[SAGA-RG] minutes from the OGF21 session on the Java language binding

[Thilo Kielmann]

Minutes of the meeting of SAGA-RG
held at OGF21, oct 17, 2007, 15:15-16:45

notes: Shantenu Jha, Thilo Kielmann

agenda:

1. IPR
2. Agenda bashing
3. Java binding for the CORE spec

Thilo Kielmann opens the session, explains the IPR rules and hands out
the signup sheet

It is agreed to begin the session with a short report-out from the
"future of DRMAA" session.
Here, Dan Templeton reports about the plans to prepare a next DRMAA
version as another SAGA package.
Both the SAGA and DRMAA groups want to cooperate on this issue.

Java binding:

Thilo Kielmann is presenting important aspects of the Java binding, as
it is currently being developed by his group.

fundamental decisions:

- design for Java 1.5
- for application portability across multiple implementations, a mechanism
  like C++ header files is desirable. for this purpose, the language binding
  presents all SAGA interfaces and classes as interfaces, accompanied by
  factory classes. These interfaces and classes will have to be used by all
  implementations, acting like header files.

Flags being used, e.g. for file read/write/create operations.
-----
The current soluton is based on enumerations. The participants doubt that
this solution is ideal. Use of these enumerations is complex due to the
method interface of the object. Also, these enums are converted to integers
for the operations (e.g., file read); this violates type safety.

The participant discuss alternatives for modeling such flags. They favour
two options:
a) a pure integer-based solution without type safety, but with an easy to use
   interface and predefined constants (powers of two)
b) a real object that never gets casted to integers

Proposals for both versions shall be made and posted to the mailing list for
comparison and for adopting one of these two approaches.

timeout values:
--------------
numeric constants such as "nowait" and "waitforever" shall be used instead
of 0 and -1

Buffers:
-------

it is suggested to check whether the NIO bytebuffer could be used instead of
a from-scratch buffer


files:
-----
SAGA files are POSIX style
the Java binding is using exceptions instead of the POSIX error codes
The current file implementation is inspired by random files.
inputstream and outputstream shall be layered on top of this.

tasks:
-----

this interface (group) seemingly needs more attention

it is suggested to check whether future objects from the concurrency library
could be used.
the RVTask looks very much like a future

the asymmetry between run() and waittask() should be resolved


optional parameters:
-------------------

it is suggested to add methods (via overloading) that do not have the last
parameter for those methods with optional parameters in the SAGA CORE spec.
maybe the varargs mechanism might help (whatever becomes easier to use)


implicit sessions:
-----------------
in SAGA, the default session is used unless specified differently.
this means that the factories need additional methods without session
parameters.


RPC package:
-----------

esp here, the varargs package might be useful


CPI, adaptor interface:
----------------------

The audience suggests to add an SPI (service provider interface) as part
of the Java language binding (currently called CPI in the JavaGAT)
This could allow for a standardized adaptor interface, and thus adaptor
reuse.
Good examples for such an API/SPI combinations are: JAXP, LDAP, DRMAA


multiple implementations:
------------------------

the questions was raised whether it would be / should be possible to
use multiple SAGA implementations in the same application.
It was decided to not support this as no real need is seen.

thread safety:
-------------
The audience decided that simply requiring thread safety (and synchronization)
of SAGA methods would simplify application development. An expected 
performance impact is considered of lesser importance, as the service times
of remote services dominate invocation times anyway.