Re: gnuplot fails in background.

[Thomas S. <t.s...@fz...>]

without '&' the c-program waits for gnuplot to terminate and then
goes on. so it is guaranteed that gnuplot did its job when the
c-program finishes.
with '&' the c-program starts gnuplot without waiting and goes
on directly.
so it may happen that the c-program has finished while the gnuplot
process is still running in background or waits to get some cpu time.


Plotter-2 wrote:
> 
> Hi,
> 
> I'm not really sure this is a gnuplot problem , I'm having trouble 
> seeing where the problem lies.
> 
> I have a cgi responder written in C that works fine when running gnuplot 
> directly but if I add "&" to the command sting it fails.
> 
> I have both post.cgi and test.gnu in my cgi directory , it is called by 
> lighttpd in response to a FORM post method.
> 
> within post.c :
> 
> system("gnuplot test.gnu" );
> OK.
> system("gnuplot test.gnu &" );
> Fails to produce output but the call returns zero since it apparently 
> succeeds in creating the gnuplot process and backgrounding it before 
> gnuplot  fails.
> 
> It looks like a permissions problem or file path but testing from 
> command line it works and not backgrounding the process works for the cgi.
> 
> First line in test.gnu fails to create the file:
> system("touch /www/apache/htdocs/gnuplot.ran");
> 
> Equally , calling gnuplot with the full path of the .gnu file also fails.
> 
> Why is gnuplot failing when I detach the process?
> 
> TIA.
> 
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