Re: JNI incorrect conversion of C long to Java long (aka Re: SableVM on ARM fails to run HelloWorld)

On Tuesday 29 November 2005 18:44, Chris Develder wrote:
> The root cause of getting sablevm-1.12 working on our ARM device seems
> to be that a long value in C is not converted correctly to a Java long
> (via a JNI jlong, ie. a C long long).
>
> I verified that Java_java_io_VMFile_length
> (sablevm-classpath-1.12/native/jni/java-io/java_io_VMFile.c) correctly
> reads the file length as a long (794 for my HelloWorld.class). But
> conversion to jlong (defined in jni_md.h as long long) seems to go
> wrong: when inspecting the value in File.length()
> (sablevm-classpath-1.12java/io/File.java), it turns out to be 0.
>
> Thus, something seems to go wrong when passing the long long from C to a
> Java long through JNI... Any suggestions?

I have experienced the same bug (http://sablevm.org/bugs/158), and since jlong 
values are used in such common places as System.currentTimeMillis() (which is 
called from almost everywhere), things like "new Date()" return funny values.

It seems odd, but jlongArray data types are correctly passed to Java . You may 
rewrite the affected functions to return jlongArray values instead of jlong.

Keep in mind that, if you're doing so, and call env->NewLogArray(), you'll 
have to explicitly call System.gc() so memory consume doesn't skyrocket.

HTH,
  Esteve

-- 
Esteve Fernàndez Gonzàlez, Software Engineer

e-mail: [email protected]
phone:  +34 934 230 324
fax:    +34 933 251 028

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