[.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 = 0;
Thread th1 = new Thread(() =>
{
    for (int i = 0; i < 10; i++)
        Console.WriteLine($"th1 {Interlocked.Increment(ref increament)}");
});

Thread th2 = new Thread(() =>
{
    for (int i = 0; i < 10; i++)
        Console.WriteLine($"th2 {Interlocked.Increment(ref increament)}");
});

Thread th3 = new Thread(() =>
{
    for (int i = 0; i < 10; i++)
        Console.WriteLine($"th3 {Interlocked.Increment(ref increament)}");
});

Thread th4 = new Thread(() =>
{
    for (int i = 0; i < 10; i++)
        Console.WriteLine($"th4 {Interlocked.Increment(ref increament)}");
});

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

运行结果：

int increament = 0;
Thread th1 = new Thread(() =>
{
    for (int i = 0; i < 10; i++)
        //Console.WriteLine($"th1 {Interlocked.Increment(ref increament)}");
        Console.WriteLine($"th1 {increament++}");
});

Thread th2 = new Thread(() =>
{
    for (int i = 0; i < 10; i++)
        //Console.WriteLine($"th2 {Interlocked.Increment(ref increament)}");
        Console.WriteLine($"th2 {increament++}");
});

Thread th3 = new Thread(() =>
{
    for (int i = 0; i < 10; i++)
        //Console.WriteLine($"th3 {Interlocked.Increment(ref increament)}");
        Console.WriteLine($"th3 {increament++}");
});

Thread th4 = new Thread(() =>
{
    for (int i = 0; i < 10; i++)
        //Console.WriteLine($"th4 {Interlocked.Increment(ref increament)}");
        Console.WriteLine($"th4 {increament++}");
});

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

• 模拟锁

用Exchange函数实现锁

        //0 for false, 1 for true.
        private static int usingResource = 0;
        //A simple method that denies reentrancy.
        static bool UseResource()
        {
            //0 indicates that the method is not in use.
            if (0 == Interlocked.Exchange(ref usingResource, 1))
            {
                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(500);

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

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

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;
        }

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