what is the difference between ConcurrentMap getOr...

# stdlib

[christophsturm]

what is the difference between ConcurrentMap getOrPut and computeIfAbsent?

[enleur]

computeIfAbsent does not work with nulls

[enleur]

mutableMapOf<String, Int?>().apply {
    getOrPut("b") { null}
} // {b=null}

mutableMapOf<String, Int?>().apply {
    computeIfAbsent("b") { null}
} // {}

[dmitriy.novozhilov]

/**
 * 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.
 */
public inline fun <K, V> ConcurrentMap<K, V>.getOrPut(key: K, defaultValue: () -> V): V {
    // Do not use computeIfAbsent on JVM8 as it would change locking behavior
    return this.get(key)
            ?: defaultValue().let { default -> this.putIfAbsent(key, default) ?: default }

}

[christophsturm]

@dmitriy.novozhilov actually i did read the kdoc and wondered why it does not explain whats different from computeIfAbsent

[dmitriy.novozhilov]

ConcurrentHashMap.putIfAbsent takes a lock even if map contains key. So getOrPut provides a fastpath without taking that lock