C#中的异步多线程1 同步和异步对比

C#中的异步多线程1 同步和异步对比

同步版本示例：

namespace SyncSample{ class MyDownloadString {  Stopwatch sw = new Stopwatch();  public void DoRun()  {   const int LargeNumber = 6000000;   sw.Start();   //网络任务   int t1 = CountCharacters(1, "https://www.baidu.com");   int t2 = CountCharacters(2, "https://www.sogou.com/");   //本机任务   CountToALargeNumber(1, LargeNumber);   CountToALargeNumber(2, LargeNumber);   CountToALargeNumber(3, LargeNumber);   CountToALargeNumber(4, LargeNumber);   Console.WriteLine("Chars in Baidu:{0}", t1);   Console.WriteLine("Chars in Sougou:{0}", t2);  }  private int CountCharacters(int id, string url)  {   WebClient wc1 = new WebClient();   Console.WriteLine("Starting call {0}:{1,4:N0} ms", id, sw.Elapsed.TotalMilliseconds);   string result = wc1.DownloadString(new Uri(url));   Console.WriteLine("call {0} completed:{1,4:N0} ms", id, sw.Elapsed.TotalMilliseconds);   return result.Length;  }  private void CountToALargeNumber(int id, int value)  {   for (long i = 0; i < value; i++) ;   Console.WriteLine("End counting {0}:{1,4:N0} ms", id, sw.Elapsed.TotalMilliseconds);  } } class Program {  static void Main(string[] args)  {   MyDownloadString ds = new MyDownloadString();   ds.DoRun();   Console.ReadLine();   //同步时，会按照如下顺序执行 t1-t2-count1-count2-count3-count4，最耗时的任务发生在等待网站数据（starting call-call completed）的过程   //但如果能够在等待的过程中就执行count1-4就会极大节省时间  } }}

耗时为：

Starting call 1: 0 ms
call 1 completed: 222 ms
Starting call 2: 222 ms
call 2 completed: 435 ms
End counting 1: 448 ms
End counting 2: 460 ms
End counting 3: 473 ms
End counting 4: 486 ms
Chars in Baidu:14462
Chars in Sougou:19466

对应异步示例：

 class MyDownLoadString {  Stopwatch sw = new Stopwatch();  public void DoRun()  {   const int LargeNumber = 600000;   sw.Start();   Task<int> t1 = CountCharactersAsync(1, "https://www.baidu.com");   Task<int> t2 = CountCharactersAsync(2, "");   CountToALargeNumber(1, LargeNumber);   CountToALargeNumber(2, LargeNumber);   CountToALargeNumber(3, LargeNumber);   CountToALargeNumber(4, LargeNumber);   Console.WriteLine("Chars in Baidu:{0}", t1.Result);   Console.WriteLine("Chars in Sougou:{0}", t2.Result);  }  private async Task<int> CountCharactersAsync(int id, string site)  {   WebClient wc = new WebClient();   Console.WriteLine("Starting call {0}:{1,4:N0} ms", id, sw.Elapsed.TotalMilliseconds);   string result = await wc.DownloadStringTaskAsync(new Uri(site));   Console.WriteLine("Call {0} completed:{1,4:N0} ms", id, sw.Elapsed.TotalMilliseconds);   return result.Length;  }  private void CountToALargeNumber(int id,int value)  {   for (long i = 0; i < value; i++) ;   Console.WriteLine("End counting {0}:{1,4:N0} ms", id, sw.Elapsed.TotalMilliseconds);  } } class Program {  static void Main(string[] args)  {   MyDownLoadString ds = new MyDownLoadString();   ds.DoRun();   Console.ReadLine();   //对于耗时的网络任务，修改成了异步执行的方式，于是任务执行演变成了t1 start,t2 start-count1-4-t1 completed/t2 completed   //在等待网络任务的同时，完成了本机任务   //而这些任务，都是在主线程完成，并没有创建其他线程  } }

耗时为：

Starting call 1: 1 ms
Starting call 2: 58 ms
End counting 1: 62 ms
End counting 2: 63 ms
End counting 3: 64 ms
End counting 4: 65 ms
Call 2 completed: 199 ms
Call 1 completed: 243 ms
Chars in Baidu:14462
Chars in Sougou:16597

可见有效的压缩了时间，这是因为4次CountToALargeNumber都是在等待网站响应的过程中完成的，而这些工作都是在主线程完成的，并没有创建额外的线程。