[Pythonmac-SIG] Warning: The process has forked and you cannot use this CoreFoundation functionality safely.

[Russell E. Owen]

I maintain a RO.DS9, a cross-platform Python module that controls ds9 
(a.k.a. SAOImage DS9), an astronomical image viewer.

The module starts by launching ds9 with a window of a known name (this 
is required to further command it), and that's where I run into trouble 
on MacOS X.

On unix and Windows ds9 is an executable that I run using 
subprocess.Open and provide the necessary command-line arguments to set 
the window name. That works fine.

On MacOS X I used to do the same thing. The application is a bundle 
"SAOImage DS9.app" that contains the executable ds9 that takes the same 
command-line arguments. Running ds9 still works on Leopard, but results 
in the nasty warning:

The process has forked and you cannot use this CoreFoundation 
functionality safely. You MUST exec().

>From a google search, I found this:
-------
This is caused by programs that use the fork() or daemon() function in 
combination with higher-level APIs. In Leopard you cannot use the 
CoreFoundation (CF...) APIs on the child side of a fork() without 
following it with an exec*() function. This has always been true, but 
Leopard is much more stingy about this kind of thing.

So clearly I should not be doing this. But what to do instead?

The simplest, but inadequate, alternative is to use subprocess to run 
the command "open -a SAOImage DS9". This works but I can't send 
command-line arguments, so I can't control the name of the window, which 
cripples the module.

Is there some Mac-safe way to start the ds9 command-line application 
from my python module? I don't really know what it means to "run an 
exec*() function after a fork" and didn't think I was forking anything 
anyway -- I'm trying to start an independent process. I fear that the 
fork may be in ds9 itself and that there's nothing I can do, but I hope 
I'm wrong.

-- Russell