News Group Posts

output buffer flush

From: Barry Margolin <barmar@genuity.net>
Subject: Re: Please help on "kill process"...
References: <268283d.0205171252.7ef8e547@posting.google.com>
<3CE5738F.20807@aplawrence.com> 
Date: Fri, 17 May 2002 22:10:42 GMT

In article <3CE5738F.20807@aplawrence.com>, Tony Lawrence  <tony@aplawrence.com> wrote:
>rak wrote:
>> The process I want to stop is a test program, it will keep running for
>> 5 hours and I redirect the output to a data file. The problem is, the
>> program can only be stopped by press "F3" key. If I use kill to stop
>> it, the last few line of data will not be able to save to my data
>> file. and if I manually run it and press F3 to stop it, the data file
>> is OK. or if I don't redirect the output in the scripts, the full
>> output from the program will shown on screen, even I use kill to stop
>> it. So, how could I use scripts and save all the output into data
>> file?
...
>When you use kill -9, your program has no chance whatsover to clean 
>itself up.  If it is well written, it should flush and close its files 
>on a kill -15 or kill -1.  At least it has the opportunity to do so with 
>those signals; with -9 it has no choice.

Most programs don't contain any special handling of those signals, so it
probably won't help to change the signal.  It's still a good idea, though;
kill -9 should only be used as a last resort for a process that won't die
any other way.

The reason this is happening is most likely that the program uses stdio.
When its output is not to a terminal, it's fully buffered, and when the
process is killed it doesn't flush its buffers.  If you can modify the
program, you should have it use setbuf() to turn off buffering of output.
If not, you can use Expect to have its output go through a pseudo-tty, so
that the output will be flushed automatically after every line (Expect
comes with a pre-written script that does this).

-- 
Barry Margolin, barmar@genuity.net
Genuity, Woburn, MA
*** DON'T SEND TECHNICAL QUESTIONS DIRECTLY TO ME, post them to newsgroups.
Please DON'T copy followups to me -- I'll assume it wasn't posted to the group.
 

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