How to serialize/externalize Scheme procedures

[oliver.flasch@cs.uni-dortmund.de]

Hi,

I need to serialize procedures (and later closures) via XStream
(http://xstream.codehaus.org/) at the Kawa toplevel to save them to disk
and to transfer them over a network.

In order to get this to work, I modified gnu.bytecode.ArrayClassLoader
(from kawa-1.9.1.tar.gz, source code attached) to keep the compiled
bytecodes, which seems to work fine.

I then serialized the module class of a simple procedure "foo" to XML
(at the toplevel):

# (define (foo a) (+ a 42)) ; a simple procedure
# (define module-class (invoke foo:module 'getClass)) ; the procedure's
module class ("atEvalLevel")
# (define module-classloader (invoke module-class 'getClassLoader))
# (module-class:foo 3) ; => 45, works OK
# (export-to-xml (module-classloader:getBytecodeMap)
"/home/oflasch/bcm.xml") ; serialize the "bytecode map" of my modified
ArrayClassLoader

...and finally tried to de-serialize the module class again, which
failed quite miserably:

# (define acl
   (make <gnu.bytecode.ArrayClassLoader>
    ((<java.lang.Thread>:currentThread):getContextClassLoader)
    (import-from-xml "/home/oflasch/bcm.xml"))) ; make a new
ArrayClassLoader to load the de-serialized bytecodes

# (define imported-class (acl:loadClass (make <java.lang.String>
"atEvalLevel")))

# imported-class:foo ; => java.lang.Object
atEvalLevel.foo(java.lang.Object), OK, the "foo" method seems to be
there

# (make imported-class) ; throws an
java.lang.ExceptionInInitializerError
# (imported-class:foo 1) ; always throws an
java.lang.NoClassDefFoundError


The ExceptionInInitializerError gave me the following stack trace:

<StackTrace>
        java.lang.ExceptionInInitializerError
                (message:) java.lang.ExceptionInInitializerError
                (caused by...)
        java.lang.ExceptionInInitializerError
                (message:) null
                (caused by...)
        java.lang.NullPointerException
                (message:) null
        gnu.expr.Compilation.findForImmediateLiterals(Compilation.java:2826)
        gnu.expr.Compilation.setupLiterals(Compilation.java:2781)
        atEvalLevel.<clinit>(<string>)
        sun.reflect.NativeConstructorAccessorImpl.newInstance0(Native Method)

sun.reflect.NativeConstructorAccessorImpl.newInstance(NativeConstructorAccessorImpl.java:39)

sun.reflect.DelegatingConstructorAccessorImpl.newInstance(DelegatingConstructorAccessorImpl.java:27)
        java.lang.reflect.Constructor.newInstance(Constructor.java:494)
        gnu.expr.PrimProcedure.apply(PrimProcedure.java:238)
        gnu.mapping.CallContext.runUntilDone(CallContext.java:251)
        gnu.mapping.CallContext.runUntilValue(CallContext.java:315)
        gnu.kawa.reflect.Invoke.applyN(Invoke.java:199)
        gnu.kawa.reflect.Invoke.apply(Invoke.java:98)
        gnu.mapping.CallContext.runUntilDone(CallContext.java:251)
        gnu.expr.ModuleExp.evalModule(ModuleExp.java:296)
        kawa.lang.Eval.evalBody(Eval.java:99)
        kawa.lang.Eval.evalBody(Eval.java:42)
        kawa.standard.Scheme.eval(Scheme.java:847)
        kawa.standard.Scheme.eval(Scheme.java:830)
</StackTrace>

I must confess that I'm still not very comfortable with Kawa's
internals, although the Website and especially Per Bothner's "Kawa
internals" papers have been a great help. I would of cause be happy to
contribute my code, if I get the procedure serialization to work. :)
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