/**
 * 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 }

}

/**
 * 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 }

}