Edit: As a result of these tests, I’ve written a better-performing set of extension methods.
I recently wrote an extension method which uses an Expression Tree to create a Func which creates an instance of an object from its Type. With that done I thought I’d check the performance difference between my method and Activator.CreateInstance(), which it was intended to replace.
I wrote a simple console application which tested using new, Type.GetInstance() and Activator.CreateInstance() by creating 100,000 instances of objects with zero to three constructor parameters and calculating the average time of each construction. For Type.GetInstance() and Activator.CreateInstance() I created a single instance of each object before running the test so they could perform any caching outside of the actual performance measurement.
The results were as follows; the third column shows the total number of ticks taken to create 100,000 objects, the fourth the number of ticks taken per object:
A few things to note:
- Unsurprisingly, using new is always and by far the fastest way to go.
- With a parameterless constructor, using Activator.CreateInstance() is almost as fast as using new, and much, much faster than using Type.GetInstance().
- When your constructor takes one or more parameters, Type.GetInstance() takes about 70% the time of Activator.CreateInstance().
I find myself wondering why Type.GetInstance() isn’t faster than it is; after all, aren’t Funcs created by Expression Trees supposed to nearly as fastas regular code? I’ve not looked into it in any great detail, but I think its performance is weighed down by the generic nature of the method and the way the Funcs are cached.
Because the Funcs are cached in a dictionary which returns a Func<object, object, object, object>, calling the Func requires an Expression to cast each argument to its correct Type, and this introduces overhead. This is confirmed by looking at the Expression Visualiser in Visual Studio, which displays the created Lambda like this:
With these results, I’m going to update the parameterless overload of Type.GetInstance() to delegate to Activator.CreateInstance(), and I wonder if I might be able to use a generic helper class to cache a strongly-typed Func and so avoid the casting… something to consider (I’ve now considered it and written new methods). I guess it’s always best to make decisions based on data 🙂
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Print | posted @ Saturday, February 11, 2012 11:08 AM