inline fun <K, V> ConcurrentMap<K, V>.getOrPut(
defaultValue: () -> V
Concurrent getOrPut, that is safe for concurrent maps.
Returns the value for the given key. If the key is not found in the map, calls the defaultValue function, puts its result into the map under the given key and returns it.
This method guarantees not to put the value into the map if the key is already there, but the defaultValue function may be invoked even if the key is already in the map.