Make programme single-instance only. Fix #65

[lx223]

The change highlights look more confusing than the changes themselves.

What I have done is:

• added a mutex object with a GUID name
• used its waitone method to detect already-running instance and exit programme if another instance is already running

[garethed]

Thanks. This looks promising, but I don't think you're handling all the edge cases. See e.g. http://stackoverflow.com/questions/229565/what-is-a-good-pattern-for-using-a-global-mutex-in-c/229567 for a quite detailed example - in particular you're not cleaning up after your mutex or handling AbandonedMutexExceptions properly.

A couple of other ways this could be nicer:

• wrap it in a descriptive function name so it's clear what's happening
• rather than increasing the indentation level of the whole method, test for the bad case and bail out early

i.e. OnStartup should look like;

if (AnotherInstanceIsRunning()) {
  // shutdown
}

// (otherwise) do all the existing stuff

and all your new code should be in a new AnotherInstanceIsRunning method

[lx223]

Thanks for the comment and sry for the mess in the first commit. Hopefully, this looks better now.