I have two processes and one queue. First item is already picked from the queue by one process but it is not completed or in exception. Can we directly pick second item from the queue by another process? What is going to happen to the first item. Will it be in exception.
Queue items which has a lock on it is in process of being made. If a new process or the same process runs 'Get Next Item' again then you will lock next item. First item will continue being locked and only on marking item complete or failed or crashing process then this item will get a new status.
You can test this easily by populating your queue with 5 items, then run 'Get Next item', then run 'Get Next item' again in same process. Then you will now have two locked items. When you reset your run BP will set both item to failed as they never got a new status before you crashed/restarted your process.
It's generally not a good idea to use same queue for different processes. If you use same process to run it multiple times then it's absolutely acceptable, but then you need to be sure all actions are thread safe. Example on an thread error, two processes can't write to same file at the same time.