[kepler-dev] Combining the CommandLine and Exec actors

[Bertram Ludaescher]

Dan Higgins writes:
 > Bertram,
 >     Thank you for reminding me of the '&' option; frankly, I had 
 > forgotten that possibility.

yeah, those good old unix days ;-)


 >  Incidently, the Windows equivalent is 
 > 'start'; i.e.
 > 'start acrobat' in the CommandLine actor will launch acrobat. The Java 
 > method 'exec' which creates a new process in the Command Line actor 
 > waits until the process finishes to return in the current 
 > implementation, but what I forgot is that the process is the commandline 
 > processor. That process will start a new background process which keeps 
 > running and then immediately returns when '&' or 'start' is used.
 >     The problem with this approach is that this secondary process is 
 > completely independent (i.e. no process id is returned to java as far as 
 > I can determine). Thus Kepler has no way to reference the background 
 > process. This is not always a problem. An use that I was thinking of is 
 > using other applications to display outputs - e.g. showing results in 
 > some other application such as using Acrobat to display pdf or 
 > Illustrator to show SVG files. It is somtimes desirable to launch such 
 > independent processes from within Kepler. (However, getting the results 
 > of such independent processes back into Kepler might be problematic.)

BTW, as you probably know, in a Unix shell you can "get back control"
after sending a job to the background (either with '&' or with C-z
(suspend) followed by 'bg') with the command 'fg' (foreground). 
I think a job number might be given as an optional argument..
Even if you don't "reclaim control", some sort of exit code is
displayed when the job finishes (if I remember right).

So maybe this functionality could be useful to build into an actor!? 

 >     Incidently, there is an 'Interactive Exec' actor in Kepler now which 
 > I created some time ago for an interactive R example. In this case, the 
 > process launched by java keeps running as a direct subprocess of the 
 > Kepler java process. (see the InteractiveR.xml workflow.) This didn't 
 > require any special director (it uses SDF). It keeps R running so that a 
 > series of commands can be entered using the InteractiveShell actor. In 
 > this case, the actor can keep track of the direct process launched by 
 > Interactive Exec because that process is directly executed (rather than 
 > indirectly through the command processor).

right. But this happens all within a single firing round, right?

Bertram


 > 
 > Dan
 > 
 > Bertram Ludaescher wrote:
 > 
 > >Dan, Bilsay et al:
 > >
 > >In order to return control immediately w/o waiting for the initiated
 > >command/subprocess to finish, it should be possible to use "&", at
 > >least in Unix-style systems, right? 
 > >
 > >So the good old 
 > >	$ myjob & 
 > >would run myjob in the background. 
 > >
 > >But then again, for platform independence it might be better to have a
 > >parameter to the Cmd-Line actor that determines whether control is
 > >returned immediately (a la "backgrounding") or after command
 > >completetion. 
 > >
 > >Ptolemy-hackers: 
 > >
 > >Are there any directors (or could one conceive variants of the
 > >existing ones) that are particularly well-suited/well-behaved with
 > >Command-Line actor instances that return immediately? 
 > >
 > >Bertram
 > >
 > >Dan Higgins writes:
 > >..
 > > > Finally, one option that I don't think we have considered in Exec or 
 > > > CommandLine is to launch a process and NOT wait for it to complete. 
 > > > (Currently I think we always use a 'waitFor()' method). This would be 
 > > > primarily of use for launching completely different applications for 
 > > > output/display at the end of a Kepler workflow. There are some occasions 
 > > > when this would be useful.
 > >...
 > >  
 > >