I have a scenario where a approval task is "assigned" to a department group ( say 20 people) and i need to allow a single staff to "take" or "accept" the task and work on it. during that time, other staff members may see it but cannot work on / or change it. 

ideally i need to functional way for a person "to claim/take/accept" an item. if a other person attempts to claim/take/accept" during that time, they will be unable to and should get an error message/warning message.

i have read thru the site QA and dont see easy way to do this. i see some article about an activity and then something about Performer of Previous Activity. all good an great BUT whats the experience of taking/getting the task in the first place. it should be cleaner than saying i will take an approval task and immediately complete it to "get it" and enable get next task assignment in the same UX/approval form

What isn't task accept/claim/get and release/reject task a functional feature to handle concurrent access to such tasks?

this is important requirement.