Till now I normally used the cacls command on the commandline for modifying ntfs file permissions. I always used the /E /T /G switches but soon found out that this does a recursive change on all folders/files and doesn't use the inheritance flag. Normally not really a big problem but updating the security descriptors on a large directory tree takes time. Too much time if you ask me and so my search for a better alternative was started. I quickly found references to xcacls.vbs / xcacle.exe . These seem to fix inheritance related issues that cacls cannot do.
But I found a tool that is much easier to use these and that is fileacl.exe. When adding permissions to a folder then underlying files and folder will inherit these by default which is what you normally would want to. The syntax is also somewhat better and also provides some advanced enhancements.
I was yet again busy with a generic data layer. I like type safety as it provides compile time safety instead of run-time. The current released Db4o build (6.1) does not support type safe result list thus I had a need to convert these. My first approach was to just do a foreach like the following example:
public static System.Collections.Generic.IList<T> Convert1<T>(
System.Collections.Generic.IList<T> result = new System.Collections.Generic.List<T>(source.Count);
foreach (T o in source)
But after I had this working I thought that this could be slow and that another solution was probably faster. I did a quick google search and ended up at a post of Bil Simser. There I saw some approaches in the comments but without additional information about its performance. So I made a little performance test where I tested not only the first example but also two others:
public static System.Collections.Generic.IList<T> Convert2<T>(
System.Collections.ArrayList list = new System.Collections.ArrayList(source);
return new List<T>(list.ToArray(typeof(T)) as T);
public static System.Collections.Generic.IList<T> Convert3<T>(
T output = new T[source.Count];
After creating an ArrayList I initialized it with 20.000.000 instances of my test class and then converted it to a type-safe IList<T>. After running it several times with no load on my system I got the following results:
Conversion one : ~2175ms
Conversion two : ~ 884ms
Conversion three : ~133ms
So my "vingerspitsgevoel" was right again! What amazes me is that the conversions timings are so far apart. At first I didn't think that the second conversion would differ that much compared with the first but I think the .ToArray(..) method has CLR optimizations just as .CopyTo(..) method in the third example. The third conversion is more then 16 times faster then the first and even more then 6,5 times faster then the second.
The third conversion is even faster with much smaller arrays and lists (200.000 items). Then it is ~26 times faster then the first and ~7 times faster then the second conversion. I did this test on a Intel 3GHz D processor with 2GB of RAM on Windows XP Pro with the .net 2.0 framework.
So if you were searching for (probably the fastest) ArrayList / IList to IList<T> conversion then you have found it. I immediately added the third conversion method to my personal framework code and I suggest that you do to after seeing these results.