multithreading - C# Update ProgressBar from Thread -

i have windows form in xaml contains progress bars. threads spawned, jobs run, , status of jobs shown progress bars.

it's working ok, want limit number of jobs can run @ 1 time.

    protected int executingthreads = 0;     int maxthreadcount = 3;     object lockobj = new object();      public virtual void start()     {         inqueue = new queue<xelement>();          loadqueue();          while (inqueue.count != 0)         {             xelement request = inputqueue.dequeue();              system.threading.threadpool.queueuserworkitem(new system.threading.waitcallback(dowork), request);   /*         lock (lockobj)             {                 executingthreads++;                 while (executingthreads == maxthreadcount)                     thread.sleep(1);             }  */         }  /*         while (executingthreads != 0)             thread.sleep(1);  */      } 

to limit number of jobs running @ 1 time, added code that's shown here commented out lock , sleep. seems limit number of jobs running @ 1 time , jobs complete successfully.

but progressbar no longer incrementally displaying updates -- until jobs finish , shown completed. assume sleep prevents progressbar ui refresh. how can fix that? solution application.doevents() ?