src/Pure/PIDE/session.scala

 
 package isabelle
 
 
 import scala.collection.immutable.Queue
+import scala.annotation.tailrec
 
 
 object Session
 {
   /* outlets */

 
   def snapshot(name: Document.Node.Name = Document.Node.Name.empty,
       pending_edits: List[Text.Edit] = Nil): Document.Snapshot =
     global_state.value.snapshot(name, pending_edits)
 
+  @tailrec final def await_stable_snapshot(): Document.Snapshot =
+  {
+    val snapshot = this.snapshot()
+    if (snapshot.is_outdated) {
+      Thread.sleep(output_delay.ms)
+      await_stable_snapshot()
+    }
+    else snapshot
+  }
+
   def start(start_prover: Prover.Receiver => Prover)
   {
     file_formats
     _phase.change(
       {