[Dev] Preventing user from running multiple instances

[Andi Vajda]

> For various reasons we don't want the user to be able to run multiple 
> instances of Chandler against the same repository.  For example, if you fire 
> up two instances at the same time, one of them will complain that //Schema 
> already exists, and there are other places where things don't quite work.  So 
> I was wondering if anyone had an idea for a cross-platform way to prevent 
> multiple concurrent instances accessing a repository.  Chandler could look 
> for and create a lock file next to the repository directory, and place its 
> process ID in there, thereby allowing it to detect whether an existing lock 
> file is obsolete because a previous instance died without removing it.  (Does 
> Windows have the notion of PID?)  This method leaves the repository itself 
> out of it -- purely an application level function.  Or we could get the 
> repository involved and have it keep track of which process has it open, and 
> the application layer asks the repository.  I guess I would lean toward the 
> former method.
>
> I'm sure there must be some python module that does this already, in a 
> cross-platform way...

This is an old problem that I fixed a few months ago. If you don't want 
multiple Chandlers to run concurrently, start the first one with 
-x or --exclusive.

Andi..

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