[squeak-dev] Using OSProcess

David T. Lewis lewis at mail.msen.com
Sat Nov 20 17:07:06 UTC 2010

On Fri, Nov 19, 2010 at 03:56:26PM -0200, Casimiro de Almeida Barreto wrote:
> Em 19-11-2010 15:39, Mike Hales escreveu:
> > Thanks, that's just want I wanted. And thanks Sean for the tip on
> > the http://forum.world.st/ index. That's pretty handy having all the
> > lists together in one spot.
> >
> >
> > Mike
> >
> > Mike Hales
> > Engineering Manager
> > KnowledgeScape
> > www.kscape.com <http://www.kscape.com>
> BTW, if you're running squeak over CogVM it wont work... there are
> incompatibilities between OSProcess, CommandShell and OSProcessPlugin
> and cog.
> Interesting enough, if I do:
> | str |
>     str := (PipeableOSProcess command: 'ls -l') upToEnd.
> It will return and empty ByteString but will fail to read output from
> stdOut.

This is just a timing glitch. Try this instead and I think you will
get the results you want. This works on both Cog and the interpreter VM:

  (PipeableOSProcess command: 'ls -l') upToEndOfFile

Piping to and from an external process can be a bit tricky. A program
like /bin/ls will exit only after you close the pipe to its standard
input (the #command: method does this for you). After that pipe closes,
the /bin/ls program will flush its standard output stream to the
pipe that is connected back to Squeak. Some time after that, the
data will become available for Squeak to read. When you do #upToEnd,
you are reading all available data on that pipe, and if you happen
to read it before it is all available, you get an empty string.
The #upToEndOfFile keeps trying to read until the pipe is actually
closed (when /bin/ls exits), so this makes sure you get all of the
output data even when you are running on a really fast Cog VM :)

> Forking PipeableOSProcess won't work when using cog.
> like:
> ps := PipeableOSProcess forkHeadlessSqueakAndDoThenQuit: [ ... ]
> will fail crashing cog (memory fault). At least under linux.

As far as I know, then only part of OSProcess/CommandShell that
does not work in Cog is the #forkSqueak methods. Unfortunately,
#forkSqueak is used extensively in the unit tests, so be careful
about running those under Cog. But all other OSProcess and CommandShell
functions seem to work fine in Cog.

You may get a warning dialog about AioPlugin not present. This is
because the plugin was not included in the Cog VM, and you can
safely ignore the warning.


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