as ThreadInfo;
            Vector3 myVector = threadInfo.myVector;
            int myIndex = threadInfo.threadIndex;
            print("---From thread #" + myIndex + " processing myVector " + myVector);

            // for testing we just sleep here (you could do your heavy calculations here)
            Thread.Sleep(5000);

            // add this to your heavy work loop, so the thread quits if scene is closed
            //if (closingApp) return;

            print("---Finished thread #" + myIndex);

            // decrease thread counter, so other threads can start
            _threadCount--;
        }

        // set bool to close threads on exit
        void OnDestroy()
        {
            closingApp = true;
        }

    }
}