On Tue, Dec 23, 2008 at 10:59 PM, John Caron <caron@xxxxxxxxxxxxxxxx> wrote:
> Hi Arlindo:
>
> There is no such low level C-like API in the netcdf-Java library. However,
> the Java API has a pretty close correspondence, but an automatic conversion
> is not likely.
I was thinking about doing this by hand...
>
> If what you need is netcdf + opendap in C, then you can use netcdf-4. Im not
> sure what the release status of that is, but i know you could get a
> preliminary version.
>
> OTOH, Im not sure exactly what you are trying to accomplish. Take existing C
> code using netCDF C library and turn into Java? For what purpose?
>
The NestedVM project
http://nestedvm.ibex.org/
provides means of compiling C sources into Java byte code. This is
accomplished by compiling C sources into mips machine code and then
translating this into java byte code. In this sense, the JVM becomes
another platform to build for; no translation .c to .java is
necessary. There is only one set of sources to maintain, and a java
version of your application comes with very little development
overhead.
With relatively moderate effort, I've been able to produce a very
functional build of the latest GrADS v2 release that runs entirely
under the JVM; no JNI involved, 100% pure JVM. This includes full
NetCDF-3, HDF-4, GRIB-1, GRIB-2 and PNG support. Except for rewriting
the low level graphics primitives to use awt/swing, no manual java
recoding was necessary. The only major feature missing in this build
is OPeNDAP support. Of the OPeNDAP dependencies, I've been able to
build xml2, but curl has been a bit trick because some of the syscalls
needed are yet to be implemented in NestedVM (I'm getting close,
though: curl builds and runs under the JVM but does not quite work
yet.)
As a stop-gap measure, I was considering wrapping your NetCDF-Java
classes to provide an implementation of the few low-level nc-dap
calls that are used by grads. (Nested VM allows for you to call Java
native methods from your "C" code.) Since other folks might have
already done this work, I was trying not to duplicate any effort. As
you indicate, there is good correspondence between the Java and C
APIs, and although tedious this seems quite doable.
At some point I'd interested in benchmarking my NestedVM build of
NetCDF-3 against our native implementation. I've been very surprised
by the performance of NestedVM.
Cheers!
Arlindo
> Regards,
>
> John
>
> Arlindo da Silva wrote:
>> Hi,
>>
>> I am in the process of using NestedVM (uses gcc to compiles C
>> sources into JAVA bytecode, see http://nestedvm.ibex.org/) to port
>> some C code to Java. I've been able to compile the latest NetCDF 3.x
>> code just fine, but I need OPeNDAP and nc-dap is a bit more
>> challenging as I need to implement a fairly functional ipc/xdr layer
>> for that. Therefore, I could save time by calling NetCDF-Java
>> implementation instead.
>>
>> I only need to read classic NetCDF-3 files/OPeNDAP URLs, therefore
>> the immutability of the file object in NetCDF-Java should not be a
>> concern. Has anybody developed a wrapper (or does it exist privately
>> inside NetCDF-Java) for NetCDF-Java with a C-Like API? Say,
>> nc_open(), nc_close, etc. I'm trying not to reinvent the wheel...
>>
>> Thank you,
>>
>> Arlindo
>>
>
--
Arlindo da Silva
dasilva@xxxxxxxxxxxx
