jboner/akka — comment on commit e60d3f386d0239c12c7dccdc794b484402c2b1cc
File: akka-actor/src/main/scala/akka/actor/ActorSystem.scala line 405
By viktorklang:

putIfAbsent with key and a CountDownLatch(1), if successful, init the extension and do a conditional replace of the latch and the extension, count down the latch, profit