Comments on: Don’t Call GC.Collect Every Frame

By: Colin

Colin — Thu, 10 Dec 2009 18:41:26 +0000

However, the concatenation of the three strings does create three new strings as the string objects are changed:
string tempString = "Hello";
tempString += " ";// tempString is now "Hello "
tempString += "World";//tempString is now "Hello World"
tempString += "!";//tempString is now "Hello World!"

So in total, 7 strings exist, but 4 of those were string literals, so only three ones were created new.

By: IGoByChad

IGoByChad — Wed, 09 Dec 2009 22:20:14 +0000

Well, .Net does not keep a list of every possible constant string around. That would truly be the rubbish. However, I'm not quite sure what you mean. By typing "Hello" we have created a fully qualified instance of the "Hello" string. You can do "Hello".Length if you wanted. It's very awkward looking at first. (You can do 1.ToString() as well!) However, it's a string nonetheless. When you assign it to the tempString, it does not create an entirely new copy of "Hello", but you created a string.

By: Name

Name — Wed, 09 Dec 2009 20:03:41 +0000

You might be interested to see this explanation: http://www.reddit.com/r/programming/comments/acue...

By: Bob

Bob — Wed, 09 Dec 2009 19:21:30 +0000

In the string example, aren't you only creating three strings? "Hello" is a constant (like " ") and setting tempString to it will just alter what it refers to. Or is .NET so rubbish that a string gets copied when it's assigned to a variable?

By: IGoByChad

IGoByChad — Wed, 09 Dec 2009 17:31:40 +0000

Yes! I saw the first article and coming from a C++ side, it was a very thorough review for me. The only reason I didn't link to that in the main article is that I wanted to keep the article focused.

Very good first article though, and I'm more than happy to have the further information in the comments. I recommend it for anyone who doesn't have a firm grasp on stack versus heap or even just the memory management of .Net.

By: BittermanAndy

BittermanAndy — Wed, 09 Dec 2009 17:20:49 +0000

Hi – author of Pandemonium (your second link) here. Top work on digging deeper and deeper! I'm always uncomfortable with simply accepting the received wisdom as well.

I'd just like to add that you linked to part two of my GC thoughts… at the risk of shamelessly plugging my own articles, part one talks about everything that happens during a garbage collection. It doesn't add any more information to your final conclusion (don't call GC.Collect every frame because the overhead is too high), but it may give some insight into why the overhead gets too high – in fact, what exactly the overhead consists of. Link: http://bittermanandy.wordpress.com/2008/10/19/gar...

Thanks!