Experimental Physics and
Industrial Control System

Andrew Johnson <[email protected]> · Fri, 23 May 2008 14:49:12 -0500

Hi Artem,

Artem Kazakov wrote:

I recall that you've showed me that on some of the machines my ruby
script was waiting for the output from the caputackt command, while
the latter being zombie.
So yesterday encountered the same behavior on my Mac-box. And the
funny thing is that if I start caRepeater as separate independent
process, everything works as supposed.
But if the caRepeater is not running, then it is started somewhere
from ca library (I guess?) and then there is a zombie walking around
and caRepeater process is still running.
If I kill that spawned caRepeater process by hand, than zombie finally
dies and script continues until next caLib using command (such as
caput) and then again there is a zombie and caRepeater.
Is it supposed to be like that ?
I'm not so familiar with the ca lib internals and caRepeater
interaction, but may be you can get give me a hint on what's going on?

If there is no caRepeater running on the machine, a CA client program

will start one when it initializes the CA library. The preferred method

is to fork() and execlp() the external caRepeater program, but if it

can't find caRepeater in $PATH the child process will print a warning

and run the repeater functionality itself. Do you have a copy of

caRepeater in your $PATH? I suspect not, and that if you did you'd find

the zombie would not appear — please confirm that if possible.

What are the parent processes of the caRepeater and of the zombie?

However just copying caRepeater into your $PATH won't resolve the

fundamental issue that somehow it's generating zombies. I'm not sure

how, but it obviously can. I double-checked the src/libCom/osi/os/posix

code that makes the fork()/execlp() calls; it is not getting the child

and parent processes mixed up.

- Andrew
--
Talk is cheap. Show me the code. -- Linus Torvalds

Experimental Physics and Industrial Control System

Experimental Physics and
Industrial Control System