traffic-control: (fixes #2940) QueueDisc SojournTime should be TracedCallback

TracedCallback is invoked for all sojourn time results; TracedValue only
for results that changed value from last time

CHANGES.html

@@ -93,6 +93,7 @@ or with a string value with 'b' (bytes) or 'p' (packets) suffix, such as:
   <li>QueueDisc::DequeuePeeked has been merged into QueueDisc::Dequeue and hence no longer exists.</li>
   <li>The QueueDisc base class now provides a default implementation of the DoPeek private method
   based on the QueueDisc::PeekDequeue method, which is now no longer available.</li>
+  <li>The QueueDisc::SojournTime trace source is changed from a TracedValue to a TracedCallback; callbacks that hook this trace must provide one ns3::Time argument, not two.</li>
 </ul>
 <h2>Changes to build system:</h2>
 <ul>

examples/traffic-control/traffic-control.cc

@@ -79,9 +79,9 @@ DevicePacketsInQueueTrace (uint32_t oldValue, uint32_t newValue)
 }
 
 void
-SojournTimeTrace (Time oldValue, Time newValue)
+SojournTimeTrace (Time sojournTime)
 {
-  std::cout << "Sojourn time " << newValue.ToDouble (Time::MS) << "ms" << std::endl;
+  std::cout << "Sojourn time " << sojournTime.ToDouble (Time::MS) << "ms" << std::endl;
 }
 
 int

src/traffic-control/model/queue-disc.cc

@@ -317,7 +317,7 @@ TypeId QueueDisc::GetTypeId (void)
     .AddTraceSource ("SojournTime",
                      "Sojourn time of the last packet dequeued from the queue disc",
                      MakeTraceSourceAccessor (&QueueDisc::m_sojourn),
-                     "ns3::TracedValueCallback::Time")
+                     "ns3::Time::TracedCallback")
   ;
   return tid;
 }
@@ -325,7 +325,6 @@ TypeId QueueDisc::GetTypeId (void)
 QueueDisc::QueueDisc (QueueDiscSizePolicy policy)
   :  m_nPackets (0),
      m_nBytes (0),
-     m_sojourn (0),
      m_maxSize (QueueSize ("1p")),         // to avoid that setting the mode at construction time is ignored
      m_running (false),
      m_peeked (false),
@@ -702,7 +701,7 @@ QueueDisc::PacketDequeued (Ptr<const QueueDiscItem> item)
       m_stats.nTotalDequeuedPackets++;
       m_stats.nTotalDequeuedBytes += item->GetSize ();
 
-      m_sojourn = Simulator::Now () - item->GetTimeStamp ();
+      m_sojourn (Simulator::Now () - item->GetTimeStamp ());
 
       NS_LOG_LOGIC ("m_traceDequeue (p)");
       m_traceDequeue (item);

src/traffic-control/model/queue-disc.h

@@ -22,6 +22,7 @@
 
 #include "ns3/object.h"
 #include "ns3/traced-value.h"
+#include "ns3/traced-callback.h"
 #include "ns3/net-device.h"
 #include "ns3/queue-item.h"
 #include "ns3/queue-size.h"
@@ -665,7 +666,7 @@ private:
 
   TracedValue<uint32_t> m_nPackets; //!< Number of packets in the queue
   TracedValue<uint32_t> m_nBytes;   //!< Number of bytes in the queue
-  TracedValue<Time> m_sojourn;      //!< Sojourn time of the latest dequeued packet
+  TracedCallback<Time> m_sojourn;   //!< Sojourn time of the latest dequeued packet
   QueueSize m_maxSize;              //!< max queue size
 
   Stats m_stats;                    //!< The collected statistics