Correction for two successive stop calls

core/vdmj/src/main/java/org/overturetool/vdmj/scheduler/ISchedulableThread.java

@@ -57,7 +57,7 @@ public interface ISchedulableThread
 
 	public abstract void suspendOthers();
 
-	public abstract void stopThread();
+	public abstract boolean stopThread();
 
 	public abstract void reschedule(Context ctxt, LexLocation location);
 

core/vdmj/src/main/java/org/overturetool/vdmj/scheduler/InitThread.java

@@ -200,7 +200,7 @@ public void clearAlarm()
 		throw new NotSupportedError();
 	}
 
-	public void stopThread()
+	public boolean stopThread()
 	{
 		throw new NotSupportedError();
 	}

core/vdmj/src/main/java/org/overturetool/vdmj/scheduler/SchedulablePoolThread.java

@@ -431,14 +431,23 @@ public static void signalAll(Signal sig)
 		BasicSchedulableThread.signalAll(sig);
 	}
 
-	public synchronized void stopThread()
+	public synchronized boolean stopThread()
 	{
-		stopCalled = true;
-		timestep = Long.MAX_VALUE;			// Don't take part in time step
-
-		if (Thread.currentThread() != this.getThread())
+		if (!stopCalled)
+		{
+			stopCalled = true;
+			timestep = Long.MAX_VALUE;			// Don't take part in time step
+
+			if (Thread.currentThread() != this.getThread())
+			{
+				setState(RunState.RUNNABLE);	// So that thread is rescheduled
+			}
+
+			return true;
+		}
+		else
 		{
-			setState(RunState.RUNNABLE);	// So that thread is rescheduled
+			return false;
 		}
 	}
 

core/vdmj/src/main/java/org/overturetool/vdmj/statements/StopStatement.java

@@ -145,8 +145,10 @@ private void stop(ObjectValue target, Context ctxt) throws ValueException
 		{
 			if (th instanceof ObjectThread || th instanceof PeriodicThread)
 			{
-				th.stopThread();	// This may stop current thread at next reschedule
-				count++;
+				if (th.stopThread())	// This may stop current thread at next reschedule
+				{
+					count++;
+				}
 			}
 		}