diff --git a/plugins/pyloader/src/builtin-policies/rr_priority.py b/plugins/pyloader/src/builtin-policies/rr_priority.py
index ab1413b..9365fb1 100644
--- a/plugins/pyloader/src/builtin-policies/rr_priority.py
+++ b/plugins/pyloader/src/builtin-policies/rr_priority.py
@@ -58,3 +58,16 @@ the time slice will have to end before the former can run."""
         self.sort(queue,by_ltime)
         self.sort(queue,by_prio)
 
+        # manage preemption: see if we've a running thread
+        # in the ready queue, and if it can still run
+        if self.is_preemptive() == True:
+            higher_prio = queue.get_item_at(0).get_current_priority()
+            i = 0
+            while i < queue.size():
+                sched = queue.get_item_at(i)
+                priority = sched.get_current_priority()
+                if(priority != higher_prio):
+                    break
+                if sched.get_state() == "running":
+                    queue.bubble_to_front(i)
+                i += 1
diff --git a/plugins/pyloader/src/builtin-policies/sjf.py b/plugins/pyloader/src/builtin-policies/sjf.py
index b9e8a68..45bb5f8 100644
--- a/plugins/pyloader/src/builtin-policies/sjf.py
+++ b/plugins/pyloader/src/builtin-policies/sjf.py
@@ -53,3 +53,4 @@ Time Next in this case."""
             a.get_total_cpu_time() - a.get_elapsed_time() < \
             b.get_total_cpu_time() - b.get_elapsed_time()
         self.sort(queue,cmpf)
+        
diff --git a/plugins/pyloader/src/sgpem.i b/plugins/pyloader/src/sgpem.i
index 199a04c..01ec084 100644
--- a/plugins/pyloader/src/sgpem.i
+++ b/plugins/pyloader/src/sgpem.i
@@ -150,15 +150,6 @@ namespace sgpem {
 	public:
 		virtual ~Schedulable() = 0;
 		
-		enum state
-			{
-				state_running    = 1<<0,
-				state_ready      = 1<<1,
-				state_blocked    = 1<<2,
-				state_future     = 1<<3,
-				state_terminated = 1<<4
-			};
-	
 		virtual unsigned int  get_arrival_time() const = 0;
 		virtual unsigned int  get_elapsed_time() const = 0;
     virtual int           get_last_acquisition() const = 0;
@@ -166,7 +157,30 @@ namespace sgpem {
 		virtual int           get_base_priority() const = 0;
 		virtual int           get_current_priority() const = 0;
 		virtual unsigned int  get_total_cpu_time() const = 0;
-		virtual state         get_state() const = 0;
+
+    %ignore Schedulable::get_state() const;
+    %extend {
+      const char* get_state() const
+      {
+        switch(self->get_state())
+          {
+          case Schedulable::state_future:
+            return "future";
+          case Schedulable::state_terminated:
+            return "terminated";
+          case Schedulable::state_running:
+            return "running";
+          case Schedulable::state_ready:
+            return "ready";
+          case Schedulable::state_blocked:
+            return "blocked";
+          default:
+            // should never get here
+            return "undefined";
+          }
+      }
+    }
+    
 		
 		%ignore Schedulable::get_name() const;
 		%extend {
@@ -204,6 +218,7 @@ namespace sgpem {
 			sgpem::Thread& get_item_at(position index);
 			
 			void swap(position a, position b) throw(std::out_of_range);
+      void bubble_to_front(position x) throw(std::out_of_range);
 			
     private:
 			// Avoid instantiation and copy
diff --git a/src/backend/concrete_history.cc b/src/backend/concrete_history.cc
index f142cad..f628cc4 100644
--- a/src/backend/concrete_history.cc
+++ b/src/backend/concrete_history.cc
@@ -82,7 +82,7 @@ static T* deep_find(const std::vector<T*>& v, const T& obj)
 // -----------------
 
 ConcreteHistory::ConcreteHistory()
-    : History(), _snapshots()
+    : History(), _snapshots(), _sealed(false)
 {
   _snapshots.push_back(new ConcreteEnvironment());
 }
@@ -95,7 +95,7 @@ ConcreteHistory::~ConcreteHistory()
 }
 
