System.dll中出现未处理的“System.Threading.SemaphoreFullException”类型异常

Question

System.dll中出现未处理的“System.Threading.SemaphoreFullException”类型异常 附加信息：将指定的计数添加到信号量将导致它超过其最大计数。

点击按钮

ThreadPool.SetMaxThreads(MAX_THREADS, MAX_THREADS);
semaphore = new System.Threading.Semaphore(MAX_THREADS, MAX_THREADS);

mainDownloadThread =  new Thread(() => startDownload(list));
mainDownloadThread.SetApartmentState(ApartmentState.STA);
mainDownloadThread.Start();

主线程在这里

void startDownload(List<string> list)
{

    manualResetEvent = new ManualResetEvent(false);

    foreach (string link in list)
    {

        ThreadInfo threadInfo = new ThreadInfo();
        threadInfo.Index = threadIndex++;
        threadInfo.link = link;
        threadInfo.ManualResetEvent = manualResetEvent;
        ThreadPool.QueueUserWorkItem(new WaitCallback(ProcessRequest), threadInfo);
        totalItems++;
    }
    manualResetEvent.WaitOne();
    base.BeginInvoke(new frmMain.EnableExportDelegate(this.enableInterface), null);

}

和processRequest

void processRequest(object obj)
{
    try
    {

        ThreadInfo threadInfo = obj as ThreadInfo;
        semaphore.WaitOne();
        manualResetEvent = threadInfo.ManualResetEvent;
        string link = threadInfo.link;

        if (isCancelled == true) return;
        if (manualResetEvent.WaitOne(0, false)) return;

        //stuff
        .
        .
        .
        .
        if (Interlocked.Decrement(ref this.totalItems) == 0 || isCancelled == true)
        {
            manualResetEvent.Set();
        }
    }
    catch
    {

    }
    finally
    {
        semaphore.Release();
        //////Exception thrown on above line//////
    }
}

不确定我是做对还是错，但是在点击上面的按钮后，它会抛出异常。