DLL Hell : Java Glossary

by Roedy Green ©1996-2009 Canadian Mind Products
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DLL Hell

Dynamic Link Library. This is the stupidest idea every foisted on the computing public. You can thank Microsoft for this lunacy and for the second stupidest idea, the registry. It started out well intentioned. If two different programs are using the same code, should they not share a common copy? DLLs also tend to stay loaded even after they are no longer necessary. Often this saves the effort of reloading them if they are used again soon. This is a Good Thing ™ What went wrong?

The main error was giving DLLs only 8+3 names. If two different companies called their DLL PLOTTER.DLL they are assumed to be the same DLL. Either company can sometimes accidentally use the other company’s DLL. It all depends on which version of the DLL was loaded first.
The second error was Microsoft putting out into the world dozens of different versions of the same DLL all with the same name. In theory all programs should use the latest version. However, there is nothing to stop an old version from being loaded instead. Further, some program will only work with the old version and some only with the new. Every time you install a new program it may install some DLLs that stop your existing programs from working.
Instead of managing the DLLs in a carefully controlled way as part of the operating system, application programs are responsible for installing them. Cowboy coding that ignores the conventions makes a horrible problem even worse.
A DLLs muddles together in its address space the data for all its clients. They are not kept separate by hardware. It is totally up to the DLL to keep it all straight.
You can’t change DLLs to a new version without rebooting, not even the disk copy, let alone the RAM image. Java can change code on the fly without so much as stopping the program. Surely Microsoft could work out a method to change a DLL that did not require such drastic measures. Some Unix machines run for years without rebooting. To replace a DLL with a new one, you must use the inuse utility to allow you to replace the DLL and then reboot to clear the in-RAM copy.
```
inuse test.dll C:\winnt\system32\test.dll /y
```
Alternatively, you can reboot, and then replace the DLL, so long at it is not loaded.
Microsoft closed its eyes to these problems for a decade. Instead it concentrated on adding dancing paper clips to its applications. They have finally decided to at least tackle the problem in a half-hearted, half-assed, kludge-o-matic way. The whole concept of DLL needs a total overhaul. They refuse to bite the bullet and totally rethink this abortion.

If you want to access code in a DLL from Java, you will need to write some JNI glue.

JNI
unlocker

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