Re: gSystem->Exec and background processes

Thanks a lot! I have tested this solution on "root-3/4/5" with "Fedora-Core-3" and "SLC3" and it always worked fine. Cheers
Diego

On Tue, 12 Jul 2005, Paul Russo wrote:

> Diego,
>
> This is a problem with the way root is handling the terminal
> input. Fortunately there is a workaround:
>
> root [0] gSystem->Exec("root -q dummyloop.C < /dev/zero &")
>
> The changes are:
>
> 1. You should give root the -q option to prevent the
> second copy of root from prompting you for more input.
>
> You may also want to give the -l option to prevent
> the second copy of root from putting up the logo
> window.
>
> 2. You do not need to quote the macro filename (you can
> if you want to, but it is not necessary).
>
> 3. Redirecting standard input to come from /dev/zero
> prevents root from reading an end-of-file indicator
> from the detached terminal in the gSystem->ProcessEvents()
> call in your macro. It was this end-of-file indicator
> which caused the second copy of root to exit too soon.
>
> We should be able to fix the underlying problem in the next
> version of root so this workaround will not be necessary in
> the future.
>
> -- Paul Russo
>
> --------<original message follows>
>
> Hi, I'm trying to upgrade my code to root-4.04/02 on
> "Scientific Linux CERN Release 3.0.5 (SL)".
> "gcc version 3.2.3 20030502 (Red Hat Linux 3.2.3-52)"
>
> I found a problem while trying to run another root process with the
> command "gSystem->Exec".
> I attach a simple macro (dummyloop.C) as an example:
>
> [my_shell]$ root
> root [0] gSystem->Exec("root \"dummyloop.C\"&")
>
> The process starts, but it is immediately killed: here is the output of
> the "ps ux | grep root" command:
>
> user 23011 0.0 0.1 3468 1264 pts/6 S 19:17 0:00 root
> user 23012 3.0 2.4 45000 24988 pts/6 S 19:17 0:00 /usr/local/root/bin/root.exe -splash
> user 23019 1.0 0.1 3464 1256 pts/6 S 19:17 0:00 root -q dummyloop.C
> user 23020 22.0 0.0 0 0 pts/6 Z 19:17 0:00 [root.exe <defunct>]
>
> This does not happen if I run the process using the command (without the
> "&"):
> root [0] gSystem->Exec("root \"dummyloop.C\"")
>
> Anyway I need to use the "&" in order to keep on working.
>
> I did not find the problem in root-3.10/02.
> Is there any way to do this in root-4.04?
>
> Thanks in advance.
> Diego
>
> --------<copy of dummyloop.C follows>
>
> {
> for(Int_t i=0;i<20;i++){
> TCanvas *c1 = new TCanvas();
> gSystem->ProcessEvents();
> cout << "ciao " << i << endl;
> gSystem->Sleep(500);
> }
>
> }
>
Received on Tue Jul 26 2005 - 20:09:06 MEST