ConcurrentHashMap's iterator is weakly consistent: it never throws CME
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map before: {0=v0, 1=v1, 2=v2, 3=v3, 4=v4}
entries visited during iteration (original 5, plus possibly some newly-added ones): 19
map after: 24 entries total
ConcurrentModificationException thrown: false
(weakly consistent: may or may not reflect the mutation, but is guaranteed never to throw)