core: make insertion order of CalendarScheduler configurable

src/core/model/calendar-scheduler.cc

@@ -109,7 +109,7 @@ CalendarScheduler::DoInsert (const Event &ev)
   Bucket::iterator end = m_buckets[bucket].end ();
   for (Bucket::iterator i = m_buckets[bucket].begin (); i != end; ++i)
     {
-      if (ev.key > i->key)
+      if ((ev.key < i->key && !m_reverse) || (ev.key > i->key && m_reverse))
         {
           m_buckets[bucket].insert (i, ev);
           return;
@@ -148,7 +148,7 @@ CalendarScheduler::PeekNext (void) const
     {
       if (!m_buckets[i].empty ())
         {
-          Scheduler::Event next = m_buckets[i].back ();
+          Scheduler::Event next = m_reverse ? m_buckets[i].back () : m_buckets[i].front ();
           if (next.key.m_ts < bucketTop)
             {
               return next;
@@ -184,13 +184,13 @@ CalendarScheduler::DoRemoveNext (void)
     {
       if (!m_buckets[i].empty ())
         {
-          Scheduler::Event next = m_buckets[i].back ();
+          Scheduler::Event next = m_reverse ? m_buckets[i].back () : m_buckets[i].front ();
           if (next.key.m_ts < bucketTop)
             {
               m_lastBucket = i;
               m_lastPrio = next.key.m_ts;
               m_bucketTop = bucketTop;
-              m_buckets[i].pop_back ();
+              m_reverse ? m_buckets[i].pop_back () : m_buckets[i].pop_front ();
               return next;
             }
           if (next.key < minKey)
@@ -208,8 +208,8 @@ CalendarScheduler::DoRemoveNext (void)
   m_lastPrio = minKey.m_ts;
   m_lastBucket = Hash (minKey.m_ts);
   m_bucketTop = (minKey.m_ts / m_width + 1) * m_width;
-  Scheduler::Event next = m_buckets[minBucket].back ();
-  m_buckets[minBucket].pop_back ();
+  Scheduler::Event next = m_reverse ? m_buckets[minBucket].back () : m_buckets[minBucket].front();
+  m_reverse ? m_buckets[minBucket].pop_back () : m_buckets[minBucket].pop_front ();
 
   return next;
 }
@@ -383,4 +383,13 @@ CalendarScheduler::Resize (uint32_t newSize)
   DoResize (newSize, newWidth);
 }
 
+bool CalendarScheduler::SetReverse (bool reverse)
+{
+	NS_LOG_FUNCTION (this << reverse);
+
+	bool old_reverse = m_reverse;
+	m_reverse = reverse;
+	return old_reverse;
+}
+
 } // namespace ns3

src/core/model/calendar-scheduler.h

@@ -48,6 +48,12 @@ class EventImpl;
  * the original algorithm (to the best of my knowledge).
  *
  * \note
+ * This queue is much slower than I expected (much slower than the
+ * std::map queue) and this seems to be because the original resizing policy
+ * is horribly bad.  This is most likely the reason why there have been
+ * so many variations published which all slightly tweak the resizing
+ * heuristics to obtain a better distribution of events across buckets.
+ *
  * While inserion sort is not discussed in the original article, its
  * implementation appears to dramatically affect performance.
  * CalendarScheduler sorts buckets in \em reverse chronological order.
@@ -77,6 +83,8 @@ public:
   virtual Scheduler::Event RemoveNext (void);
   virtual void Remove (const Scheduler::Event &ev);
 
+  bool SetReverse (bool reverse);
+
 private:
   /** Double the number of buckets if necessary. */
   void ResizeUp (void);
@@ -150,6 +158,8 @@ private:
   uint64_t m_lastPrio;
   /** Number of events in queue. */
   uint32_t m_qSize;
+  /** Switch between old and new configuration after bug 2498. */
+  bool m_reverse = false;
 };
 
 } // namespace ns3