Re: Java Native Interface?

[Jon.Paris@xxxxxxxxxx]

As at V4R4, using JNI with RPG is best suited for people whose idea of a good
time is to walk naked over broken glass while lashing themselves with razor
wire.  All of this taking place in a snowstorm in the midst of a Rochester
winter.  It is a painful process and I recommend people to wait until the
compiler provides more direct support in a later release.

That said, if you are really in a masochistic mood, the major problems are
concerned with thread safety.  Java is inherently multi threaded, RPG is not,
and more specifically the runtime is not fully thread safe.  The V4R4 support
allows RPG to operate in a multi threaded environment by serializing access to
the _module_ i.e. once any procedure in a module is active, then no other
procedures in that module can be invoked.  This causes design problems in a
variety of areas including the possibility of encountering a deadly embrace.
Here's an example -  In thread 1 Proc A in module X calls Proc B in module Y.
Meanwhile in thread 2 Proc C in module Z wants to call Proc D in module X.
Thread 2 will be made to wait until thread 1 frees the lock on module X.  So far
so good, but what if thread 1 decides to call Proc E in module Z?  That module
is locked by thread 2 which can't complete until thread 1 releases its lock
which ..............


This has an effect on your design - you might be tempted to have one procedure
per module for example.  This in turn might make you look to using Import/Export
to share data between procedures (or ... shudder .... the LDA!) that would
otherwise have been global data in the same module.  Now you have to worry about
the possibility that multiple threads could be trying to update the same piece
of data at the same time and the system can't protect you against that.

The net of it is that you have to give considerable thought to your design and
whether the payoff (compared with say a simple toolbox program call) is worth
the effort.


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