What is the problem with DLLs and the Registry?

Question

Hi all,

I was watching the WWDC 2009 Keynote and something someone said about Windows 7/Vista got me curious..

The speaker claimed that 7 was still a poor operating system because it still used the same technologies such as DLLs and the registry. How accurate are his claims and how different is OS X doing it? Even os x has dynamically loaded libraries right? I guess the Registry thing might have some weight..

Can anyone explain to me the differences in each OS' strategy?

I'm not trying to incite fanboys here or anything, I just want to know how both operating systems tackle problems in general..

Thanks,

kreb

Answer 1

DLL's are bad variations of libaries since they are unable to operate on their own, to use them a further wrapper executable is called(automatically), which adds unrequired overhead and makes it much harder to tell which libraries are actually in use. Another less important flaw, is the inability for systems to truely share a library. *nix systems avoid this by having libraries exist on the top level running on their own or under a larger wrapper(like kde-init ), the libraries may be shared by any applications, meaning only a single copy of each library is required, and you may at any time kill a single library with ease as required.

The registry is a great idea, except for the fact that it is used for so much, almost anything you install will use the registry, and a corrupt registry and render your operating system almost completely useless until it's fixed. This is avoided in *nix systems by having multiple different files for different content, drivers are refered to via Xorg's config file, installed applications will be written to their own database, and keys or identification will often be written into a directory, rather than a single all purpose file. This reduces the likely hood of a serious failure and means that at any time you can probably still repair the system. If Xorg becomes corrupt you just reconfigure it, if the installed applications database becomes corrupt you can repair or rebuild it, and should an applications individual settings directory become corrupt you need only reinstall one application(and most good commercial aps should have a way to repair this anyway)

Answer 2

Of course both operating systems have facilities for using DLLs (they're called dylibs or Frameworks on OS X depending on how they're packaged).dylibs are very much like DLLs--they are a dynamically linked library and as such there may be multiple versions of them floating around. Frameworks, on the other hand, are really a directory structure. They contain dynamically linked libraries (potentially multiple versions of them), resources, headers, documentation, etc. The dynamic linker on OS X automatically handles choosing the correct library version from the framework for each executable. The system appears to work better than Windows' DLL management which is, well, quite a mess still (of course, Windows' system is tied by legacy issues that Apple dropped when they moved to OS X). To be fair, Unix has had a solution to this problem for a long time, as well using symbolic links to link dylibs to their correct versioned implementation, allowing multiple installed versions.

There is no OS X equivalent of the Windows registry. This is good and bad. The good side is that it's much harder to corrupt an entire OS X system with a registry screw up. OS X instead stores configuration in many separate files, usually one or more per application, user, whatever. These files are generally a plist (an XML schema representing dictionaries, arrays, and primitive types) formatted file. The bad side is that, by retaining this Unix-y heritage, OS X doesn't have the same über-admin tools that can churn through the registry and do all sorts of crazy things.

Answer 3

DLLs

The major difference between OS X and Windows is that Windows historically tried to save space/memory by having everyone share code (i.e. you install one DLL, everyone can use it). Apple statically compiles (well, not really, but it may as well be) all of the non-system libraries into every application. Wastes disk space/memory, but makes app deployment way easier and no versioning issues.

Registry

OS X does have a registry, they're just flat files called plists, instead of a magic component that's mostly like a filesystem except where it's not. Apple's approach makes it easy to migrate settings from one machine to another, whereas Windows' approach is faster in-memory, and allows apps to easily "watch" a key without taking a big perf hit (i.e. one app changes a key and the other instantly knows about it).

In conclusion

The keynote presenter's full of it, 10.6 is mostly the same code as 10.5, which was mostly the same code as 10.4 et al, just like Win7 is mostly Vista, which is mostly Server '03, etc. There's far too much tested code in an operating system to throw it away every release, especially if you actually want your customers' apps to work.