.net异步与多线程

一直不清楚异步与多线程的区别，不知道回调函数是在新线程还是原线程执行。
上网没查找到，自已研究。

using  System;
using  System.IO;
using  System.Threading;
namespace  test_异步
... {
    class Class1
    ...{
        [STAThread]
        static void Main(string[] args)
        ...{
            int i=0;
            FileStream fs=new FileStream(@"c:kk.txt",FileMode.Create,FileAccess.Write,FileShare.Write);
            fs.BeginWrite(new byte[]...{1},0,1,new AsyncCallback(endWrite),fs);
            while(true)...{
                System.Console.WriteLine("main_"+i++);
                Thread.Sleep(500);
            }
        }
        public static void endWrite(IAsyncResult ir)
        ...{
            ((FileStream)ir.AsyncState).Close();
            int i=0;
            while(true)
            ...{
                System.Console.WriteLine("endwrite_"+i++);
                Thread.Sleep(100);
            }
        }
    }
}

 上面的结果是每输出5个 endwrite_i 输出一个 main_i ，说明异步也是在不同线程中运行，和多线程没什么不同。
但是MSDN和网上的代码上很多代码都是在回调函数中再次调用异步函数，这样岂不是会产生很多进程？不过MSDN中都这样写也许不是这样，再次测试。

using  System;
using  System.IO;
using  System.Threading;
using  System.Runtime.InteropServices;

namespace  test_异步
... {
    class Class1
    ...{
        [DllImport("kernel32.dll")]  
        public static extern int GetCurrentThreadId();  
        [STAThread]
        static void Main(string[] args)
        ...{
            int i=0;
            FileStream fs=new FileStream(@"c:kk.txt",FileMode.Create,FileAccess.Write,FileShare.Write);
            fs.BeginWrite(new byte[]...{1},0,1,new AsyncCallback(endWrite),fs);
            while(true)...{
                System.Console.WriteLine("main_"+i++);
                Thread.Sleep(100);
            }
        }
        public static void endWrite(IAsyncResult ir)
        ...{
            Thread.Sleep(100);
            ((FileStream)ir.AsyncState).Close();
            FileStream fs=new FileStream(@"c:kk.txt",FileMode.Create,FileAccess.Write,FileShare.Write);
            fs.BeginWrite(new byte[]...{1},0,1,new AsyncCallback(endWrite),fs);
            System.Console.WriteLine("endwrite_"+GetCurrentThreadId());
        }
    }
}

输出结果：

 

main_0
main_1
endwrite_2264
main_2
endwrite_2264
main_3
endwrite_2264
main_4
endwrite_2264
main_5
endwrite_2356
main_6
endwrite_2356
main_7
endwrite_2356
main_8
endwrite_2356
main_9
endwrite_2264
endwrite_2356
endwrite_2264

可以看到产生线程的ＩＤ多是相同的，是使用了同一个线程还是线程结束后，新线程ＩＤ号相同？再次测试。

using  System;
using  System.IO;
using  System.Threading;
using  System.Runtime.InteropServices;

namespace  test_异步
... {
    class Class1
    ...{
        [DllImport("kernel32.dll")]  
        public static extern int GetCurrentThreadId();  
        [STAThread]
        static void Main(string[] args)
        ...{
            int i=0;
            FileStream fs=new FileStream(@"c:kk.txt",FileMode.Create,FileAccess.Write,FileShare.Write);
            fs.BeginWrite(new byte[]...{1},0,1,new AsyncCallback(endWrite),fs);
            while(i<100)...{
                System.Console.WriteLine("main_"+i++);
                Thread.Sleep(100);
            }
        }
        public static void endWrite(IAsyncResult ir)
        ...{
            ((FileStream)ir.AsyncState).Close();
            FileStream fs=new FileStream(@"c:kk.txt",FileMode.Create,FileAccess.Write,FileShare.Write);
            fs.BeginWrite(new byte[]...{1},0,1,new AsyncCallback(endWrite),fs);
            System.Console.WriteLine("endwrite_"+GetCurrentThreadId());
            Thread.Sleep(100);
        }
    }
}

结果输出：

main_98
endwrite_2204
endwrite_3884
endwrite_2280
endwrite_2216
endwrite_1632
endwrite_740
endwrite_3760
endwrite_4016
endwrite_1220
endwrite_1784
endwrite_4088
endwrite_3964
endwrite_2160
endwrite_2360
endwrite_2352
endwrite_912
endwrite_2376
endwrite_4048
endwrite_2364
endwrite_4076
endwrite_4008
endwrite_992
main_99
endwrite_2204
endwrite_3884
endwrite_2280
endwrite_2216
endwrite_1632
endwrite_740
endwrite_3760
endwrite_4016
endwrite_1220
endwrite_1784
endwrite_4088
endwrite_3964
endwrite_2160
endwrite_2360
endwrite_2352
endwrite_912
endwrite_2376
endwrite_4048
endwrite_2364
endwrite_4076
endwrite_4008
endwrite_992

结论：异步和多线程没有区别，有可能是经过优化后的多线程

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http://blog.youkuaiyun.com/xiyou/archive/2006/09/19/1245614.aspx