[Starkit] corruption of starkits by double access

[Jean-Claude Wippler]

Steve Landers wrote:

> Steve Blinkhorn wrote:
>
>> How can I prevent write-enabled starkits from being corrupted by  
>> being
>> accessed a second time whilst already being accessed?   We are seeing
>> this as an occasional problem on Windows, where a user "loses" an  
>> open
>> window behind another application, and blithely double-clicks again.
>>
>> We can't find what sort of corruption is going on, because the  
>> starkit
>> then will not unwrap.
>
> This is a topic I'm also very interested in - for the very same  
> reasons.
>
> From the reading I've done on the topic, cross-platform locking  
> seems to be a minefield (or perhaps a cesspit - depending on your  
> point of view).
>
> I'm wondering if the 80/20 solution might be to create a small  
> Critcl extension that tries to create a Windows exclusive advisory  
> lock on the kit / metakit file?
>
> Does anyone have an opinion on whether this is an approach worth  
> investigating further?

There's a page on this on the wiki - http://wiki.tcl.tk/593

But if you drop x-platform, i.e. a plain Windows solution, then it's  
probably all quite easy to solve.  A lockfile opened in exclusive  
mode, or opening a socket on a fixed port number (which one is the  
big Q!), or perhaps actually solve the *real* problem: when launched  
again, look for another instance and bring it to the front / exit if  
it exists.  Much friendlier than exiting with some error.  Can a top- 
level window be found by name on Windows?  I don't remember.  With  
Critcl, I would think that it should be possible to do this in the  
same way as non-Tcl single-launch Windows apps do it.  DDE can also  
be used for this IIRC, you can probably find more good info on these  
approaches with Google.

-jcw