C# - Default library has better performance?

Question

Hello,

Earlier today i made myself a lightweight memory stream, which basically writes to a byte array. I thought i'd benchmark the two of them to see if there's any difference - And there was:

(writing 1 byte to the array) MemoryStream: 1.0001ms mine: 3.0004ms

Everyone tells me that MemoryStream basically provides a byte array and a bunch of methods to work with it.

My question: Does the default C# library have a slightly better performance than the code we write? (maybe it runs in release rather than debug?)

Answer 1

Id wager that Microsoft's implementation is a wee bit better than yours. ;)

Did you check the source?

Answer 2

The folks at Microsoft are much smarter than you and I and most likely have written a better optimized wrapper over Byte[], much better than something that you or I would implement.

If you are curious, I would suggest that you disassemble the types that you have recreated to see how exactly Microsoft has implemented them. In some of the more important areas of the framework (such as this I would imagine) you will find that the BCL calls out to unmanaged code to accomplish its goals.

Unmanaged code has a much better chance of outperforming managed code in cases like this since you can freely work with arrays without the overhead of a managed runtime (for things like bounds checking and such).

Answer 3

The .NET implementation was probably a bit better than your own, but also, how did you benchmark? A couple of million iterations, or just a few? Remember that you need to use a large test base so that you can eliminate some data (CPU being called away for a moment, etc) that will give false results.

Answer 4

Many of the framework assemblies are NGENed, which may give them a small boost by bypassing the initial JIT time. This is unlikely to be the cause of a 2ms difference, especially if you'd already warmed up your methods before starting the stopwatch, but I mention it for completeness.

Also, yes, the framework assemblies are built in "release" mode (optimisations on and checks off), not "debug."

Answer 5

You probably used Array.Copy() instead of the faster Buffer.BlockCopy(). The fastest way is to use unsafe code with pointers. Check out how they do this in the Mono project (search for memcpy).