Development Tools Forum

Re: Java with informix 4gl shared objects

Posted By: Jonathan Leffler
Date: Saturday, 18 March 2006, at 11:31 p.m.

In Response To: Java with informix 4gl shared objects (MARK TYRER)

On 3/13/06, MARK TYRER <m_tyrer@hotmail.com> wrote:
> Tried posting to the classics sig - and they suggested that I try this one.
>
> I have a need to expose functions within an informix shared object (compiled
> with informix 4gl 7.3 running against informix 7 db) to Java. The need is such
> that I must be able to call the java classes remotely. Currently I have been
> able to create a JNI wrapper for the shared object and am able to connect
> using RMI. For a performance test, I iterated a simple function, a 1000 times
> without a problem. However, as soon as I try to connect with a second session
> (Running the same performance test), The java server class falls over because
> the shared object reports a -439 error.

Are you using threaded Java? I4GL code is not designed for use in
threaded programs, and does not use thread-safe ESQL/C libraries.
That could be the first problem - or it might be irrelevant.

What is the message for error -439? Most people don't recall all the
error messages (not even I do) and I had to go look it up. Please
review: http://www.catb.org/~esr/faqs/smart-questions.html for a
discussion on this.

-439 Database server is currently processing an SQL task.

This sounds ominously like a multi-threaded application trying to use
the same connection for two different tasks at the same time. Failing
that, it means that you somehow not waiting for the server to complete
one task on the connection before attempting to do a second, and that
normally implies multiple threads of control.

> My java is a little shakey at best, so the answer may be staring me in the
> face. (Here is what I suspect - not what I know) However, my suspision is that
> the rmiregistry is a single process on the host box and runs the server
> classes. I think that when I run the native function an informix connection is
> formed. When the second connection runs, It utilises the already formed
> informix connection and causes a conflict.

It is not clear to me what you mean by 'the second connection'; it
seems to be something different than an 'Informix connection'.
However, if you have a process 'rmiregistry' that is running the I4GL
library on your behalf, then you need to be sure that you understand
the I4GL and the ESQL/C models for supporting threaded applications.
The I4GL support is simple to explain - there is no support in plain
I4GL for threaded applications. What's more, it would be fairly hard
to add it; there are rather too many global variables lurking around
in the I4GL runtime support library - let alone in the typical piece
of I4GL code - for it to be safe for multi-threaded use.
Consequently, you would need to ensure that the code that invokes I4GL
functions keeps the I4GL library single-threaded - presumably you'd
need to code some sort of mutual exclusion system (a mutex) so that if
one piece of Java is running an I4GL function, all other pieces of
Java are kept out. Even with that mutual exclusion handled, there is
a large probability that two separate Java threads will interfere with
each other. For example, if two Java threads tried to run the same
report at the same time, they would seriously interfere with each
other - you would have to ensure that only one Java thread has a given
report in the 'report started' state (pending FINISH REPORT or
TERMINATE REPORT) at any time; the second thread must either be given
an error (report is busy) or held up until the report is not busy.

You can use multiple connections in I4GL, but the ESQL/C libraries it
uses is not the thread-safe library, so you can only synchronously
switch between the connections. In a thread-safe ESQL/C application
(linked with the thread-safe ESQL/C libraries), you should ensure that
any given connection is used by one thread at a time - and be
extremely careful about which connection each statement was prepared
on, etcetera.

> Has anyone out there managed to get this kind of scenario to work?

No, but neither have I tried. By the resounding silence, I suspect
most other people have not tried either. Consequently, what I said
above is hypothesis, not proven.

--
Jonathan Leffler #include <disclaimer.h>
Email: jleffler@earthlink.net, jleffler@us.ibm.com
Guardian of DBD::Informix v2005.02 -- http://dbi.perl.org/

Messages In This Thread

• Java with informix 4gl shared objects
  MARK TYRER -- Monday, 13 March 2006, at 4:22 a.m.
  • Re: Java with informix 4gl shared objects
    Jonathan Leffler -- Saturday, 18 March 2006, at 11:31 p.m.
    • Re: Java with informix 4gl shared objects
      sergio@moredata.pt -- Monday, 20 March 2006, at 4:43 a.m.
      • RE: Java with informix 4gl shared objects
        Rivka Shisman -- Tuesday, 21 March 2006, at 4:24 a.m.

Development Tools Forum is maintained by Administrator with WebBBS 5.12.