Paulex Yang 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.
By reading the spec, it seems RI prefer this way, take direct-buffer as
kernel class ,like class String(Though maybe it is hard to tell "kernel"
and "normal" classes in RI's implementation, they're always together
there :) ).
And in Harmony, there's an interface named "DirectBuffer"
(o.a.h.nio.internal), abstract class Buffer(java.nio) and an
implementation class "ReadWriteDirectByteBuffer" (java.nio),which
contains fields and methods for JNI methods. So an easy way may be: take
these "as" kernel classes, and get Address from
DirectBuffer.getBaseAddress(), get Capacity from Buffer.capacity, and
new a ReadWriteDirectByteBuffer as basic direct buffer in three JNI methods.
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
--
Best Regards!
Jimmy, Jing Lv
China Software Development Lab, IBM
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