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, 1 insertions, 1 deletions

diff --git a/gtk2_ardour/port_matrix.cc b/gtk2_ardour/port_matrix.cc
index 0df5d2214d..60f86ae888 100644
--- a/gtk2_ardour/port_matrix.cc
+++ b/gtk2_ardour/port_matrix.cc
@@ -733,7 +733,7 @@ PortMatrix::remove_channel (ARDOUR::BundleChannel b)
 			int const r = io->remove_port (p, this);
 			if (r == -1) {
 				ArdourDialog d (_("Port removal not allowed"));
-				Label l (_("This port cannot be removed, as the first plugin in the track or buss cannot accept the new number of inputs."));
+				Label l (_("This port cannot be removed.\nEither the first plugin in the track or buss cannot accept\nthe new number of inputs or the last plugin has more outputs."));
 				d.get_vbox()->pack_start (l);
 				d.add_button (Stock::OK, RESPONSE_ACCEPT);
 				d.set_modal (true);