Prevent more than one instance of task running at the same time

[gurpreetg]

I am wondering if it's possible to obtain a behaviour in v1 so a task is not ran if it's already running. For example, if request 1 pushes taskX and request2 pushes taskX only a second later, assuming taskX pushed by request 1 is still running, can we ensure that taskX pushed by request2 will be skipped.