Re: [Help-bash] backgrounding a process sends it into a tailspin

[Dennis Williamson]

On Sep 11, 2012 7:30 PM, "Cook, Rich" <address@hidden> wrote:
>
> Dang, it's a cluster and I don't have console access -- everything's in an xterm. 

He meant a separate session (terminal window). You'll have to determine its device (use who -utH)

> I tried echoing to a file, and the file was empty:  
> ls -l trapped.txt
> -rw-rw-r-- 1 rcook rcook 0 Sep 11 17:29 trapped.txt
>
> here's the script I ran:
>
> touch /g/g0/rcook/trapped.txt
> for s in $(trap -l | sed 'S/[[:digit:]]\+)//g') ; do 
> trap 'for c in $(jobs -p);do
> echo kill -s '$s' $c >>/g/g0/rcook/trapped.txt
> kill -s '$s' $c
> done' $s
> done 
>
> logger()
>   if [[ -x $IMG_TRACK ]]; then 
>       "$IMG_TRACK" "$1" gnuplot-4.4.3 "$BASH_SOURCE" "$@"
>   fi
>
> IMG_TRACK=${IMG_TRACK:-/usr/local/tools/imgtrack-1.0/bin/imgtrack}
> trap "logger END" EXIT
> logger BEGIN
> # using exec avoids a problem with gnuplot spinning up 100% CPU usage, but disables the "EXIT" trap above.  C'est la vie
>  /usr/local/tools/gnuplot-4.4.3/bin/gnuplot.real "$@"
>
>
> On Sep 11, 2012, at 5:22 PM, John Kearney wrote:
>
>>
>> well you could try
>>
>> for s in $(trap -l | sed 'S/[[:digit:]]\+)//g') ; do
>> trap '
>> for c in $(jobs -p);do
>> echo kill -s '$s' $c >/dev/ttyn
>> kill -s '$s' $c
>> done' $s
>> done
>>
>> basically every signal.
>> and  echo what its doing to ttyn where ttyn is the tty of another console, for debug purposes
>>
>> run pty in a second console to find its device
>>
>>
>>
>>
>>
>> Am 12.09.2012 02:10, schrieb Cook, Rich:
>>>
>>> Sadly, lacking imagination and information, I don't know what other signals to try trapping.  
>>> If I understand correctly, the theory is that readline is being woken from slumber by some signal repeatedly.  
>>> It looks to me more like readline is ignoring an error state.  
>>> I'm 99% sure it's readline because sqlcipher which I also compiled against readline has the same exact issue, I see after playing around with it. 
>>> I'm going to post on the readline mailing list to see what I can learn there.  
>>> Thanks for the help here!  It's been very instructive. 
>>>
>>> On Sep 11, 2012, at 4:59 PM, John Kearney wrote:
>>>
>>>> sry on my bb it autocaps.
>>>> yhea that can't work try instead
>>>>
>>>> #!/usr/bin/env bash
>>>>
>>>> trap '
>>>> for c in $(jobs -p);do
>>>> kill -s SIGTTIN $c
>>>> done' SIGTTIN
>>>>
>>>> logger()
>>>>   if [[ -x $IMG_TRACK ]]; then
>>>>       "$IMG_TRACK" "$1" gnuplot-4.4.3 "$BASH_SOURCE" "$@"
>>>>   fi
>>>>
>>>> IMG_TRACK=${IMG_TRACK:-/usr/local/tools/imgtrack-1.0/bin/imgtrack}
>>>> trap "logger END" EXIT
>>>> logger BEGIN
>>>>  /usr/local/tools/gnuplot-4.4.3/bin/gnuplot.real "$@" &
>>>> wait
>>>>
>>>>
>>>>
>>>> andif that doesn't work 
>>>>
>>>>
>>>> for s in SIGTTIN  SIG.... ; do
>>>> trap '
>>>> for c in $(jobs -p);do
>>>> kill -s '$s' $c
>>>> done' $s
>>>> done
>>>>
>>>> i.e. try propagating other signals
>>>>
>>>> Am 12.09.2012 01:37, schrieb Cook, Rich:
>>>>>
>>>>> Hi, thanks for the suggestion.
>>>>> I tried that (using 'kill' instead of 'Kill' and 'for' instead of 'For') and it did not change behavior, still seems confused.
>>>>>
>>>>> #!/usr/bin/env bash
>>>>>
>>>>> trap '
>>>>> for c in $(jobs -p);do
>>>>> kill -s SIGTTIN $c
>>>>> done' SIGTTIN
>>>>>
>>>>> logger()
>>>>>   if [[ -x $IMG_TRACK ]]; then
>>>>>       "$IMG_TRACK" "$1" gnuplot-4.4.3 "$BASH_SOURCE" "$@"
>>>>>   fi
>>>>>
>>>>> IMG_TRACK=${IMG_TRACK:-/usr/local/tools/imgtrack-1.0/bin/imgtrack}
>>>>> trap "logger END" EXIT
>>>>> logger BEGIN
>>>>>  /usr/local/tools/gnuplot-4.4.3/bin/gnuplot.real "$@"
>>>>>
>>>>> On Sep 11, 2012, at 4:31 PM, <address@hidden>
>>>>>  wrote:
>>>>>
>>>>>> You could try propagating the signal.
>>>>>>
>>>>>> I.E. Add something like this to the start of your script.
>>>>>> trap '
>>>>>> For c in $(jobs -p);do
>>>>>> Kill -s SIGTTIN $c
>>>>>> done' SIGTTIN
>>>>>>
>>>>>>
>>>>>> Cheers
>>>>>> Sent from my BlackBerry device
>>>>>>
>>>>>> -----Original Message-----
>>>>>> From: "Cook, Rich" <address@hidden>
>>>>>> Sender: address@hidden: Tue, 11 Sep 2012 23:24:38
>>>>>> To: <address@hidden><address@hidden>
>>>>>> Cc: address@hidden<address@hidden>
>>>>>> Subject: Re: [Help-bash] backgrounding a process sends it into a tailspin
