core: Make reference counting thread-safe

src/core/CMakeLists.txt

@@ -229,6 +229,7 @@ set(header_files
     model/ascii-file.h
     model/ascii-test.h
     model/assert.h
+    model/atomic-counter.h
     model/attribute-accessor-helper.h
     model/attribute-construction-list.h
     model/attribute-container-accessor-helper.h

src/core/model/atomic-counter.h

@@ -0,0 +1,49 @@
+/* -*- Mode:C++; c-file-style:"gnu"; indent-tabs-mode:nil; -*- */
+#ifndef ATOMIC_COUNTER_H
+#define ATOMIC_COUNTER_H
+
+#include <atomic>
+
+namespace ns3 {
+
+class AtomicCounter
+{
+public:
+  inline AtomicCounter ()
+  {
+    m_count.store (0, std::memory_order_release);
+  }
+
+  inline AtomicCounter (uint32_t count)
+  {
+    m_count.store (count, std::memory_order_release);
+  }
+
+  inline operator uint32_t () const
+  {
+    return m_count.load (std::memory_order_acquire);
+  }
+
+  inline uint32_t operator = (const uint32_t count)
+  {
+    m_count.store (count, std::memory_order_release);
+    return count;
+  }
+
+  inline uint32_t operator++ (int)
+  {
+    return m_count.fetch_add (1, std::memory_order_relaxed);
+  }
+
+  inline uint32_t operator-- (int)
+  {
+    return m_count.fetch_sub (1, std::memory_order_release);
+  }
+
+private:
+  std::atomic<uint32_t> m_count;
+};
+
+} // namespace ns3
+
+#endif /* ATOMIC_COUNTER_H */

src/core/model/simple-ref-count.h

@@ -22,6 +22,7 @@
 #ifndef SIMPLE_REF_COUNT_H
 #define SIMPLE_REF_COUNT_H
 
+#include "atomic-counter.h"
 #include "empty.h"
 #include "default-deleter.h"
 #include "assert.h"
@@ -112,9 +113,11 @@ public:
    */
   inline void Unref (void) const
   {
-    m_count--;
-    if (m_count == 0)
+    if (m_count-- == 1)
       {
+#ifdef NS3_MTP
+        std::atomic_thread_fence (std::memory_order_acquire);
+#endif
         DELETER::Delete (static_cast<T*> (const_cast<SimpleRefCount *> (this)));
       }
   }
@@ -138,7 +141,11 @@ private:
    * Note we make this mutable so that the const methods can still
    * change it.
    */
+#ifdef NS3_MTP
+  mutable AtomicCounter m_count;
+#else
   mutable uint32_t m_count;
+#endif
 };
 
 } // namespace ns3