src/Pure/Concurrent/volatile.scala

discontinued "isabelle usedir" option -r (reset session path);
simplified internal session identification: chapter / name;
clarified chapter index (of sessions) vs. session index (of theories);
discontinued "up" links, for improved modularity also wrt. partial browser_info (users can use "back" within the browser);
removed obsolete session parent_path;

/*  Title:      Pure/Concurrent/volatile.scala
    Module:     PIDE
    Author:     Makarius

Volatile variables.
*/

package isabelle


object Volatile
{
  def apply[A](init: A): Volatile[A] = new Volatile(init)
}


final class Volatile[A] private(init: A)
{
  @volatile private var state: A = init
  def apply(): A = state
  def >> (f: A => A) { state = f(state) }
  def >>>[B] (f: A => (B, A)): B =
  {
    val (result, new_state) = f(state)
    state = new_state
    result
  }
}