Re: why does NSTask setpgrp on sub processes?

[Derek Zhou]

On Wednesday 20 January 2010 03:36:49 am Richard Frith-Macdonald wrote:
> 
> On 20 Jan 2010, at 09:48, Derek Zhou wrote:
> 
> > Oops, hit send too soon.
> > 
> > #import <Foundation/Foundation.h>
> > 
> > int main(int argc, char** argv)
> > {
> >  NSTask* editor = [NSTask new];
> >  [editor setLaunchPath: @"vi"];
> >  [editor launch];
> >  [editor waitUntilExit];
> >  NSLog(@"finished\n");
> > }
> > 
> > with the setpgrp (current behavior) it will hang because vi cannot get hold 
> > of the tty. 
> > without the patch which basically disable setpgrp vi will show and after 
> > you close vi
> > this program will exit.
> > I can add tcsetpgrp after the launch so vi can get hold of the tty but then 
> > after vi 
> > exit tty control is not back to my prog but the shell. I have to fg or send 
> > SIGCONT
> > to continue my prog.
> > I see what you mean, currently it is trying to send signal to the new 
> > group. 
> > But how many cases you really want to do that instead of just sending to 
> > the single 
> > process? Also by default if parent got killed all children got killed 
> > (SIGHUP? I 
> > am not sure) so the behavior is still roughly unchanged.     
> 
> After looking at and trying out the above program, it seems there was a 
> problem, but your diagnosis was wrong.
> 
> The issue was not that NSTask changes the process group (which it should), 
> but rather that it was failing to detach the process from the controlling 
> terminal (except when using pseudo-terminals).  I have copied the code used 
> with pseudo terminals so that it's always used.
I see you added the setsid and terminal detach and my program works. The minor 
annoyance of having the launched task in a new session and group is that 
standard shell job control (^Z, jobs, fg, bg) does not work; I'd have to 
send signal to the process manually . Well I guess that's the price you pay 
if you have to be compatible with the "golden" standard. Thanks for the 
quick fix!
Derek

ps: I think you want this:

Index: configure.ac
===================================================================
--- configure.ac        (revision 29340)
+++ configure.ac        (working copy)
@@ -938,7 +938,7 @@
 #--------------------------------------------------------------------
 # These functions needed by NSTask.m
 #--------------------------------------------------------------------
-AC_CHECK_FUNCS(killpg setpgrp setpgid)
+AC_CHECK_FUNCS(killpg setpgrp setpgid setsid)
 if test "x$ac_cv_func_setpgrp" = xyes; then
   AC_FUNC_SETPGRP
 fi