《Advanced .NET Debugging》 读书笔记 Listing 6-4: Deadlock的简单示例

using System;
using System.Text;
using System.Threading;

namespace Advanced.NET.Debugging.Chapter6
{
    internal class DBWrapper1
    {
        private string connectionString;

        public DBWrapper1(string conStr)
        {
            this.connectionString = conStr;
        }
    }

    internal class DBWrapper2
    {
        private string connectionString;

        public DBWrapper2(string conStr)
        {
            this.connectionString = conStr;
        }
    }
   
    class Deadlock
    {
        private static DBWrapper1 db1;
        private static DBWrapper2 db2;

        static void Main(string[] args)
        {
            db1 = new DBWrapper1("DBCon1");
            db2 = new DBWrapper2("DBCon2");

            Thread newThread = new Thread(ThreadProc);
            newThread.Start();

            Thread.Sleep(2000);
            lock (db2)
            {
                Console.WriteLine("Updating DB2");
                Thread.Sleep(2000);
                lock (db1)
                {
                    Console.WriteLine("Updating DB1");
                }
            }
        }

        private static void ThreadProc()
        {
            Console.WriteLine("Start worker thread");
            lock (db1)
            {
                Console.WriteLine("Updating DB1");
                Thread.Sleep(3000);
                lock (db2)
                {
                    Console.WriteLine("Updating DB2");
                }
            }
            Console.WriteLine("Out");
        }
    }
}

Main函数线程会先sleep2秒，然后锁定db2对象，接着休息2秒，再试图锁定db1对象。而此时，db1对象已经被锁定，会在sleep3秒以后尝试锁定db2。现在的结果就是main线程拿不到db1，因为db1被ThreadProc线程占据，Main线程进入suspend状态；ThreadProc线程拿不到db2，因为db2被main线程占据,ThreadProc线程也进入了suspend状态。此时两个线程都进入了suspend状态，程序无法继续。

1. 在WinDbg下载入 Deadlock.exe

2. 在程序运行运行几秒进入思索状态以后，执行 .loadby sos.dll mscorwks

3. 载入 .load sosex.dll

4. 执行 !dlk

可见此时线程0x1占有db2，试图获取db1； 线程0x3占有db1， 试图占有db2。与分析符合。