O(1) socket removal

src/socket_base.cpp

@@ -42,7 +42,8 @@ zmq::socket_base_t::socket_base_t (app_thread_t *parent_) :
     pending_term_acks (0),
     ticks (0),
     app_thread (parent_),
-    shutting_down (false)
+    shutting_down (false),
+    index (-1)
 {
 }
 
@@ -379,6 +380,17 @@ void zmq::socket_base_t::detach_outpipe (class writer_t *pipe_)
     out_pipes.pop_back ();
 }
 
+void zmq::socket_base_t::set_index (int index_)
+{
+    index = index_;
+}
+
+int zmq::socket_base_t::get_index ()
+{
+    zmq_assert (index != -1);
+    return index;
+}
+
 void zmq::socket_base_t::process_own (owned_t *object_)
 {
     io_objects.insert (object_);