Frege/frege-interpreter

Add OSGi support

renatoathaydes opened this issue · 10 comments

renatoathaydes commented

Hi,

I have noticed that even though frege-core is OSGi-ready, the frege-interpreter isn't.

Do you have plans to add OSGi support?

I've tried to wrap the interpreter into a bundle but unfortunately it seems the way Frege loads classes doesn't work inside OSGi.

Errors I get:

frege.runtime.Undefined: [E <console>.fr:1: Could not import module frege.Prelude
    (java.lang.ClassNotFoundException: frege.Prelude), E <console>.fr:1: Could not import module frege.prelude.PreludeBase
    (java.lang.ClassNotFoundException: frege.prelude.PreludeBase), E <console>.fr:1: Could not import module frege.prelude.PreludeList
    (java.lang.ClassNotFoundException: frege.prelude.PreludeList), E <console>.fr:1: Could not import module frege.prelude.PreludeText
    (java.lang.ClassNotFoundException: frege.prelude.PreludeText), E <console>.fr:1: Could not import module frege.prelude.PreludeMonad
    (java.lang.ClassNotFoundException: frege.prelude.PreludeMonad), E <console>.fr:1: Could not import module frege.prelude.PreludeIO
    (java.lang.ClassNotFoundException: frege.prelude.PreludeIO), E <console>.fr:1: Could not import module frege.prelude.PreludeArrays
    (java.lang.ClassNotFoundException: frege.prelude.PreludeArrays), E <console>.fr:1: Could not import module frege.java.util.Regex
    (java.lang.ClassNotFoundException: frege.java.util.Regex)]

If you can give any ideas on how this may work or you will add support for OSGi soon, I would appreciate.

Ingo60 commented

FYI, the compiler uses ClassLoader.loadClass and Class.getAnnotation to load information from class files.

I'm really not sure why OSGi would not allow this, and I hope @talios will comment on it.

BTW, the eclipse-plugin is also a bundle (or is it?), and the same (compiler) code is working just fine there.

renatoathaydes commented

If it were possible to set the ClassLoader to use to load classes, I believe this problem could be avoided.

Ingo60 commented

This is not possible, nor should it be needed (I think).
The compiler creates a class loader for the purpose of module imports:

ClassLoader.current >>= URLClassLoader.new urlarr

which should be more or less equivalent to Java

 new URLClassLoader(urlarr, frege.runtime.Meta.FregePackage.class.getClassLoader())

where urlarr is an array of URLs built from

  1. the current class path (unless -nocp option is given)
  2. the value of the option -fp (i.e frege path)

The rather complicated way to crete the class loader (and to create a separate class loader at all) results from difficulties in eclipse to get away with the default class loader, as far as I remember. In any case, it is so that the eclipse plugin (which uses the same code as the batch compiler and the REPL) is able to load different library modules than the one it is running itself. (Isn't that what OSGi is all abut?)

So I guess all you need is a way to tell the REPL where the standard library it is suposed to use is located?

Ingo60 commented

I actuall erred rgd. forName, actually we use ClassLoader.loadClass

renatoathaydes commented

In OSGi, each bundle (roughly a jar) has its own classloader, and can see only the classes it imports from other bundles. There's no single classpath, as in regular Java applications.

Is it possible to pass the -fp option programmatically, as obviously I am using frege-interpreter as just a dependency of my application, not running it from the command line.

Ingo60 commented

I'm not sure if system property java.class.path can be altered.
If it is, this would be morally equivalent to invoke the compiler with a certain class path, and would result in a class loader that uses that path. Just make sure to use the correct path.separator

renatoathaydes commented

The interpreter is fundamentally at odds with how OSGi works. I added support for "system libs" in my Gradle plugin osgi-run so that I can run code like this, that wants to load its own classes, from OSGi.

Here's how it works (if anyone in the future is interested in this: renatoathaydes/osgi-run@9563d80)

talios commented

I was meaning to respond to this the other day, the latest Frege.jar that I'm publishing to Maven Central now no-longer has OSGi exports added ( I was originally repacking the entire jar, but now that I'm publishing both the jdk7 and jdk8 flavours that was getting a bit awkward. ).

Ideally we should get the @Ingo60's release process ( the MakeFile? ) to add he MANIFEST.MF entries when creating the jar file.

renatoathaydes commented

@talios Just adding the manifest entries is not enough to get the Frege interpreter to run in OSGi. Specifically, the way you load classes at runtime (which I don't know if only the interpreter does, or core also does) cannot work in OSGi unless you let users provide a classloader.