frysk and jython (Java Python)

[Andrew Cagney <cagney at redhat dot com>]

Here's a little proof-of-concept showing jython (http://www.jython.org), 
the Python interpreter that works with Java, interacting with the frysk 
core.

I've included a running commentary (and I appologize in advance for my 
clear lack of Python foo :-), here goes:


The build system creates a little script gij.sh 
($BUILD/frysk-core/gij.sh) that wraps frysk up so that it looks like a 
java byte code interpreter.  Use that to load/run the jython interpreter:

> cagney@localhost$ CLASSPATH=/usr/share/java/jython.jar ./gij.sh 
> org.python.util.jython
> Jython 2.2a0 on java1.4.2 (JIT: null)

Grap the process model's Manager, it knows were a few key things are; 
tell it to kick off the event-loop thread.

> >>> from frysk.proc import Manager
> >>> Manager.eventLoop.start ()

> >>> h = Manager.host

Grap this machines Host.  Since frysk is self-aware (it knows the 
location of itself within the host's process hierarchy), start examining 
the process model by looking at frysk.

> >>> me = h.getSelf ()
> >>> print me
> {frysk.proc.LinuxProc@1226d58,id={ProcId,26184},state=unattached}

> >>> print me.getCommand()
> fryski

That's frysk built as a java interpreter.

> >>> print me.getTasks()
> [Linux{frysk.proc.LinuxTask@37a550,id={TaskId,26186},proc={frysk.proc.LinuxProc@1226d58,id={ProcId,26184},state=unattached},state=unattached}, 
> Linux{frysk.proc.LinuxTask@37a5a0,id={TaskId,26185},proc={frysk.proc.LinuxProc@1226d58,id={ProcId,26184},state=unattached},state=unattached}, 
> Linux{frysk.proc.LinuxTask@37a5f0,id={TaskId,26184},proc={frysk.proc.LinuxProc@1226d58,id={ProcId,26184},state=unattached},state=unattached}]

"task" is the linux kernel concept of a thread of execution; NPTL is 
implemented as a very thin layer over these tasks.  This process has 
three tasks: main (running the interpreter); the frysk event loop; and 
the garbage collector.

> >>> h.requestCreateAttachedProc (["sleep","1000"])

Tell the host to kick of a new process.  Since frysk started it, it, as 
expected, appears below frysk in the process tree.  Use sleep, so that 
the running process hangs around long enough for us to see it (by 
default everything is allowed to run):

> >>> me.getChildren()
> [{frysk.proc.LinuxProc@1226b28,id={ProcId,26187},state=startRunning}]
> >>> child = me.getChildren()[0]
> >>> print child.getTasks()
> [Linux{frysk.proc.LinuxTask@37a3c0,id={TaskId,26187},proc={frysk.proc.LinuxProc@1226b28,id={ProcId,26187},state=startRunning},state=running}]
> >>> child.getCommand()
> 'sleep'

Finally, lets look above frysk to see where this process sits within the 
process tree; iterate over the parents until the top-most process is 
reached:

> >>> p = me
> >>> while p:
> ... print p
> Traceback (innermost last):
>   (no code object) at line 0
>   File "<console>", line 2
>         print p
>         ^
> SyntaxError: invalid syntax
> >>> while p:
> ...     print p
> ...     p = p.getParent ()
> ...
> {frysk.proc.LinuxProc@1226d58,id={ProcId,26184},state=unattached}
> {frysk.proc.LinuxProc@1226d90,id={ProcId,13825},state=unattached}
> {frysk.proc.LinuxProc@1226dc8,id={ProcId,2781},state=unattached}
> {frysk.proc.LinuxProc@1226e00,id={ProcId,1},state=unattached}
> >>>

(did I mention my lack of Python foo? :-) Looking good.

What next?  There are obviously a number of issues that will need to be 
addressed before this concept can be considered for mainline 
integration.  Of those, several are worth mentioning:

- the graphical interface requires the addition of a per-interpreter / 
cli console window to wrap an interpreter thread
(yes, there is nothing technically stopping frysk from running multiple 
interpreters simultaneously).

- since frysk's core is both non-blocking and event-driven, requests 
such as requestCreateAttachedProc are processed asynchronously (ack 
comming back via an observer); an interpreter's life will be easier once 
the asynchronous interfaces are extended to include synchronized variants.

If you're interested in playing, the frysk interfaces are described in 
http://sourceware.org/frysk/javadoc/public/ ; they will obviously 
continue to rapidly evolve.

Andrew