[.net 多线程] Interlocked实现CAS操作

Interlocked:为多个线程共享的变量提供原子操作。

Interlocked.Increment(ref value)	数值加一（原子性操作）
Interlocked.Decrement(ref value)	数值减一（原子性操作）
Interlocked.Exchange(ref value1, value2)	交换：把值2赋给值1；返回原值
Interlocked.CompareExchange(ref value1, value2, value3)	实现比较和交换两种功能：值1和值3比较，如果相同，把值2给值1，不相同则不作任何操作；返回原值（多用于判断条件）（示例3中会用到）

• 实现原子级运算

 int increament = ;
 Thread th1 = new Thread(() =>
 {
     for (int i = ; i < ; i++)
         Console.WriteLine($"th1 {Interlocked.Increment(ref increament)}");
 });

 Thread th2 = new Thread(() =>
 {
     for (int i = ; i < ; i++)
         Console.WriteLine($"th2 {Interlocked.Increment(ref increament)}");
 });

 Thread th3 = new Thread(() =>
 {
     for (int i = ; i < ; i++)
         Console.WriteLine($"th3 {Interlocked.Increment(ref increament)}");
 });

 Thread th4 = new Thread(() =>
 {
     for (int i = ; i < ; i++)
         Console.WriteLine($"th4 {Interlocked.Increment(ref increament)}");
 });

 th1.Start();
 th2.Start();
 th3.Start();
 th4.Start();
 Console.ReadKey();

实现递增计算

运行结果：

 int increament = ;
 Thread th1 = new Thread(() =>
 {
     for (int i = ; i < ; i++)
         //Console.WriteLine($"th1 {Interlocked.Increment(ref increament)}");
         Console.WriteLine($"th1 {increament++}");
 });

 Thread th2 = new Thread(() =>
 {
     for (int i = ; i < ; i++)
         //Console.WriteLine($"th2 {Interlocked.Increment(ref increament)}");
         Console.WriteLine($"th2 {increament++}");
 });

 Thread th3 = new Thread(() =>
 {
     for (int i = ; i < ; i++)
         //Console.WriteLine($"th3 {Interlocked.Increment(ref increament)}");
         Console.WriteLine($"th3 {increament++}");
 });

 Thread th4 = new Thread(() =>
 {
     for (int i = ; i < ; i++)
         //Console.WriteLine($"th4 {Interlocked.Increment(ref increament)}");
         Console.WriteLine($"th4 {increament++}");
 });

 th1.Start();
 th2.Start();
 th3.Start();
 th4.Start();
 Console.ReadKey();

非原子并行计算

• 模拟锁

用Exchange函数实现锁

         //0 for false, 1 for true.
         private static int usingResource = ;
         //A simple method that denies reentrancy.
         static bool UseResource()
         {
             //0 indicates that the method is not in use.
             if ( == Interlocked.Exchange(ref usingResource, ))
             {
                 Console.WriteLine("{0} acquired the lock", Thread.CurrentThread.Name);

                 //Code to access a resource that is not thread safe would go here.

                 //Simulate some work
                 Thread.Sleep();

                 Console.WriteLine("{0} exiting lock", Thread.CurrentThread.Name);

                 //Release the lock
                 Interlocked.Exchange(ref usingResource, );
                 return true;
             }
             else
             {
                 Console.WriteLine("   {0} was denied the lock", Thread.CurrentThread.Name);
                 return false;
             }
         }

用Exchange模拟锁

用CompareExchange函数实现锁

         private double totalValue = 0.0;

         public double Total { get { return totalValue; } }

         public double AddToTotal(double addend)
         {
             double initialValue, computedValue;
             do
             {
                 initialValue = totalValue;//---(1)
                 computedValue = initialValue + addend;//---(2)

             }
             while (initialValue != Interlocked.CompareExchange(ref totalValue,
                 computedValue, initialValue));
             //Interlocked.CompareExchange：比较totalValue与initialValue是否相同，如果相同，则用computedValue的值覆盖totalValue

             //如果totalValue与initialValue值不相同，则说明在（1）与（2）步骤执行的同时，
             //其他线程执行了对totalValue进行了改变
             return computedValue;
         }

CompareExchange模拟锁

原子操作参考：http://www.cnblogs.com/5iedu/p/4719625.html