+namespace s4u {
+class Actor;
+class Comm;
+class Host;
+class Link;
+class Mailbox;
+class NetZone;
+
+XBT_PUBLIC(void) intrusive_ptr_release(Comm* c);
+XBT_PUBLIC(void) intrusive_ptr_add_ref(Comm* c);
+}
+namespace kernel {
+namespace activity {
+class ActivityImpl;