Creating objects - Perf implications

Here are a few examples of how we can create objects, and the perf implications of each way. In all those tests, I have used the following class as my benchmark.

public class Created

{

    public int Num;

    public string Name;

    public Created(int num, string name)

    {

        this.Num = num;

        this.Name = name;

    }

}

We have a value type and a reference type that are passed to the constructor.

The test code is here:

static void Main(string[] args)

{

    int iterations = 1000000;

    Stopwatch watch = Stopwatch.StartNew();

    for (int i = 0; i < iterations; i++)

    {

        CreateInstance(i);

    }

    Console.WriteLine(watch.Elapsed);

}

Here it my base line, calling the constructor directly.

private static Created CreateInstance(int i)

{

    return new Created(i, i.ToString());

}

This executes in 00.3648117 seconds on severely underpower laptop. Pretty good, considering we just created a million instances. Now, let us see what happens if we user Activator, shall we?

private static Created CreateInstance(int i)

{

    return (Created)Activator.CreateInstance(

                        typeof(Created), i, i.ToString());

}

This run depressingly slow, 06.8242636 seconds.

Let us try to improve that a bit, using GetUninitializedObject and directly invoking the constructor.

static ConstructorInfo ctor = typeof(Created).GetConstructors()[0];

private static Created CreateInstance(int i)

{

    object o = FormatterServices.GetUninitializedObject(typeof(Created));

    return (Created)ctor.Invoke(o, new object[]{i, i.ToString()});

}

This runs in 03.2422335 seconds, a significant improvement, but we can do even more, I think.

We start by making the required definitions:

static ConstructorInfo ctor = typeof(Created).GetConstructors()[0];

delegate Created CreateCtor(int i, string s);

static CreateCtor createdCtorDelegate;

Then we generate a dynamic method to create the object, and turn that into a delegate:

DynamicMethod method = new DynamicMethod("CreateIntance", typeof(Created),

    new Type[] { typeof(int), typeof(string) });

ILGenerator gen = method.GetILGenerator();

gen.Emit(OpCodes.Ldarg_0);// i

gen.Emit(OpCodes.Ldarg_1);// s

gen.Emit(OpCodes.Newobj, ctor);// new Created

gen.Emit(OpCodes.Ret);

createdCtorDelegate = (CreateCtor)method.CreateDelegate(typeof(CreateCtor));

Now, in the method itself, all we have to do is call this delegate:

private static Created CreateInstance(int i)

{

    return createdCtorDelegate(i, i.ToString());

}

And now that run very fast... 00.4314517 seconds. Almost as fast as our baseline. But this is not really a good example, I am afraid. At least, not a god example of generally creating instances, let us make this into the more general form, shall we?

We will change the CreateCtor delegate to the following signature:

delegate object CreateCtor(object[] args);

And the generation of the dynamic method to use the generic approach:

DynamicMethod method = new DynamicMethod("CreateIntance", typeof(Created),

    new Type[] { typeof(object[]) });

ILGenerator gen = method.GetILGenerator();

gen.Emit(OpCodes.Ldarg_0);//arr

gen.Emit(OpCodes.Ldc_I4_0);

gen.Emit(OpCodes.Ldelem_Ref);

gen.Emit(OpCodes.Unbox_Any, typeof(int));

gen.Emit(OpCodes.Ldarg_0);//arr

gen.Emit(OpCodes.Ldc_I4_1);

gen.Emit(OpCodes.Ldelem_Ref);

gen.Emit(OpCodes.Castclass, typeof(string));

gen.Emit(OpCodes.Newobj, ctor);// new Created

gen.Emit(OpCodes.Ret);

createdCtorDelegate = (CreateCtor)method.CreateDelegate(typeof(CreateCtor));

We need to make the following modification to our CreateInstance method:

private static Created CreateInstance(int i)

{

    return (Created)createdCtorDelegate(new object[]{i, i.ToString()});

}

And now it runs in.... 00.5018288.

Now, what does this long and arcane post tells us?

Creating instances, no matter how many, is really cheap. Remember that I had to do a million iteration to get something measurable.

The table bellow give the final statistics. Pay attention to the last column, this gives the amount of time it take to create a single instance. Even the most hard core perf fanatic would be hard pressed to argue over 0.000007 seconds. At least I hope so :-)

And just to clarify, you are not going to see anything like creating a million object in most scenarios that you care about. In other words, you can probably leave things well enough alone.

Print | posted on Wednesday, February 27, 2008 5:10 PM