[Starkit] corruption of starkits by double access

[Steve Blinkhorn]

 > 
 > > A lockfile opened in exclusive mode, or opening a socket on a fixed  
 > > port number (which one is the big Q!),
 > 
 > A lockfile has two problems - one is the extra file which (in some  
 > circumstances) is not ideal.
 > 

Lockfiles sound nice and simple, but if, for some reason, an
application crashes and the lockfile is left in place you have created
a user support problem.

 > 
 > A port number has the problem that it might trigger the windows  
 > firewall (no big deal, but could surprise end-users and require  
 > documentation).
 > 

Thanks for that warning - firewalls and proxies are the source of many
unwelcome surprises.   Our "users" are mostly one-trip even when our
customer isn't.

 > > or perhaps actually solve the *real* problem: when launched again,  
 > > look for another instance and bring it to the front / exit if it  
 > > exists.
 > 
 > The situation I need to cope with isn't restricted to one user  
 > unfortunately. Steve's situation might be different.
 > 
 > > Much friendlier than exiting with some error.  Can a top-level  
 > > window be found by name on Windows?
 > 
 > Yes - TWAPI does it. Ffidl almost certainly will let you.  I'm not  
 > sure this approach guarantees uniqueness although I suspect you'd get  
 > a close approximation ;-)
 > 

Much the nicest solution in principle.   The problem I see is the
overhead: TWAPI is nearly half a megabyte compressed.   That would add
an extra 50% to our download.   Does anyone know off-hand, i.e.
without delving into the TWAPI sources or going off to a Microsoft
site for the documentation, whether finding a window by name is just a
call to a dll function?   That would be much more lightweight, if
fiddly.

One thing I *thought* might be raised would be the limitation of
Metakit files to only one client for writing.   I half-expected
someone to point to a non-fatal error that might be raised if a second
client attempted to write to it, and using an error trap as a
detection mechanism with a graceful exit.   But I am underinformed
about these things.

--
Steve Blinkhorn <steve at prd.co.uk>