RPGDX > Forums > Design and programming > On better engine design practice.

DeveloperX · Posted: Mon Mar 02, 2009 3:01 am Post subject: On better engine design practice.

This is more of a question to the more experienced developers that may be lingering around.

I make heavy use of the STL in my code.

I've been using the singleton pattern in my games; and as a result, I end up with code that functions fine on linux, and does not when it is built on windows.

Apparently there is a major flaw in the logic of the STL, and using singletons in the same code just causes major headaches.

Singletons, as you likely already know, are statically declared instances of a class....and if you have any STL code in them then it simply will segfault under windows.

Rainer Deyke · Demon Hunter Joined: 05 Jun 2002 Posts: 672

I try to avoid singletons in my code. If it doesn't absolutely have to be global, I use a normal (non-singleton) object, even if the object is the only one of its class. In the rare cases where I actually want something to be global, I tend to use a regular global or static variable, without the singleton machinery.

That said, the problem with your code is probably the use of 'const char *' as a key. Use 'std::string'. (Also, if the 'Foo*' is a pointer to a dynamically allocated object, it should probably be 'boost::shared_ptr<Foo>' or another smart pointer class instead.)

DeveloperX

Rainer Deyke · Demon Hunter Joined: 05 Jun 2002 Posts: 672

I see. I don't suppose you have a minimal complete example program that demonstrates the problem?

Actually it wouldn't surprise if MinGW was seriously bugged, seeing as it's a Windows port of an old, old version of gcc. Visual C++ 2005 has much better C++ language support.

Simple workaround:

Hajo

DeveloperX · Posted: Mon Mar 02, 2009 9:17 am Post subject:

Rainer: THANK YOU! You helped me greatly!

(if it weren't for that post above, I'd still be fighting segfaults trying to build a damned windows release of my jam-entry!)
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Tenshi · Posted: Mon Mar 02, 2009 4:52 pm Post subject:

I know you already solved the problem, but I think this is relatively similar. I am coding from Windows with "cross-platform" in mind and use MingGW to compile. But when I do static pointers I do the following:

Mattias Gustavsson · Posted: Tue Mar 03, 2009 2:01 pm Post subject:

About using strings for keys...

I'm a bit careful about using strings of any sort (especially std::string) as keys, ever since the time I was hired to optimize a game&engine which turned out to be using hundreds of megabytes for strings (lots of duplicates) and where string comparisons,copying and allocation was right at the top of the profiling results :P

So personally I use something I call a StringId, which basically is just a pointer to a string in a global table (a hashtable for faster lookup). That way, string comparisons is just a pointer compare and duplicating a StringId is just duplicating a pointer. Creating a new StringId instance is slower (involves looking up the string in the hash table, or insert it if it doesn't exist already), but that's ok as I tend to do that mostly during initialization.

Details:
http://www.colossusentertainment.com/pixiedocs/_string_id_8h-source.html
http://www.colossusentertainment.com/pixiedocs/_string_id_8cpp-source.html
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Hajo · Posted: Tue Mar 03, 2009 3:49 pm Post subject:

The people who designed Java knew that, too, and made all string literals internalized, and gave the String class the intern() function that does just this trick ;)

http://java.sun.com/j2se/1.4.2/docs/api/java/lang/String.html#intern()

Might be even more evidence how right Matthias is there.

Edit: The quotes belong to the url, but the forum software does not like them inside the url tags, and neither very much outside :(

DeveloperX · Posted: Tue Mar 03, 2009 4:02 pm Post subject:

Mattias Gustavsson · Posted: Tue Mar 03, 2009 4:34 pm Post subject:

Well, my StringId class is a bit more complicated than needed, as it also functions as a HashTableKey.

But my point was more conceptual: it's better to use shared strings, for both performance and memory. The way I see it, is that it doesn't hurt to worry about the small things, because you never know when they'll come back and bite you. Like a game requiring 4 times as much memory as a normal PC has, and therefore using the swapfile like crazy :D
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RedSlash · Mage Joined: 12 May 2005 Posts: 331

I know that GCC's STL uses copy-on-write optimizations on string, so in theory as long as you're taking advantage of this optimization (using consts properly, etc..), you should be reducing the effects of duplicate copies and comparisons. But I don't really know if it makes the difference, since I usually use const char *, and it seems to be consistant in behaviour.

Tenshi · Posted: Wed Mar 04, 2009 12:05 am Post subject:

I know in my case theoretically it shouldn't be using much memory at all because there will be few strings in memory in the first place and the majority of the time the strings aren't even actually directly referenced (iterators used). The only time the strings are even checked is if a script I write needs to directly address one, and I went with Strings because it's much easier than trying to keep track of integers when writing a billion scripts anyway.
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