Re: Interrupts and communication with external gnuplot drivers

[<tim...@lp...>]

Ethan A Merritt a écrit :
> On Saturday 22 December 2007 13:41, Timothée Lecomte wrote:
>   
>> When the user hits ctrl-c, the SIGINT handler is supposed to be run 
>> immediately, interrupting any operation running at that time. So I would 
>> have expected communication errors because fprintf()'s used in x11.trm 
>> can be interrupted before they finish, but I don't see any such error.
>>     
>
> Two answers:
>
> Each write into the pipe from gnuplot to gnuplot_x11 is a unit.
> If you interrupt the process before it is sent, then nothing is sent.
> If you interrupt during/after it is sent, then so far as I know the
> entire write completes.  I don't think you can cause a partial write
> to a pipe by sending a signal to the task that does the writing.
>
>   
It's what my tests tend to prove, but nowhere in the docs it is said to 
behave that way. On the contrary, 'man 2 read' and 'man 2 write' 
explicitly say that a read or a write can be interrupted by a signal and 
then they won't have written or read all the bytes.

> You might be worried that the plot itself is incomplete, even though
> the individual write operations complete normally. But this doesn't matter.
> There is an explicit end-of-plot command sent over the pipe consisting
> of the single character 'E'. This is sent by X11_text().
> Until it receives that 'E', gnuplot_x11 just accummulates commands
> into a new plot structure.  If the 'E' is not received, then it will
> never try to display the plot. So it doesn't matter that it is incomplete.
>
> 	Ethan
>   
That part I don't understand too. In practice, when doing 'set samples 
10000; set isosamples 10000; splot x**2*y**2 with pm3d;' and 
interrupting the process with ctrl-c, I sometime got a partly rendered 
plot, whereas the 'E' obviously wasn't sent yet. I'm lost.

Best regards,

Timothée Lecomte