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From "Andrew Zhang" <zhanghuang...@gmail.com>
Subject Re: [classlib][NIO|VMI]JNI 1.4 enhancement on ByteBuffer
Date Wed, 14 Jun 2006 01:15:42 GMT
On 6/13/06, Paulex Yang <paulex.yang@gmail.com> wrote:
> There is some enhancement on JNI spec in JDK 1.4[1], and three methods are
> related to java.nio.ByteBuffer.
>    * |NewDirectByteBuffer|
>      <
> http://java.sun.com/j2se/1.4.2/docs/guide/jni/jni-14.html#NewDirectByteBuffer
> >
>    * |GetDirectBufferAddress|
>      <
> http://java.sun.com/j2se/1.4.2/docs/guide/jni/jni-14.html#GetDirectBufferAddress
> >
>    * |GetDirectBufferCapacity|
>      <
> http://java.sun.com/j2se/1.4.2/docs/guide/jni/jni-14.html#GetDirectBufferCapacity
> >
> Because these methods are actually classlib dependent and JNI
> implementation must know some details of ByteBuffer implementation, current
> IBM VME hasn't them implemented, and seems DRLVM doesn't implemented
> thoroughly(please correct me if I made mistake here, seems DRLVM tries to
> get some non-api method/field of ByteBuffer, and if fails, it return NULL or
> -1 as JNI spec says). And I have no idea how Sable/JCHEVM/BootJVM deals with
> this issue yet.(anyone kindly let me know?)

I propose to provide the implementation in NIO component, and I raise
> Harmony-578 for it. The idea is: export these three methods in NIO module as
> hynio.dll(.so), which is loaded by Harmony launcher, and add these methods
> to VMI in some way, so that the VM vendor(i.e., JNI implementation vendor)
> can add these methods to JNI function table.
> Other choices I can imagine now include:
> 1. Add related direct buffers class to kernel class, so that the VM vendor
> can implement it as well as the JNI methods. IMO this is not good choice
> because buffers are actually VM independent, it's not reasonable to let VM
> vendor to implement these classes.

It seems that JCHEVM follows this way. It depends on classes from classpath

2. Provides some utility methods in o.a.h.nio, add these methods to VMI, so
> that VM vendor can get inside knowledge on the direct buffers by these
> utilities. This option is acceptable, but it also needs to modify VMI, and
> the modification is based on some Harmony specific contract, while my
> proposal above is based on public JNI spec, so this one is not preferred.

It seems that DRLVM follows this way, except it assumes the utility methods
are located in java.nio.ByteBuffer, not o.a.h.nio.

Any ideas and comments are highly welcome.
> [1]http://java.sun.com/j2se/1.4.2/docs/guide/jni/jni-14.html
> --
> Paulex Yang
> China Software Development Lab
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Andrew Zhang
China Software Development Lab, IBM

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