Using getOrElseUpdate of TrieMap in Scala

Question

I am using the getOrElseUpdate method of scala.collection.concurrent.TrieMap (from 2.11.6)

 // simplified for clarity

 val trie = new TrieMap[Int, Future[String]]

 def foo(): String = ... // a very long process

 val fut: Future[String] = trie.getOrElseUpdate(id, Future(foo()))

As I understand, if I invoke the getOrElseUpdate in multiple threads without any synchronization the foo is invoked just once.

Is it correct ?

Answer 1

The current implementation is that it will be invoked zero or one times. It may be invoked without the result being inserted, however. (This is standard behavior for CAS-based maps as opposed to ones that use synchronized.)