disallow invalid port-removal

do not allow port-removal if the port would be re-added immediately
after that again because the main-delivery actually needs it.

As a side effect this prevents this crash:

 * create a stereo-track, then remove one output
  -> unhandled exception "AudioEngine::PortRegistrationFailure&"

 The problem:
 - the port is removed from the RCU ports list,
   but Port::drop() (which calls jack_port_unregister) is only called
   from the Port's destructor at some later time.
   (because a reference to the port still exists elsewhere)
 - the jack-port is not yet removed.
 - meanwhile Delivery::configure_io comes along and notices that
   there are more audio-buffers than ports and tries to re-register the port.
 - but the port still exists in jack, so it fails and throws an exception
   ...which is not handled.

1 files changed, 2 insertions, 0 deletions

diff --git a/libs/ardour/ardour/route.h b/libs/ardour/ardour/route.h
index 2e44d00984..f0987fa77e 100644
--- a/libs/ardour/ardour/route.h
+++ b/libs/ardour/ardour/route.h
@@ -530,6 +530,7 @@ class Route : public SessionObject, public Automatable, public RouteGroupMember,
 	void silence_unlocked (framecnt_t);
 
 	ChanCount processor_max_streams;
+	ChanCount processor_out_streams;
 
 	uint32_t pans_required() const;
 	ChanCount n_process_buffers ();
@@ -553,6 +554,7 @@ class Route : public SessionObject, public Automatable, public RouteGroupMember,
 	void output_change_handler (IOChange, void *src);
 
 	bool input_port_count_changing (ChanCount);
+	bool output_port_count_changing (ChanCount);
 
 	bool _in_configure_processors;