I’ve written small test program and was surprised why lock {} solution performs faster than lock-free but with [ThreadStatic] attribute over static variable.
[ThreadStatic] snippet:
[ThreadStatic]
private static long ms_Acc;
public static void RunTest()
{
Stopwatch stopwatch = new Stopwatch();
stopwatch.Start();
int one = 1;
for (int i = 0; i < 100 * 1000 * 1000; ++i) {
ms_Acc += one;
ms_Acc /= one;
}
stopwatch.Stop();
Console.WriteLine("Time taken: {0}", stopwatch.Elapsed.TotalSeconds);
}
lock {} snippet:
private static long ms_Acc;
private static object ms_Lock = new object();
public static void RunTest()
{
Stopwatch stopwatch = new Stopwatch();
stopwatch.Start();
int one = 1;
for (int i = 0; i < 100 * 1000 * 1000; ++i) {
lock (ms_Lock) {
ms_Acc += one;
ms_Acc /= one;
}
}
stopwatch.Stop();
Console.WriteLine("Time taken: {0}", stopwatch.Elapsed.TotalSeconds);
}
On my machine first snippet takes 4.2 seconds; second – 3.2 seconds, which is 1 second faster. Without ThreadStatic and lock – 1.2 seconds.
I’m curious why [ThreadStatic] attribute in this simple example adds so many to program execution time?
UPDATE: I feel very sorry, but these results are for DEBUG build. For RELEASE one I got completely different numbers: (1.2; 2.4; 1.2). For DEBUG numbers were (4.2; 3.2; 1.2).
So, for RELEASE build there seems to be no [ThreadStatic] performance penalty.
For RELEASE build there seems to be almost no [ThreadStatic] performance penalty (only slight penalty on modern CPUs).
Here comes dis-assembly code for
ms_Acc += one; forRELEASEoptimization is enabled:No
[ThreadStatic],DEBUG:No
[ThreadStatic],RELEASE:[ThreadStatic],DEBUG:[ThreadStatic],RELEASE: