x += y
This performs a fetch-and-add operation. The atomic integer x is increased by y and its original value is returned. This operation occurs atomically and is thread safe.
i1 : x = new AtomicInt from 12 o1 = 12 o1 : AtomicInt
i2 : x += 10 o2 = 12
i3 : x o3 = 22 o3 : AtomicInt