We adapt a variant of permission-accounting separation logic to a concurrent Java-like language with fork/join. To support both concurrent reads and information hiding, we combine fractional permissions with abstract predicates. We present a separation logic contract for iterators that prevents data races and concurrent modifications. Our program logic is presented in an algorithmic style, based on a proof-theoretical logical consequence. We show that verified programs satisfy the following properties: data race freedom, absence of null-dereferences and partial correctness.