src/Pure/Concurrent/volatile.scala

--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/src/Pure/Concurrent/volatile.scala	Sat Aug 28 17:20:53 2010 +0200
@@ -0,0 +1,22 @@
+/*  Title:      Pure/Concurrent/volatile.scala
+    Author:     Makarius
+
+Volatile variables.
+*/
+
+package isabelle
+
+
+class Volatile[A](init: A)
+{
+  @volatile private var state: A = init
+  def peek(): A = state
+  def change(f: A => A) { state = f(state) }
+  def change_yield[B](f: A => (B, A)): B =
+  {
+    val (result, new_state) = f(state)
+    state = new_state
+    result
+  }
+}
+