前提在运行多线程前提下.
因为在大多数计算机上，增加变量操作不是一个原子操作，需要执行下列步骤：
- 将实例变量中的值加载到寄存器中。
- 增加或减少该值。
- 在实例变量中存储该值。
如果不使用 Interlocked 类的 Increment 和 Decrement，线程会在执行完前两个步骤后被抢先。然后由另一个线程执行所有三个步骤。当第一个线程重新开始执行时，它改写实例变量中的值，造成第二个线程执行增减操作的结果丢失。
请见如下例子:
using System;
using System.Threading;
class Test
{
static void Main()
{
Thread thread1 = new Thread(new ThreadStart(ThreadMethod));
Thread thread2 = new Thread(new ThreadStart(ThreadMethod));
thread1.Start();
thread2.Start();
thread1.Join();
thread2.Join();
// Have the garbage collector run the finalizer for each
// instance of CountClass and wait for it to finish.
GC.Collect();
GC.WaitForPendingFinalizers();
Console.WriteLine("UnsafeInstanceCount: {0}" +
"\nSafeCountInstances: {1}",
CountClass.UnsafeInstanceCount.ToString(),
CountClass.SafeInstanceCount.ToString());
}
static void ThreadMethod()
{
CountClass cClass;
// Create 100,000 instances of CountClass.
for(int i = 0; i < 100000; i++)
{
cClass = new CountClass();
}
}
}
class CountClass
{
static int unsafeInstanceCount = 0;
static int safeInstanceCount = 0;
static public int UnsafeInstanceCount
{
get {return unsafeInstanceCount;}
}
static public int SafeInstanceCount
{
get {return safeInstanceCount;}
}
public CountClass()
{
unsafeInstanceCount++;
Interlocked.Increment(ref safeInstanceCount);
}
~CountClass()
{
unsafeInstanceCount--;
Interlocked.Decrement(ref safeInstanceCount);
}
}