using System.Threading;
...

Thread t = new Thread(new ThreadStart(delegate
{
        Proxy(delegate
        {
                button3.Enabled = false;
        });

        ...
}));
t.IsBackground = true;
t.Start();

#region 多线程委托

public delegate void ProxyInvoker();

// 主线程直接执行，后台线程委托主线程执行
private void Proxy(ProxyInvoker invoke)
{
        if (invoke == null)
                return;

        if (this.InvokeRequired)
        {
                this.Invoke(invoke);
                return;
        }

        invoke();
}

#endregion

using System.Threading.Tasks;
...

// 限制执行线程数量
ParallelOptions parallelOption = new ParallelOptions();
parallelOption.MaxDegreeOfParallelism = 100;
object locker = new object();
Parallel.ForEach<string>(strList, parallelOption, str =>
{
        lock (locker)
        {
                // Do something...
        }
});