从0自学C#13–子类和父类方法的锁对象问题

调用父类方法时，如何与子类方法，在锁对象不是同一个实例下，能线程安全，请见下面三种情况。

case1：

如下代码，在调用父类的方法时，和子类的方法，发生线程安全问题。原因的锁对象的实例不是同一个。

using System;using System.Collections.Generic;using System.Linq;using System.Text;using System.Threading.Tasks;using System.Threading;namespace ForTest//check the lock object for thread safety{    class Program    {        static void Main(string[] args)        {            son myson = new son();            Parallel.For(0, 5, (int i) =>             {                 myson.methodA();                 myson.methodC();             });            Console.ReadKey();        }    }    public class grandfather    {        //protected static object syncRoot = new object();    }    public class father:grandfather    {        private static object syncRoot = new object();        protected int cont = 0;        public virtual bool methodA()        {            lock (syncRoot)            {                cont++;                Thread.Sleep(1000);                Console.WriteLine("cout++ is " + cont);                return true;            }        }        public virtual bool methodB()        {            lock (syncRoot)            {                return true;            }        }    }    public class son:father    {        private static object syncRoot = new object();        public bool methodC()        {            lock (syncRoot)            {                cont += 2;                Thread.Sleep(2000);                Console.WriteLine("cont += 2 is " + cont);                return true;            }        }    }}

输出：

cout++ is 1cout++ is 4cont += 2 is 5cout++ is 5cout++ is 8cont += 2 is 9cout++ is 11cont += 2 is 11cont += 2 is 13cont += 2 is 15

case2：

case1的解决方法是，在父类初始化锁对象，让子类继承。这样就线程安全了。如下。

using System;using System.Collections.Generic;using System.Linq;using System.Text;using System.Threading.Tasks;using System.Threading;namespace ForTest//check the lock object for thread safety{    class Program    {        static void Main(string[] args)        {            son myson = new son();            Parallel.For(0, 5, (int i) =>             {                 myson.methodA();                 myson.methodC();             });            Console.ReadKey();        }    }    public class grandfather    {        protected static object syncRoot = new object();    }    public class father:grandfather    {        protected int cont = 0;        public virtual bool methodA()        {            lock (syncRoot)            {                cont++;                Thread.Sleep(1000);                Console.WriteLine("cout++ is " + cont);                return true;            }        }        public virtual bool methodB()        {            lock (syncRoot)            {                return true;            }        }    }    public class son:father    {        public bool methodC()        {            lock (syncRoot)            {                cont += 2;                Thread.Sleep(2000);                Console.WriteLine("cont += 2 is " + cont);                return true;            }        }    }}

输出：

cout++ is 1cout++ is 2cont += 2 is 4cout++ is 5cout++ is 6cout++ is 7cont += 2 is 9cont += 2 is 11cont += 2 is 13cont += 2 is 15

case3：

当然有些特殊情况下，子类硬要重新实例化一个锁对象。如何避免上面第一种线程安全问题发生？需要：

子类加锁重写父类分方法（如果父类methodA是虚方法）

或者

new一下（如果父类methodA是实例方法）。

using System;using System.Collections.Generic;using System.Linq;using System.Text;using System.Threading.Tasks;using System.Threading;namespace ForTest//check the lock object for thread safety{    class Program    {        static void Main(string[] args)        {            son myson = new son();            Parallel.For(0, 5, (int i) =>             {                 myson.methodA();                 myson.methodC();             });            Console.ReadKey();        }    }    public class grandfather    {        protected static object syncRoot = new object();    }    public class father:grandfather    {        protected int cont = 0;        public virtual bool methodA()        {            lock (syncRoot)            {                cont++;                Thread.Sleep(1000);                Console.WriteLine("cout++ is " + cont);               <em style="color:transparent">本文来源gao.dai.ma.com搞@代*码#网</em> return true;            }        }        public virtual bool methodB()        {            lock (syncRoot)            {                return true;            }        }    }    public class son:father    {        private static object sync = new object();        public override bool methodA()//重写        {            lock (sync)            {                return base.methodA();            }        }        public bool methodC()        {            lock (sync)            {                cont += 2;                Thread.Sleep(2000);                Console.WriteLine("cont += 2 is " + cont);                return true;            }        }    }}

或

 public new bool methodA()\\new一下        {            lock (sync)            {                return base.methodA();            }        }

输出：

cout++ is 1cout++ is 2cont += 2 is 4cout++ is 5cout++ is 6cout++ is 7cont += 2 is 9cont += 2 is 11cont += 2 is 13cont += 2 is 15

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