>>>>>>
>>>>>> Yes, this sounds like a good analysis -- would a patch be in order here?  Can this be fixed?  I know it's an edge case so probably doesn't come up much. 
>>>>>>
>>>>>> On Sep 11, 2012, at 4:14 PM, Chet Ramey wrote:
>>>>>>
>>>>>>> On 9/7/12 8:46 PM, Cook, Rich wrote:
>>>>>>>>
>>>>>>>> Hello,
>>>>>>>> I have built and installed gnuplot and wrapped it in a bash script.  The script simply makes a usage entry in a database, calls gnuplot, then notes that it exits.  I'm including the script below. 
>>>>>>>>
>>>>>>>> When the user runs this script and puts it into the background, gnuplot immediately starts taking up 100% of a CPU, spinning in readline.  This only happens when gnuplot is wrapped in this way, not when it's called directly.  I would like to avoid this behavior, obviously, but I would also like to continue using a wrapper script.  What is it about being called from a script that is causing this odd behavior on gnuplot's part? 
>>>>>>>
>>>>>>> I haven't looked at this at all, but it seems fairly clear that the problem
>>>>>>> has to do with process groups and access to the terminal's foreground
>>>>>>> process group.  gnuplot, not being used to running in the background,
>>>>>>> doesn't have anything to ensure that it's in the right pgrp before
>>>>>>> attempting to use readline to read from the terminal.
>>>>>>>
>>>>>>> The signal that gnuplot gets is most likely SIGTTIN.  If it's not, ignore
>>>>>>> the rest of this.
>>>>>>>
>>>>>>> Starting the script in the background means that it will not be in the same
>>>>>>> process group as its controlling terminal, which will result in SIGTTIN
>>>>>>> every time the process tries to read from the terminal.
>>>>>>>
>>>>>>> The non-job-control shell started to run the script getting in the middle
>>>>>>> between the interactive shell running the script in the background and
>>>>>>> gnuplot is complicating things, but probably not really the problem.  It
>>>>>>> receives the SIGTTIN as well, but should have the disposition set to
>>>>>>> SIG_DFL and get suspended.
>>>>>>>
>>>>>>> Readline catches SIGTTIN so it can clean up the terminal attributes it
>>>>>>> modifies.  It cleans up, ending with a call to tcsetattr from
>>>>>>> rl_deprep_terminal, restores the old signal handler, and unblocks the
>>>>>>> signal, letting it through to the application.  I'm not sure what gnuplot
>>>>>>> does with it then, but I suspect it's catching it somehow and calling
>>>>>>> readline again.
>>>>>>>
>>>>>>> Chet
>>>>>>> --
>>>>>>> ``The lyf so short, the craft so long to lerne.'' - Chaucer
>>>>>>> ``Ars longa, vita brevis'' - Hippocrates
>>>>>>> Chet Ramey, ITS, CWRU    address@hidden    http://cnswww.cns.cwru.edu/~chet/
>>>>>>
>>>>>> --
>>>>>> ✐Richard Cook  
>>>>>> ✇ Lawrence Livermore National Laboratory
>>>>>> Bldg-453 Rm-4024, Mail Stop L-557       
>>>>>> 7000 East Avenue,  Livermore, CA, 94550, USA
>>>>>> ☎ (office) (925) 423-9605   
>>>>>> ☎ (fax) (925) 423-6961
>>>>>> ---
>>>>>> Information Management & Graphics Grp., Services & Development Div., Integrated Computing & Communications Dept.
>>>>>> (opinions expressed herein are mine and not those of LLNL)
>>>>>>
>>>>>>
>>>>>>
>>>>
>>>>
>>>> --
>>>> <btn_profile_greytxt_80x15.png> <10_en_btn.gif> <button_logo.png> <youshi_logo.png>
>>>
>>>
>>> -- 
>>> ✐Richard Cook   
>>> ✇ Lawrence Livermore National Laboratory
>>> Bldg-453 Rm-4024, Mail Stop L-557        
>>> 7000 East Avenue,  Livermore, CA, 94550, USA
>>> ☎ (office) (925) 423-9605    
>>> ☎ (fax) (925) 423-6961
>>> ---
>>> Information Management & Graphics Grp., Services & Development Div., Integrated Computing & Communications Dept.
>>> (opinions expressed herein are mine and not those of LLNL)
>>>
>>>
>>>
>>
>>
>> --
>> <btn_profile_greytxt_80x15.png> <10_en_btn.gif> <button_logo.png> <youshi_logo.png>
>
>
> -- 
> ✐Richard Cook   
> ✇ Lawrence Livermore National Laboratory
> Bldg-453 Rm-4024, Mail Stop L-557        
> 7000 East Avenue,  Livermore, CA, 94550, USA
> ☎ (office) (925) 423-9605    
> ☎ (fax) (925) 423-6961
> ---
> Information Management & Graphics Grp., Services & Development Div., Integrated Computing & Communications Dept.
> (opinions expressed herein are mine and not those of LLNL)
>
>
>