Re: The "Right Way" (TM) to run external program out of gtk2-perl app?

Hi muppet and list,

Am Dienstag 30 August 2005 17:23 schrieb muppet:
Stephan Brunner said:
What is the most safe and clean way of calling convert?
My requirements are
1) portability (Linux + Win32)
2) check exit status of convert
3) no need to write to or read from convert (no pipe needed)
4) UI blocking not nice, but would be acceptable
5) only one instance of convert at a time
6) the subroutine calling convert must not return until convert is done,
because I need to do some updates (ProgressBar, image display, ...)
afterwords, and to hold for 5.

I tried the solution for long-file-reading in the FAQ with
Helper::add_watch, but it doesn't hold for 6). Didn't try it on win32.

To make the long-file-read approach work for 6), you simply need to run a
nested main loop, and kill that nested main loop when the operation is
finished.  Then you can wrap that whole thing up in a function that blocks
from the caller's point of view, but doesn't prevent the main loop from


You said you didn't want pipes, but doing this form of IPC without a perl
pipe open (which perl has conveniently made portable for us) is hard to get
right, using fork(), wait(), SIGCHLD, and all sorts of delicate error

I don't *need* pipes, but I don't mind using one if it works fine.

This solution works nicely for me, and took about five minutes 
to toss together in a working, if primitive, thumbnailer (see attached
file).  Note that i have not tested this anywhere but on my linux desktop
machine; YMMV.

This is quite frustrating, you solving my afternoons problem in five 
minutes:-) The solution you posted works perfect for me on Debian Sarge and 
Windows XP.
I found the reboot-issue not to be connected with this, because I can make my 
machine reboot also by calling "convert" in a (long enough) bash for-loop. 
Anyway, I do now have an always-responsive UI.

Making it possible to kill the child in a 'cancel' action is left as an
exercise for the reader.  ;-)

Hmm, for now, the well-honoured users (that is me, myself and I) will have to 
wait for the last called convert to finish its operation...

I very much appreciate your help, thank you!


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