 ConcreteHistory::ConcreteHistory(const ConcreteHistory& h) :
-    History(h)
+    History(h), _sealed(h._sealed)
 {
   typedef Snapshots::const_iterator SnapIt;
   for (SnapIt it = h._snapshots.begin(); it != h._snapshots.end(); ++it)
@@ -489,12 +489,16 @@ ConcreteHistory::edit_subrequest(SubRequest& subrequest,
 
 
 void
-ConcreteHistory::step_front(position p)
+ConcreteHistory::set_front(position p)
 {
-  _front = p;
-  if (p > _snapshots.size())
-    _front = _snapshots.size();
-  notify_change();
+  position old_front = _front;
+  if (p > _snapshots.size() - 1)
+    _front = _snapshots.size() - 1;
+  else 
+    _front = p;
+
+	if(old_front != _front)
+    notify_change();
 }
 
 void
@@ -507,6 +511,7 @@ ConcreteHistory::reset(bool notify)
   for_each(it, _snapshots.end(), deletor<ConcreteEnvironment>());
   _snapshots.resize(1); // Truncate to keep only our "model"
   _front = 0;
+  _sealed = false;
 
   if (notify)
     notify_change();
@@ -519,3 +524,18 @@ ConcreteHistory::notify_change()
   for (it = _observers.begin(); it != _observers.end(); it++)
     (*it)->update(*this);
 }
+
+
+bool
+ConcreteHistory::is_sealed() const
+{
+  return _sealed;
+}
+
+bool
+ConcreteHistory::seal()
+{
+  bool t = _sealed;
+  _sealed = true;
+  return t;
+}
diff --git a/src/backend/concrete_history.hh b/src/backend/concrete_history.hh
index 89d5574..aa24cd6 100644
--- a/src/backend/concrete_history.hh
+++ b/src/backend/concrete_history.hh
@@ -109,8 +109,13 @@ namespace sgpem
                                                resource_key_t resource_key,
                                                time_t  duration);
 
+    // sets the front to position p
+    virtual void set_front(position p);
 
-    virtual void step_front(position p);
+		bool is_sealed() const;
+
+		// (Returns if the History was sealed before this call)
+		bool seal();
 
     virtual void reset(bool notify = true);
 
@@ -123,7 +128,8 @@ namespace sgpem
   private:
     // Disable assignment, implement it only if needed
     ConcreteHistory& operator=(const ConcreteHistory& op2);
-
+	
+		bool _sealed;
   }
   ; //~ class ConcreteHistory
 
diff --git a/src/backend/concrete_simulation.cc b/src/backend/concrete_simulation.cc
index 55650cd..796a0df 100644
--- a/src/backend/concrete_simulation.cc
+++ b/src/backend/concrete_simulation.cc
@@ -64,7 +64,7 @@ ConcreteSimulation::jump_to(History::position p) throw(UserInterruptException, N
     // pauses the simulation (see below)
  		break;
   case state_stopped:
-    _history.step_front(0);
+    _history.set_front(0);
     break;
   default:
     break;
@@ -86,7 +86,7 @@ ConcreteSimulation::jump_to(History::position p) throw(UserInterruptException, N
 		yet_to_finish = step();
     increment++;
   }
-  get_history().step_front(p);
+  get_history().set_front(std::min(p, _history.get_size()));
 	if (!yet_to_finish)
 		stop();
 
@@ -126,7 +126,7 @@ ConcreteSimulation::run() throw(UserInterruptException, NullPolicyException, Mal
   switch (_state)
   {
   case state_stopped:
-    _history.step_front(0);
+    _history.set_front(0);
     break;
   default:
     break;
@@ -136,9 +136,10 @@ ConcreteSimulation::run() throw(UserInterruptException, NullPolicyException, Mal
 
   //step forward
   bool yet_to_finish = step();
-  get_history().step_front(get_history().get_front() + 1);
+  _history.set_front(_history.get_front() + 1);
   if (yet_to_finish)
     {
+
       if(_mode == mode_step_by_step) 
         pause();
       else
@@ -173,10 +174,23 @@ ConcreteSimulation::step()
   
   try
     {
-      //step forward
+      // step forward
       bool yet_to_finish = true;
-			if (get_history().get_front() == get_history().get_size() - 1)
-				yet_to_finish = Scheduler::get_instance().step_forward(_history, *get_policy(), *get_resource_policy());
+			if (_history.get_front() == _history.get_size() - 1)
+				if(!_history.is_sealed())
+					yet_to_finish = Scheduler::get_instance().step_forward(_history, *get_policy(), *get_resource_policy());
+        else 
+          yet_to_finish = false;      
+
+      if (!yet_to_finish) _history.seal();
+
+      // since the simulation expects to be notified
+      // of simulation termination when reaching the last environment
+      // and the front will be updated just out of this method,
+      // we have to make this horrible thing
+      if (_history.get_front() == _history.get_size() - 2 && _history.is_sealed())
+        yet_to_finish = false;
+     
 			return yet_to_finish;
     }
   catch (const CPUPolicyException& e)
diff --git a/src/backend/history.hh b/src/backend/history.hh
index 77a814a..5527f4e 100644
--- a/src/backend/history.hh
+++ b/src/backend/history.hh
@@ -129,6 +129,7 @@ namespace sgpem
                                         time_t  duration) = 0;
 
