Add callback support for zero counter event in shared_base

3 files changed, 31 insertions, 3 deletions

diff --git a/odb/shared-ptr/base.cxx b/odb/shared-ptr/base.cxx
index 56fc32c..197d20b 100644
--- a/odb/shared-ptr/base.cxx
+++ b/odb/shared-ptr/base.cxx
@@ -21,6 +21,20 @@ namespace odb
   {
     return "object is not shared";
   }
+
+  bool shared_base::
+  _dec_ref_callback ()
+  {
+    bool r (--counter_ == 0);
+
+    if (r)
+    {
+      callback_->zero_counter (callback_->arg);
+      r = (counter_ == 0);
+    }
+
+    return r;
+  }
 }
 
 //
diff --git a/odb/shared-ptr/base.hxx b/odb/shared-ptr/base.hxx
index 6fdc32e..4766aa7 100644
--- a/odb/shared-ptr/base.hxx
+++ b/odb/shared-ptr/base.hxx
@@ -68,8 +68,19 @@ namespace odb
     void
     operator delete (void*) throw ();
 
+    struct refcount_callback
+    {
+      void* arg;
+      void (*zero_counter) (void*);
+    };
+
+  private:
+    bool
+    _dec_ref_callback ();
+
   protected:
     std::size_t counter_;
+    refcount_callback* callback_;
   };
 
   template <typename X>
diff --git a/odb/shared-ptr/base.ixx b/odb/shared-ptr/base.ixx
index ee27fbe..61270a3 100644
--- a/odb/shared-ptr/base.ixx
+++ b/odb/shared-ptr/base.ixx
@@ -25,13 +25,13 @@ namespace odb
 
   inline shared_base::
   shared_base ()
-      : counter_ (1)
+      : counter_ (1), callback_ (0)
   {
   }
 
   inline shared_base::
   shared_base (const shared_base&)
-      : counter_ (1)
+      : counter_ (1), callback_ (0)
   {
   }
 
@@ -50,7 +50,10 @@ namespace odb
   inline bool shared_base::
   _dec_ref ()
   {
-    return --counter_ == 0;
+    if (callback_ == 0)
+      return --counter_ == 0;
+    else
+      return _dec_ref_callback ();
   }
 
   inline std::size_t shared_base::