Comments on: Making JNI cross platform

By: Dmitri

Dmitri — Fri, 11 Jun 2010 23:55:19 +0000

Thanks for this - saved me a lot of poking around to find the different options. One to add: x86 is now reported as 'x86'.

By the way, that assert is a little misplaced - toLowerCase() can't return null.

By: zeeman

zeeman — Mon, 14 Jul 2008 19:31:26 +0000

Have a look at one-jar It supports a single jar for different os.arch/os.name with native libraries.

By: John Abraham

John Abraham — Tue, 01 Apr 2008 15:43:52 +0000

Hello there Sam. I notice you are using MTJ and JNI matrix operations. I fixed some bugs in MTJ, and see you have too. We need to move MTJ to a new server. Can you contact me? Thanks!

By: Sam

Sam — Sun, 20 May 2007 17:16:01 +0000

Paul, it's all matrix stuff... a Fortran library that sits atop of BLAS and LAPACK. We got a 20x speedup using the JNI! The matrix library MTJ has a JNI substitute for some of its internal calculations, but it actually has some serious bugs in its JNI code... I've been in contact with the author about a few other bugs, so I'll probably collate a big patch at some point and send it over.

I don't expect the JNI to work as fast on JVMs that do not support pinning (e.g. the IBM JVM) as it involves GB arrays being passed between Java and C... we explicitly check for that.

By: Sam

Sam — Sun, 20 May 2007 17:08:59 +0000

I probably exaggerated by saying it's a big disadvantage not to be able to ship native libs in the jar, but it is certainly an inconvenience. I prefer the idea of one file per version (for small to medium builds), rather than one file per version per OS per CPU, as that defeats the point of compile once run anywhere.

Incidentally, I would never encourage use of a JNI library as a complete replacement for a Java library... we always have a pure Java alternative sitting there for automatic use if the JNI version isn't available.

Even in our build system it is also easier to have a flat list of files... a directory structure would mean having to get all the developers to setup system variables for each JNI they may be running.

By: Paul Hammant

Paul Hammant — Sun, 20 May 2007 03:17:47 +0000

Out of interest, what was the mathematics operation you were speeding up by calling JNI ?

By: Casper Maxwell

Casper Maxwell — Sat, 19 May 2007 21:05:12 +0000

Nice post but why do you think "This has a big disadvantage as it doesn’t allow you to include native libraries in jar files."? I dont see any BIG disadvantage. If it is a big project, you should already have an installer which copies required jars and dlls to installation directory. And for small projects you can directly give specific jars + dlls for specific os+architecture.

But you are right that naming is a problem (although not a big one).