Prevent delay-line reconfiguration while processing

Various backends have different strategies for updating latencies,
and different thread semantics for latency update callbacks.

With jack2 it is possible that processing happens concurrently
while port latencies are being changed.

Ardour internal backends emit the latency callback from the
main process thread, serializing latency changes with processing.

Various user actions can also trigger latency changes. e.g.
with a stopped engine it is possible to re-order plugins.

1 files changed, 8 insertions, 5 deletions

diff --git a/libs/ardour/route.cc b/libs/ardour/route.cc
index c50b4aab25..e9e2e4604b 100644
--- a/libs/ardour/route.cc
+++ b/libs/ardour/route.cc
@@ -2202,6 +2202,8 @@ Route::reorder_processors (const ProcessorList& new_order, ProcessorStreams* err
 			_pending_processor_order.clear ();
 			setup_invisible_processors ();
 
+			update_signal_latency (true);
+
 			processors_changed (RouteProcessorChange ()); /* EMIT SIGNAL */
 			set_processor_positions ();
 		} else {
@@ -2226,6 +2228,12 @@ Route::reorder_processors (const ProcessorList& new_order, ProcessorStreams* err
 		}
 
 		lm.release();
+
+		/* update processor input/output latency (total signal_latency does not change).
+		 * delaylines may changes, so the Engine Lock is required.
+		 */
+		update_signal_latency (true);
+
 		lx.release();
 
 		processors_changed (RouteProcessorChange ()); /* EMIT SIGNAL */
@@ -2240,11 +2248,6 @@ Route::reorder_processors (const ProcessorList& new_order, ProcessorStreams* err
 		g_atomic_int_set (&_pending_process_reorder, 1);
 	}
 
-	/* update processor input/output latency
-	 * (total signal_latency does not change)
-	 */
-	update_signal_latency (true);
-
 	return 0;
 }