Corrected scheduling policy unfairness that affects stop ordering

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

@@ -62,7 +62,19 @@ public void register(ISchedulableThread thread, long priority)
 	{
 		synchronized (threads)
 		{
-			threads.add(thread);
+			// The last thread is the one currently running, so insert ahead of this
+			// one so that the new thread is scheduled before the current one is
+			// next scheduled.
+			int count = threads.size();
+
+			if (count == 0)
+			{
+				threads.add(thread);
+			}
+			else
+			{
+				threads.add(count - 1, thread);
+			}
 		}
 	}
 

core/vdmj/src/test/resources/Overture/evaluate/stoptest.vpp

@@ -2,6 +2,7 @@ system SYS
 instance variables
 	static public obj1 : A := new A();
 	static public obj2 : A := new A();
+	static public obj3 : A := new A();
 
 	cpu1:CPU := new CPU(<FP>, 1E6);
 	cpu2:CPU := new CPU(<FP>, 1E6);
@@ -14,6 +15,7 @@ operations
 	(
 		cpu1.deploy(obj1, "Test object one");
 		cpu2.deploy(obj2, "Test object two");
+		cpu2.deploy(obj3, "Test object three");
 	)
 
 end SYS
@@ -53,17 +55,17 @@ operations
 	test() ==
 	(
 		SYS`obj1.run();
-		SYS`obj1.null();
 		SYS`obj1.kill();
 
-		SYS`obj1.run();
-		SYS`obj2.null();
-		SYS`obj2.kill(SYS`obj1);
+--		SYS`obj1.run();
+--		SYS`obj2.null();
+--		SYS`obj2.kill(SYS`obj1);	-- Error, wrong CPU
 
 		SYS`obj1.run();
 		SYS`obj2.run();
-		SYS`obj2.null();
-		SYS`obj2.kill({SYS`obj1, SYS`obj2});
+		SYS`obj3.run();
+		SYS`obj2.kill({SYS`obj2, SYS`obj3});
+		SYS`obj1.kill(SYS`obj1);
 	)
 
 end Test