#1300 qt terminal crash when left-clicking in plot

[Markus Appel]

I have the current dev configured --with-qt and built with libqt4 (4:4.8.1-0ubuntu4.4) on Ubuntu 12.04.

When I plot something and start left-clicking around in the plot, the qt terminal closes and shows the error message below in the terminal. This happens sometimes after 2 clicks, sometimes only after >10.

Terminal type set to 'qt'

gnuplot> plot sin(x)
gnuplot> ############### WRONG readEvent 758197814 69
Qt terminal communication error: select() error 9 Bad file descriptor

gnuplot> plot sin(x)
Could not connect gnuplot_qt "" . Starting a new one
gnuplot> ############### WRONG readEvent 758132277 69
Qt terminal communication error: select() error 9 Bad file descriptor

gnuplot>

A build of gnuplot 4.6.4 with qt on the same system does not show this bug.

[Ethan Merritt]

The usual cause for that error message is a mismatch between the version of gnuplot itself and the version of the gnuplot_qt outboard driver. If you had a previous version of gnuplot installed and now you've just built but not installed a new one, it could be failing because it still tries to use the newly built gnuplot but the old gnuplot_qt. Try setting environmental variable GNUPLOT_DRIVER_DIR to the directly containing your newly built version.

[Markus Appel]

Thanks for your quick response.
I indeed ran gnuplot from the build tree. But now I uninstalled all existing versions of gnuplot, manually removed all /usr/local/libexec/gnuplot/*/gnuplot_qt binaries, installed a newly built version, and the problem persists. I set GNUPLOT_DRIVER_DIR=/usr/local/libexec/gnuplot/4.7 (which was created after installation) but that did not resolve my problem. Neither when I set the variable to my build directory.

I tried setting the variable deliberately to the binary from a 4.6.4 build, in that case a similar error happens immediately when I try to plot something.

[Ethan Merritt]

Yes, I can now confirm the problem.
I don't know what's going on, but it appears to have been introduced with the dynamic initialization of the qt terminal data structures.
If we can't figure out what the problem is, I may have to revert that.

[Ethan Merritt]

It turns out the regression came in the patch subsequent to the dynamic initialization patch. I've reverted the code to essentially what it was before that. I think that it is still possible to trigger this error, but it is far harder to hit than in the now-reverted code.

[Markus Appel]

Thanks, I tested it briefly, the error doesn't occur as easily any more.