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下面的代码示例说明增加和减少整数值的线程安全方式。SafeInstanceCount 始终为 0。但是 UnsafeInstanceCount 不一定为 0,因为在增加和减少计数之间会出现争用条件。此效果在多处理器计算机上尤其明显。
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);
}
}