QProcess vs K3Process

Oswald Buddenhagen ossi at kde.org
Tue May 29 22:17:52 BST 2007

On Tue, May 29, 2007 at 10:31:55PM +0200, Thiago Macieira wrote:
> > if timing matters, a common os-level channel is a must.
> Well, if timing matters, why are you running a separate process? With
> pipes no less? Shouldn't a thread be faster?
i didn't think about performance. if processes are concurrently
outputting stderr, the order of the messages might provide essential
another use case might be two processes outputting to a third process
(whether they coordinate or do it line-wise in random order is
irrelevant for the third process).

> >this time i *really* attached the mail to tt. (hey, i *did* say that i'm
> >in a hurry :)
> User-Agent: Mutt/1.5.15 (2007-04-13)
> Start using KMail :-)
i knew somebody would say that. :-P
when it provides an ui i can use over ssh without an x server. ;)
actually, i can have this "you wanted to attach something, bonehead!",
too, but i'm too lazy to set it up. :}

> >> Start every one? Yes, I think you want that. And it isn't difficult
> >> anyways, nor is there a particular order in which they must happen.
> >> The pipes are created when first needed and the remote end is open
> >> when the application starts (either in the parent or in the sibling
> >> process).
> >
> >yes, but why would you *want* to do it separately for every one?
> It takes the same number of lines or less.
> 	QProcess a, b, c;
> 	// set up the pipeline
> 	a.start("foo");
> 	b.start("bar");
> 	c.start("baz");
> or:
> 	QProcess a, b, c;
// set up programs
> 	KProcessGroup pg;
> 	// set up the pipeline
> 	a.joinProcessGroup(&pg);
> 	b.joinProcessGroup(&pg);
> 	c.joinProcessGroup(&pg);
> 	pg.start();	// or a.start();
think a bit further. ;)

KProcesGroup pg;
KProcess a(&pg), b(&pg), c(&pg);
// set up programs
// set up pipeline


KProcessGroup pg;
pg << (QStringList() << "ls" << "-l");
pg << "less";

of course, waitForStarted()/waitForFinished() and even handling have to
be done for every process, too. this is very boring work and prone to
c&p-errors, simple logic errors, etc.
wouldn't you think KProcessGroup would be nice to have? ;)

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