我试图衡量访问值类型和引用类型列表时使用afor和a的区别foreach。
我使用以下类进行分析。
public static class Benchmarker
{
public static void Profile(string description, int iterations, Action func)
{
Console.Write(description);
// Warm up
func();
Stopwatch watch = new Stopwatch();
// Clean up
GC.Collect();
GC.WaitForPendingFinalizers();
GC.Collect();
watch.Start();
for (int i = 0; i < iterations; i++)
{
func();
}
watch.Stop();
Console.WriteLine(" average time: {0} ms", watch.Elapsed.TotalMilliseconds / iterations);
}
}
我使用double我的值类型。我创建了这个“假类”来测试引用类型：
class DoubleWrapper
{
public double Value { get; set; }
public DoubleWrapper(double value)
{
Value = value;
}
}
最后，我运行了这段代码并比较了时差。
static void Main(string[] args)
{
int size = 1000000;
int iterationCount = 100;
var valueList = new List<double>(size);
for (int i = 0; i < size; i++)
valueList.Add(i);
var refList = new List<DoubleWrapper>(size);
for (int i = 0; i < size; i++)
refList.Add(new DoubleWrapper(i));
double dummy;
Benchmarker.Profile("valueList for: ", iterationCount, () =>
{
double result = 0;
for (int i = 0; i < valueList.Count; i++)
{
unchecked
{
var temp = valueList[i];
result *= temp;
result += temp;
result /= temp;
result -= temp;
}
}
dummy = result;
});
Benchmarker.Profile("valueList foreach: ", iterationCount, () =>
{
double result = 0;
foreach (var v in valueList)
{
var temp = v;
result *= temp;
result += temp;
result /= temp;
result -= temp;
}
dummy = result;
});
Benchmarker.Profile("refList for: ", iterationCount, () =>
{
double result = 0;
for (int i = 0; i < refList.Count; i++)
{
unchecked
{
var temp = refList[i].Value;
result *= temp;
result += temp;
result /= temp;
result -= temp;
}
}
dummy = result;
});
Benchmarker.Profile("refList foreach: ", iterationCount, () =>
{
double result = 0;
foreach (var v in refList)
{
unchecked
{
var temp = v.Value;
result *= temp;
result += temp;
result /= temp;
result -= temp;
}
}
dummy = result;
});
SafeExit();
}
我选择Release和Any CPU选项，运行程序，并得到了以下时间：
valueList for: average time: 483,967938 ms
valueList foreach: average time: 477,873079 ms
refList for: average time: 490,524197 ms
refList foreach: average time: 485,659557 ms
Done!
然后，我选择了Release和x64选项，运行了程序并得到了以下时间：
valueList for: average time: 16,720209 ms
valueList foreach: average time: 15,953483 ms
refList for: average time: 19,381077 ms
refList foreach: average time: 18,636781 ms
Done!
为什么x64位版本这么快？我期望有所不同，但不会那么大。
我无权访问其他计算机。您能在您的机器上运行此程序并告诉我结果吗？我正在使用Visual Studio 2015，并且具有Intel Core i7 930。
这是SafeExit()方法，因此您可以自己编译/运行：
private static void SafeExit()
{
Console.WriteLine("Done!");
Console.ReadLine();
System.Environment.Exit(1);
}
根据要求，使用double?代替我的DoubleWrapper：
任何CPU
valueList for: average time: 482,98116 ms
valueList foreach: average time: 478,837701 ms
refList for: average time: 491,075915 ms
refList foreach: average time: 483,206072 ms
Done!
x64
valueList for: average time: 16,393947 ms
valueList foreach: average time: 15,87007 ms
refList for: average time: 18,267736 ms
refList foreach: average time: 16,496038 ms
Done!
最后但并非最不重要的一点：创建x86配置文件可为我提供与使用几乎相同的结果Any CPU。
