[.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
 1 int increament = 0;
 2 Thread th1 = new Thread(() =>
 3 {
 4     for (int i = 0; i < 10; i++)
 5         Console.WriteLine($"th1 {Interlocked.Increment(ref increament)}");
 6 });
 7 
 8 Thread th2 = new Thread(() =>
 9 {
10     for (int i = 0; i < 10; i++)
11         Console.WriteLine($"th2 {Interlocked.Increment(ref increament)}");
12 });
13 
14 Thread th3 = new Thread(() =>
15 {
16     for (int i = 0; i < 10; i++)
17         Console.WriteLine($"th3 {Interlocked.Increment(ref increament)}");
18 });
19 
20 Thread th4 = new Thread(() =>
21 {
22     for (int i = 0; i < 10; i++)
23         Console.WriteLine($"th4 {Interlocked.Increment(ref increament)}");
24 });
25 
26 th1.Start();
27 th2.Start();
28 th3.Start();
29 th4.Start();
30 Console.ReadKey();
实现递增计算

运行结果：

 1 int increament = 0;
 2 Thread th1 = new Thread(() =>
 3 {
 4     for (int i = 0; i < 10; i++)
 5         //Console.WriteLine($"th1 {Interlocked.Increment(ref increament)}");
 6         Console.WriteLine($"th1 {increament++}");
 7 });
 8 
 9 Thread th2 = new Thread(() =>
10 {
11     for (int i = 0; i < 10; i++)
12         //Console.WriteLine($"th2 {Interlocked.Increment(ref increament)}");
13         Console.WriteLine($"th2 {increament++}");
14 });
15 
16 Thread th3 = new Thread(() =>
17 {
18     for (int i = 0; i < 10; i++)
19         //Console.WriteLine($"th3 {Interlocked.Increment(ref increament)}");
20         Console.WriteLine($"th3 {increament++}");
21 });
22 
23 Thread th4 = new Thread(() =>
24 {
25     for (int i = 0; i < 10; i++)
26         //Console.WriteLine($"th4 {Interlocked.Increment(ref increament)}");
27         Console.WriteLine($"th4 {increament++}");
28 });
29 
30 th1.Start();
31 th2.Start();
32 th3.Start();
33 th4.Start();
34 Console.ReadKey();
非原子并行计算

  • 模拟锁

用Exchange函数实现锁

 1         //0 for false, 1 for true.
 2         private static int usingResource = 0;
 3         //A simple method that denies reentrancy.
 4         static bool UseResource()
 5         {
 6             //0 indicates that the method is not in use.
 7             if (0 == Interlocked.Exchange(ref usingResource, 1))
 8             {
 9                 Console.WriteLine("{0} acquired the lock", Thread.CurrentThread.Name);
10 
11                 //Code to access a resource that is not thread safe would go here.
12 
13                 //Simulate some work
14                 Thread.Sleep(500);
15 
16                 Console.WriteLine("{0} exiting lock", Thread.CurrentThread.Name);
17 
18                 //Release the lock
19                 Interlocked.Exchange(ref usingResource, 0);
20                 return true;
21             }
22             else
23             {
24                 Console.WriteLine("   {0} was denied the lock", Thread.CurrentThread.Name);
25                 return false;
26             }
27         }
用Exchange模拟锁

用CompareExchange函数实现锁

 1         private double totalValue = 0.0;
 2 
 3         public double Total { get { return totalValue; } }
 4 
 5         public double AddToTotal(double addend)
 6         {
 7             double initialValue, computedValue;
 8             do
 9             {
10                 initialValue = totalValue;//---(1)
11                 computedValue = initialValue + addend;//---(2)
12 
13             }
14             while (initialValue != Interlocked.CompareExchange(ref totalValue,
15                 computedValue, initialValue));
16             //Interlocked.CompareExchange：比较totalValue与initialValue是否相同，如果相同，则用computedValue的值覆盖totalValue
17 
18             //如果totalValue与initialValue值不相同，则说明在（1）与（2）步骤执行的同时，
19             //其他线程执行了对totalValue进行了改变
20             return computedValue;
21         }
CompareExchange模拟锁

 

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

 

posted on 2018-05-06 14:23  DeeperMiner  阅读(252)  评论(0)  编辑  收藏  举报

导航