 		virtual position get_front() const;
+		virtual bool is_sealed() const = 0;
 
     virtual void  attach(HistoryObserver& observer);
     virtual void  detach(const HistoryObserver& observer);
diff --git a/src/backend/ready_queue.cc b/src/backend/ready_queue.cc
index eba81d6..835bbfd 100644
--- a/src/backend/ready_queue.cc
+++ b/src/backend/ready_queue.cc
@@ -27,7 +27,7 @@ using sgpem::ReadyQueue;
 
 void
 ReadyQueue::swap(position a, position b)
-throw (std::out_of_range)
+  throw (std::out_of_range)
 {
   if (a == b) return;
 
@@ -51,7 +51,7 @@ ReadyQueue::size() const
 
 sgpem::Thread&
 ReadyQueue::get_item_at(position index)
-throw (std::out_of_range)
+  throw (std::out_of_range)
 {
   // Checks index access
   return *_scheds.at(index);
@@ -59,7 +59,7 @@ throw (std::out_of_range)
 
 const sgpem::Thread&
 ReadyQueue::get_item_at(position index) const
-throw (std::out_of_range)
+  throw (std::out_of_range)
 {
   // Checks index access
   return *_scheds.at(index);
@@ -71,6 +71,18 @@ ReadyQueue::append(Thread& thread)
   _scheds.push_back(&thread);
 }
 
+
+void 
+ReadyQueue::bubble_to_front(position x)
+  throw(std::out_of_range)
+{
+  while(x > 0)
+  {
+    swap(x - 1, x);
+    --x;
+  }
+}
+
 void
 ReadyQueue::erase_first()
 {
diff --git a/src/backend/ready_queue.hh b/src/backend/ready_queue.hh
index 6c7434f..be95e17 100644
--- a/src/backend/ready_queue.hh
+++ b/src/backend/ready_queue.hh
@@ -42,6 +42,10 @@ namespace sgpem
     Thread&    get_item_at(position index) throw (std::out_of_range);
     const Thread& get_item_at(position index) const throw (std::out_of_range);
     void       append(Thread& schedulable);
+    
+		/** \brief Bubble element x to the front of the queue
+		 */
+    void       bubble_to_front(position x) throw(std::out_of_range);
     void       erase_first();
 
   private:
diff --git a/src/backend/scheduler.cc b/src/backend/scheduler.cc
index 3cf9473..b56bb48 100644
--- a/src/backend/scheduler.cc
+++ b/src/backend/scheduler.cc
@@ -61,6 +61,7 @@ typedef Environment::SubRequestQueue    SubRequestQueue;
 
 // ------------------ Static helper functions --------------
 
+inline bool is_running(const Thread* running_thread);
 static void collect_threads(const std::vector<Process*>& procs, Threads& collected_threads);
 static void prepare_ready_queue(ConcreteEnvironment& snapshot, const Threads& all_threads);
 static void terminate_all_requests_of(DynamicThread& thread, ConcreteEnvironment& environment);
@@ -75,6 +76,12 @@ static void determine_subr_allocable_status(const Resource& res, SubRequestQueue
 // ---------------------------------------------------------
 
 
+bool
+is_running(const Thread* running_thread)
+{
+  return running_thread != NULL && running_thread->get_state() == Schedulable::state_running;
+}
+
 
 // Collects all threads of an environment into a single vector
 void
@@ -480,6 +487,7 @@ Scheduler::step_forward(History& history, CPUPolicy& cpu_policy, ResourcePolicy&
               current.set_state(Schedulable::state_terminated);
               current.set_last_release(current_instant);
               terminate_all_requests_of(current, *new_snapshot);
+              running_thread = NULL;
             }
 
           // if we found the running thread, there isn't another one,
@@ -536,29 +544,31 @@ Scheduler::step_forward(History& history, CPUPolicy& cpu_policy, ResourcePolicy&
     _ready_queue = &new_snapshot->get_sorted_queue();
 
     // Determine if the policy is pre_emptive, and what time slice it uses
-    bool preemptible_policy = cpu_policy.is_pre_emptive();
+    bool preemptive_policy = cpu_policy.is_pre_emptive();
     int time_slice = cpu_policy.get_time_slice();
 
