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From Gregory Shimansky <gshiman...@gmail.com>
Subject Re: [DRLVM][JNI]GetByteArrayRegion differs from RI (was Re: Exceptions found while running servlet...)
Date Mon, 14 Aug 2006 20:03:45 GMT
On Monday 14 August 2006 23:37 Geir Magnusson Jr wrote:
> > I've written a test [1] myself and cannot say I completely understand the
> > result. With length = 0 RI 1.5 allows calling to Get<type>ArrayRegion
> > with start equal to array length but throws AIOOBE if start is greater
> > than array length.
>
> That makes sense to me, only because I am thinking of j.i.OutputStream's
> write([], int, int) method, which does state that it's ok if start + len
>  == arraylen...

It is not specified either, is it? I looked at the 
ObjectOutputStream.write(byte[], int, int) and didn't find any detailed 
description about allowed ranges.

> I'm sure if we thought about it, we'd figure out that it lends itself
> nicely to some common loop idiom. I suspect it will be some end case
> when some read returns an empty buffer, so
>
>   write(buf, 0, 0)
>
> works without a check, or some situation where there's some post
> decrement leading you to
>
>   write(buf, length, len)
>
> where the len was calculated from (buf.length - length) or something.
>
> Now, that isn't what the JNI spec says, but it seems like the JNI spec
> was written in a hurry... :)

JNI spec is indeed quite incomplete when it comes to border cases. Sun 
wouldn't need to create a special book [1] (however this clarification  
doesn't clarify this particular case) for JNI clarification if they wrote a 
complete spec from the start.

However Sun usually changes a spec if its implementation doesn't work 
according to it for some time. JNI spec is really old, it was written for 1.1  
and the statement about exception still remains.

> > I am unsure if we want to allow this compatibility and a reason to allow
> > it. When length is 0 the application still gets nothing except for clear
> > exception status. There is no value in allowing this call except for
> > allowing software which has a bug in it to work. On the other hand
> > allowing start == length to pass violates the spec IMHO.
> >
> > I think it is better if software which uses this undocumented feature was
> > fixed instead of introducing this workaround, so if others agree I think
> > HARMONY-1156 could be closed.
>
> Well, I don't feel strongly either way, but am uncomfortable with the
> inconsistency.  The JNI docs seem pretty sparse, and clearly some
> thought went into allowing :
>
>   write( buff, buff.length, 0)

The whole exception condition looks like this

    jsize length = GetArrayLength(env, array);
    jsize end = start + len;
    if(start < 0 || start >= length || end < 0 || end > length) {
        char msg[30];
        sprintf(msg, "%d..%d", start, end);
        ThrowNew_Quick(env, "java/lang/ArrayIndexOutOfBoundsException", msg);
        return;
    }

and it is easy to change start >= length to start > length if you ask for it. 
I am still unsure if this is a place where spec should step away from the 
spec be it imcomplete or not. Programmers who don't work for Sun read public 
spec, don't they?

[1] http://java.sun.com/docs/books/jni/html/jniTOC.html

-- 
Gregory Shimansky, Intel Middleware Products Division

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