clean up functors used in cross-thread call_slot() messages, in case they contain...

diff --git a/libs/pbd/pbd/abstract_ui.cc b/libs/pbd/pbd/abstract_ui.cc
index 65f321222ec83d4eaba6bb49981d4fa439384f0b..40b4ea8d9361419a08fab8e226ca374ebff80681 100644 (file)
--- a/libs/pbd/pbd/abstract_ui.cc
+++ b/libs/pbd/pbd/abstract_ui.cc
@@ -224,6 +224,19 @@ AbstractUI<RequestObject>::handle_ui_requests ()
                                        request_buffer_map_lock.unlock ();
                                        DEBUG_TRACE (PBD::DEBUG::AbstractUI, string_compose ("%1: valid request, calling ::do_request()\n", event_loop_name()));
                                        do_request (vec.buf[0]);
+
+                                       /* if the request was CallSlot, then we need to ensure that we reset the functor in the request, in case it
+                                        * held a shared_ptr<>. Failure to do so can lead to dangling references to objects passed to PBD::Signals.
+                                        *
+                                        * Note that this method (::handle_ui_requests()) is by definition called from the event loop thread, so
+                                        * caller_is_self() is true, which means that the execution of the functor has definitely happened after
+                                        * do_request() returns and we no longer need the functor for any reason.
+                                        */
+
+                                       if (vec.buf[0]->type == CallSlot) {
+                                               vec.buf[0]->the_slot = 0;
+                                       }
+
                                        request_buffer_map_lock.lock ();
                                        if (vec.buf[0]->invalidation) {
                                                DEBUG_TRACE (PBD::DEBUG::AbstractUI, string_compose ("%1: removing invalidation record for that request\n", event_loop_name()));