Re: gnuplot and DISPLAY

[Daniel J S. <dan...@ie...>]

Daniel J Sebald wrote:
> Ethan A Merritt wrote:
> 
>>On Thursday 08 March 2007 21:59, Daniel J Sebald wrote:
>>
>>
>>>Oh yeah, I see now.  That isn't the same error message as 
>>>when gnuplot can't find gnuplot_x11.  gnuplot_x11 is the one having 
>>>problems opening the X display.  Is there some way for Allin to 
>>>confirm that the version of gnuplot_x11 for 4.2 was installed properly 
>>>and it is not the 4.0 version of gnuplot_x11?    
>>
>>
>>Doesn't matter.  No matter how badly gnuplot_x11 dies, it shouldn't
>>do more than generate an error message on the gnuplot end.
>>Apparently that's not the case, but I haven't yet understood the
>>failure path.
> 
> 
> Yeah, that's right.  Well, there are a number of conditional compiles in X11_init() that would explain that behavior.  There appears to be only one "graceful" exit out of gnuplot from that point:
> 
> 
> 	if (fork() == 0) {
> 	    /* child */
> [snip]
> 	    fprintf(stderr,"Expected X11 driver: %s\n",X11_full_command_path);
> 	    perror("Exec failed");
> 	    fprintf(stderr,"See 'help x11' for more details\n");
> 	    exit(EXIT_FAILURE);
> 	}
> 
> But that set group of error messages isn't appearing in Allin's strace.
> 
> Might it be that fork() is coming back nozero and gnuplot attempts sending through the pipe and the OS doesn't like that so kills the process?

Yes, I think it is something along that line.  The only difference between 4.0 and 4.2 is the addition of the following at the end of X11_init():

#if defined(WITH_IMAGE) || defined(BINARY_X11_POLYGON)
    X11_send_endianess();
#endif

which sends a few characters through the pipe.  This code probably shouldn't be run unless there is a valid pipe.

Probably on your system Ethan and mine this is handled more gracefully.

Allin, please try the following patch and rebuild gnuplot to see if this fixes matters.

Dan