     // ?. See if old running_thread has to be put to ready state
-    // This happens when the policy makes use of preemptability by
-    // priority, or when a time slice ended
-    if (running_thread != NULL && running_thread->get_state() == Schedulable::state_running &&
-        (preemptible_policy || (time_slice > 0 && 
-                                // A process can be preempted every n-th time-slice, so we use the modulo operator
-                                (current_instant - running_thread->get_last_acquisition()) % time_slice == 0) ))
+    // This happens when a time slice ends
+    if (is_running(running_thread) && time_slice > 0 && 
+        // A process can be preempted every n-th time-slice, so we use the modulo operator:
+        (current_instant - running_thread->get_last_acquisition()) % time_slice == 0)
     {
       running_thread->set_state(Schedulable::state_ready);
-      // We don't set the last_release parameter here. If necessary,
-      // we'll do that below, when selecting a new running thread,
-      // only if it's different from the previous one.
+      running_thread->set_last_release(current_instant);
     }
 
 
+    prepare_ready_queue(*new_snapshot, all_threads);
+
+    // If the policy is preemptible, and we still have a running thread, 
+    // add it to the queue.
+    if(preemptive_policy && is_running(running_thread))
+      _ready_queue->append(*running_thread);
+
     // ?. Ask the policy to sort the queue. If we must select
     // a new thread and it can't run for some reason (it goes blocked, or 
     // terminates), then we remove it from the built ReadyQueue and
-    // check if the next one can run.
-    prepare_ready_queue(*new_snapshot, all_threads);
+    // check if the next one can run (see while loop further below).
     if(_ready_queue->size() > 0) cpu_policy.sort_queue();
 
     // If we don't have to select a new running thread, because the old one didn't
@@ -566,7 +576,11 @@ Scheduler::step_forward(History& history, CPUPolicy& cpu_policy, ResourcePolicy&
     //   * if the current running thread doesn't block, we can perform the final cleanup,
     //     since the queue is already sorted
     //   * else we've to select another running thread, so we continue down in the method
-    if(running_thread != NULL && running_thread->get_state() == Schedulable::state_running)
+    if( // Non-preemptive policy, not ended time-slice:
+       (!preemptive_policy && is_running(running_thread)) || 
+       // Pre-emptive policy, running thread still the first of the queue. 
+       // Note: if is_running(running_thread) == true, then _ready_queue->size() > 0
+       (preemptive_policy && is_running(running_thread) && &_ready_queue->get_item_at(0) == running_thread) )
       {
         raise_new_requests(*running_thread, *new_snapshot, resource_policy); 
         if(running_thread->get_state() != Schedulable::state_blocked)
@@ -602,18 +616,6 @@ Scheduler::step_forward(History& history, CPUPolicy& cpu_policy, ResourcePolicy&
             continue;
           }
 
-        // If the new running is different from the old one,
-        // remember to release our old pal, and to acquire our
-        // new runner.
-        // It'll sufficit that *one* candidate is different from
-        // the old running to trigger this, and it's rightly so.
-        if(&candidate != running_thread)
-          {
-            if(running_thread != NULL)
-              running_thread->set_last_release(current_instant);
-            candidate.set_last_acquisition(current_instant); 
-          }
-
         // Now we check if our candidate blocks on a new request
         raise_new_requests(candidate, *new_snapshot, resource_policy);
         if(candidate.get_state() != Schedulable::state_blocked)
@@ -633,6 +635,19 @@ Scheduler::step_forward(History& history, CPUPolicy& cpu_policy, ResourcePolicy&
       // Fix fields of running thread
       DynamicThread& new_running = (DynamicThread&) _ready_queue->get_item_at(0);
       new_running.set_state(Schedulable::state_running);
+
+      // If the new running is different from the old one,
+      // remember to release our old pal, and to acquire our
+      // new runner.
+      if(&new_running != running_thread)
+        {
+          if(running_thread != NULL)
+            {
+              running_thread->set_state(Schedulable::state_ready);
+              running_thread->set_last_release(current_instant);
+            }
+          new_running.set_last_acquisition(current_instant);
+        }
     }
 
   }
diff --git a/src/text_simulation.cc b/src/text_simulation.cc
index 1572e3b..808c2c9 100644
--- a/src/text_simulation.cc
+++ b/src/text_simulation.cc
@@ -777,6 +777,8 @@ TextSimulation::on_set(const Tokens& arguments)
           if (policy == 0)
           {
             Simulation::get_instance().set_policy(*it);
+            cout << endl << (*it)->get_name() << " scheduling policy selected." << endl;
+
             // FIXME: dedicate a function to set resource policy
             // which includes the following default one
             ResourcePolicyManager & rpm = *ResourcePoliciesGatekeeper::get_instance().get_registered().at(0);
@@ -1001,7 +1003,7 @@ TextSimulation::on_show_cpu_policies(const Tokens& arguments)
     for (CPUPolicyIt it = policies.begin(); it != policies.end(); ++it)
     {
       ostringstream oss;
-      oss << index << ". " << (*it)->get_name() << endl;
+      oss << endl << index << ". " << (*it)->get_name() << endl;
       oss << "\t" << (*it)->get_description() << endl;
 
       p_stdout(oss.str());