Shared list support.
Unstable API.
SharedList[A] = object head, tail: SharedListNode[A] lock*: Lock
proc add[A](x: var SharedList[A]; y: A)
proc clear[A](t: var SharedList[A])
proc deinitSharedList[A](t: var SharedList[A])
proc init[A](t: var SharedList[A])
proc iterAndMutate[A](x: var SharedList[A]; action: proc (x: A): bool)
iterator items[A](x: var SharedList[A]): A