computeIfAbsent called from inside its own mapping function (single thread)
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HashMap, inner key in a different bin:                    threw java.util.ConcurrentModificationException
ConcurrentHashMap, inner key in a different bin:          no exception, size=2
ConcurrentHashMap, inner key, same bin (bin was empty):   threw java.lang.IllegalStateException: Recursive update
ConcurrentHashMap, inner key, same bin (bin had a node):  threw java.lang.IllegalStateException: Recursive update