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Revision as of 09:26, 26 June 2002 by Uriyan (talk | contribs) (Corrected some things)(diff) ← Previous revision | Latest revision (diff) | Newer revision → (diff)DLL-hell is a describing term for troublesome situations caused by unnecessary copies of Dynamic Link Libraries (DLLs) installed on a particular copy of an operating system, and conflicts between various versions of these libraries.
Generally, the concept of DLLs means that many applications can share the same DLL file; however, in many cases, applications may introduce a changed version of a particular DLL which is already present on a system, either overwriting the old copy (which can, in turn, break compatibility with other applications), or install another copy, wasting disk space, memory space and slowing program load times because it takes more time to locate the right DLL among many.
As time goes by, the DLL-hell problem can become only worse, since software that installed the unnecessary DLLs is unlikely to remove them when uninstalled. This could eventually cause a chaos of thousands of mysterious DLL-files, some of which are necessary for the system to function normally, while others are just wasting space, and with no way to distinguish between them.
DLL-hell is a very common phenomenon on Microsoft Windows systems, as they lack sophisticated facilities for system file management (and existing programs often disrespect the few facilities that do exist). However, virtually all operating systems that have a sufficient amount of DLL-using software installed on them can be brought into the DLL-hell state; thus, the GNOME desktop environment running under Linux is notorious for the enormous number of DLL extensions it uses.
There are several measures known to avoid DLL-hell, which have to be used together:
- Ship the operating system with a capable package manager (such as RPM for RedHat systems), that would be able to track the DLL dependencies. Declare using the package manager good style and using manual installs bad style.
- Have a central authority for distributing the library. Changes to the library can be proposed to this authority; it can also make sure compatibility is preserved in the developed branches. If older software is incompatible with the current library, the authority can provide a compatibility interface for it, or bundle the old version under as a distinct package.
- If software developers are in need of customizing a library, if the main library release is unlikely to incorporate the things that they need, they can use static linking against their own version, or create a new package (with a different name) for it.
- Proper software design is paramount. DLLs are best for modularizing the system's components and as third-party libraries; their usage is not imperative in all cases. For example, if there's an application that needs a library that won't be used anywhere else, they can be linked statically, with no space penalty and with a speed gain. Also, some platforms support pipes between programs, a less sophisticated but more efficient interface than DLL calls.