Experimental Physics and Industrial Control System
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Back in January I described a problem we have been having with EDM ever
since we moved from HP-UX to RedHat Enterprise Linux in 2006. It was
serious enough to prevent us from completing our Linux deployments in
some areas. With help from John this has now been resolved.
The problem was that operators would sometimes find at random times that
their EDM displays were showing old data that didn't match displays on
other workstations. In fact, the EDM screens were completely frozen with
no graphical updates. Opening or closing a display would always resolve
the problem, but for a long time we couldn't reproduce it deliberately.
To help us diagnose the problem, John added an option in EDM 1-11-1zm
that allows you to set an environment variable EDMIGNOREICONIC that
causes EDM to ignore the iconified state of windows. That is, with the
variable set, all widgets get updated even if the window manager reports
that the window is iconified. This made our frozen screen problem go
away and pointed me to the source of the problem. There is a bug in the
code that checks windows for their iconified state.
Using EDM 1-11-1zm or later with EDMIGNOREICONIC avoids the problem. I
have sent John a patch for his review that corrects the bug and
eliminates the need for setting EDMIGNOREICONIC.
To see the bug in action (or lack thereof) you need to open a number of
EDM displays that is a multiple of 11. Make sure that at least one
display is on a different desktop workspace (which is equivalent to
being iconified under many window managers). Once the 11th display is
open, switch workspaces and you will find that any displays that were on
other workspaces are now frozen. Opening or closing a display will
unfreeze all the displays (since the total is no longer 11). Note that
when counting the open displays, embedded displays count separately. So,
for example, a single EDM window that contains 3 embedded displays will
count as 4 displays total. We have observed this on RHEL 3, 4, and 5
using GNOME or KDE. There are also reports of it on Scientific Linux and
Debian. We did not see the problem using CDE on HP-UX probably due to
different window/workspace handling.
My hearty thanks to John for helping us track this down and to all of
the operators here who diligently reported the problem with enough
detail to finally nail it.
--Brian
--
Brian S. Bevins, PE
Computer Scientist / Mechanical Engineer
Thomas Jefferson National Accelerator Facility
"Nothing in all the world is more dangerous than
sincere ignorance and conscientious stupidity."
--Martin Luther King Jr.
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ANJ, 31 Jan 2014 |
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