据我所知,32位机器上的.NET内存模型保证32位字的写入和读取是原子操作,但不是在64位字上提供此保证。我已经编写了一个快速工具来在Windows XP 32位操作系统上演示这种效果,并获得与该内存模型描述一致的结果。.NET 3.5SP1 64位内存模型与32位内存模型
但是,我采用了这个相同的工具的可执行文件,并在Windows 7 Enterprise 64位操作系统上运行它,结果却截然不同。这两台机器都是相同的规格,只是安装了不同的操作系统。我预计.NET内存模型可以保证在64位操作系统上写入和读取32位和64位字都是原子的。我发现结果完全违背了这两个假设。在这个操作系统上,32位的读写操作没有被证明是原子的。
有人可以向我解释为什么这在64位操作系统上失败吗?
工具代码:
using System;
using System.Threading;
namespace ConsoleApplication1
{
class Program
{
static void Main(string[] args)
{
var th = new Thread(new ThreadStart(RunThread));
var th2 = new Thread(new ThreadStart(RunThread));
int lastRecordedInt = 0;
long lastRecordedLong = 0L;
th.Start();
th2.Start();
while (!done)
{
int newIntValue = intValue;
long newLongValue = longValue;
if (lastRecordedInt > newIntValue) Console.WriteLine("BING(int)! {0} > {1}, {2}", lastRecordedInt, newIntValue, (lastRecordedInt - newIntValue));
if (lastRecordedLong > newLongValue) Console.WriteLine("BING(long)! {0} > {1}, {2}", lastRecordedLong, newLongValue, (lastRecordedLong - newLongValue));
lastRecordedInt = newIntValue;
lastRecordedLong = newLongValue;
}
th.Join();
th2.Join();
Console.WriteLine("{0} =? {2}, {1} =? {3}", intValue, longValue, Int32.MaxValue/2, (long)Int32.MaxValue + (Int32.MaxValue/2));
}
private static long longValue = Int32.MaxValue;
private static int intValue;
private static bool done = false;
static void RunThread()
{
for (int i = 0; i < Int32.MaxValue/4; ++i)
{
++longValue;
++intValue;
}
done = true;
}
}
}
结果在Windows XP 32位:
Windows XP 32-bit
Intel Core2 Duo P8700 @ 2.53GHz
BING(long)! 2161093208 > 2161092246, 962
BING(long)! 2162448397 > 2161273312, 1175085
BING(long)! 2270110050 > 2270109040, 1010
BING(long)! 2270115061 > 2270110059, 5002
BING(long)! 2558052223 > 2557528157, 524066
BING(long)! 2571660540 > 2571659563, 977
BING(long)! 2646433569 > 2646432557, 1012
BING(long)! 2660841714 > 2660840732, 982
BING(long)! 2661795522 > 2660841715, 953807
BING(long)! 2712855281 > 2712854239, 1042
BING(long)! 2737627472 > 2735210929, 2416543
1025780885 =? 1073741823, 3168207035 =? 3221225470
通知BING(INT)如何不会被写入,并证明了32位读/写操作上原子这个32位操作系统。
结果在Windows 7企业版64位:
Windows 7 Enterprise 64-bit
Intel Core2 Duo P8700 @ 2.53GHz
BING(long)! 2208482159 > 2208121217, 360942
BING(int)! 280292777 > 279704627, 588150
BING(int)! 308158865 > 308131694, 27171
BING(long)! 2549116628 > 2548884894, 231734
BING(int)! 534815527 > 534708027, 107500
BING(int)! 545113548 > 544270063, 843485
BING(long)! 2710030799 > 2709941968, 88831
BING(int)! 668662394 > 667539649, 1122745
1006355562 =? 1073741823, 3154727581 =? 3221225470
注意,BING(长)和Bing(INT)都显示出来!为什么32位操作失败,更不用说64位操作了?
是否有可能编辑您的问题以使用工具栏上的“代码示例”格式?这是难以置信的难以阅读.. – JBRWilkinson 2010-06-07 16:57:04
我已经格式正确,但与TAB字符最初,而不是空间和预览看起来不错。当我发现发布完全失败时,我感到震惊。我现在修好了。 – 2010-06-07 16:58:59
我已经修好了:D – Femaref 2010-06-07 16:59:38