Experimental Physics and
Industrial Control System

Zenon Szalata <[email protected]> · Fri, 22 Aug 2014 22:08:54 -0700

I am sending this to a wider audience hoping to improve chances for a 
useful suggestion on how to proceed solving this problem.
Here is a description of the problem:
My epicsQT application at times fails to come up properly.  Each time it 
fails, attaching a debugger reveals that it is a waiting on a mutex, 
which it never gets, so it hangs forever.  An example of a traceback is 
attached.  It does not get stuck in the same place each time it 
happens.  It always involves ca_clear_channel routine.

The affected application is fairly large.  There are more than 500 EPICS 
aware widgets.  The application gets stuck usually after about 250 
channel access connections are made.  Sometimes it happens much sooner 
and sometimes it makes it all the way.  The application is coded such 
that in the main window there are number of nested tabbed widgets.

Since most of the time the problem seems to occur after a substantial 
number of CA connections are made, I decided to create a variant of this 
application.  The new variant consists of a main window with a number of 
push buttons each designed to launch a dialog.  The class object is 
created when the dialog is launched. Each of these dialog windows 
contains the widgets from each page of the tabbed widgets of the 
original application.  This way, each dialog contains  a modest number 
of CA aware widgets.  I have implemented signals and slots such that 
when a dialog is dismissed, a signal is emitted which the main window 
intercepts and destroys the dialog objects.  The end result is that this 
application can be always started and hang only when number of these 
dialog windows are popped up or put it differently, when there are a 
large number of active CA connection in this application and a new 
dialog is popped up.

I have not spent much time reading the epicsQT code so I don't really 
know why it is doing what it is doing.  I can't tell if the fault is in 
the epicsQT implementation or is it perhaps some resource depletion 
issue.  I hope for some suggestion as to how to proceed diagnosing this.

EPICS version is 3.14.12.4
epicsQT is 2.8.1
qt is 4.8.5
The computer is RHEL6 64 bits with quad core Xeon W3550, 6GB memory.

Thank you in advance,
Zen

Experimental Physics and Industrial Control System

Experimental Physics and
Industrial Control System