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.
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.
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
IBM
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