Avoid concurrent updates from RA if it is having start form

Must the form be in the start node?  I'm sure there are better ideas, but the first thing that pops into my mind is:

Have a lock flag in the record.  Check it as the first thing you do in the process, and if it's not locked, lock it, and then proceed with the process. 

Hey james. Thanks for the suggestion. But am not sure if we could use lock mechanism when action begins with start form.

Your best approach is to use some kind of pessimistic locking. This is a pretty common topic of discussion in the community, I'd recommend starting with this post for some more information: community.appian.com/.../72806

I have seen this discussion. But in my case am not triggering any process(since am using start form) to use locking mechanism. Please correct me if am wrong.

You won't be able to use a start form in this scenario as you'll have to have a script task run before hand.

If you truly must...

It's probably not a good idea, but I know you can use a!writeRecords from an interface.  You have to kick it off in an a!saveInto, though so you can't do it on load.

You could give the user a BFB (Big Friendly Button), so that they could lock it themselves.

Just an option...

Good option. But we have no control when user clicks cross mark which appears in start form by default. 

Nothing can technically prevent two users from loading the start form at the same time.  You could, however, prevent a second user from completing a start form.

But I more agree with the others here who suggest just not using a start form.