BeginInvoke、ThreadPool、Task三类异步方法的区别和速度比较

1. 如ThreadPool.UnsafeQueueUserWorkItem(()=>result=Add(1,2));
2. 用Task<>
3. 里面在程序末尾EventWaitHandle.Set()，外面WaitOne(TimeSpan)。
4. 获得BeginInvoke的返回值asyncResult，再调asyncResult.AsyncWaitHandle.WaitOne();

有图有真相。这是各种异步方法循环调用N次所需的时间。

代码如下：

     static void Main(string[] args)
        {
            Action threadStart = (() => { });
            WaitCallback waitCallback = new WaitCallback(a => { });
            Stopwatch stopWatch = new Stopwatch();

            stopWatch.Reset();
            stopWatch.Start();
            for (int i = 0; i < 10000; i++)
            {
                System.Threading.ThreadPool.UnsafeQueueUserWorkItem(waitCallback, null);
            }
            stopWatch.Stop();
            Console.WriteLine("{0,-40}{1}", "ThreadPool.UnsafeQueueUserWorkItem():", stopWatch.ElapsedTicks);
            GC.Collect();

            stopWatch.Reset();
            stopWatch.Start();
            for (int i = 0; i < 10000; i++)
            {
                System.Threading.ThreadPool.QueueUserWorkItem(waitCallback);
            }
            stopWatch.Stop();
            Console.WriteLine("{0,-40}{1}", "ThreadPool.QueueUserWorkItem():", stopWatch.ElapsedTicks);
            GC.Collect();

            stopWatch.Reset();
            stopWatch.Start();
            for (int i = 0; i < 10000; i++)
            {
                Task t = new Task(threadStart);
                t.Start();
            }
            stopWatch.Stop();
            Console.WriteLine("{0,-40}{1}", "Task():", stopWatch.ElapsedTicks);
            GC.Collect();

            stopWatch.Reset();
            stopWatch.Start();
            for (int i = 0; i < 10000; i++)
            {
                threadStart.BeginInvoke(null, null);
            }
            stopWatch.Stop();
            Console.WriteLine("{0,-40}{1}", "Delegate.BeinInvoke():", stopWatch.ElapsedTicks);

        } 

注意，上面BeginInvoke的用法并不完整，应当再调用EndInvoke。但是鉴于BeginInvoke已经最慢了，EndInvoke便不加了。

所以，如果无需返回值，一般就用ThreadPool吧，要更多控制，就Task。鄙人想不到用BeginInvoke的时机。