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Inhibiting duplicate apps in Windows?

Peter Hansen peter at engcorp.com
Thu Jun 20 21:39:56 EDT 2002 
Chris Liechti wrote:
> 
> "Edward K. Ream" <edream at tds.net> wrote in news:3D11F9E8.DFFFC8E4 at tds.net:
> > What I would like is for the second copy of Leo to detect that another
> > copy of leo.py is already running, send a message to the first copy and
> > then exit. I wonder if anyone knows how this might be done?

> dumb solution: create a "lock file" and remove it on programm exit. the
> other problem is that you have to delete it manually when the app crashes
> (i deleted may lock files with older Netscapes ;-)

I wonder whether there's not a simple way to avoid manual deletion.
If one application creates the lock file, it can hold it open as 
long as it is running.  A second invocation can detect the first
by its failure to open the same file for writing.  If the file
already exists, it can try to delete it with os.remove(). That
should fail if the first application still has it open, but if 
the first application actually crashed, the OS should allow the
file to be removed, at which point the new invocation can safely
recreate it, knowing it now has the lock.

Haven't actually tried this myself... :)

-Peter
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