fix a deadlock with jack2 when inserting a plugin adds ports.

When adding a processor, the processor may add ports leading to
a call to jack_port_register(). while Ardour holds a WritertLock on the
processor-list (this commit removes this WriterLock).

with jack2 that results in a graph-reorder callback (WHY?)

jack2 issues that graph-reorder in a separate thread BUT
port-registration does not return until the graph-reorder is complete.

On Ardour's side, graph_reordered() calls Session::resort_routes ()
which eventually checks Route::direct_feeds_according_to_reality()
which needs a ReadLock on the processor-list to check I/O.

Since jack_port_register() does not return, this constitutes a deadlock.

THE ACTUAL PROBLEM IS JACK2's THREAD DESIGN!
Why does jack_port_register() trigger a graph-order in jack2?
No connections are made.
..and why does it block jack_port_register() from returning if
that graph-order callback is in a different thread?
http://pastebin.com/DZANXJLz

1 files changed, 1 insertions, 1 deletions

diff --git a/libs/ardour/ardour/route.h b/libs/ardour/ardour/route.h
index 66a83cf67d..bac33ae7a1 100644
--- a/libs/ardour/ardour/route.h
+++ b/libs/ardour/ardour/route.h
@@ -848,7 +848,7 @@ class LIBARDOUR_API Route : public SessionObject, public Automatable, public Rou
 	bool _initial_io_setup;
 	bool _in_sidechain_setup;
 
-	int configure_processors_unlocked (ProcessorStreams*);
+	int configure_processors_unlocked (ProcessorStreams*, Glib::Threads::RWLock::WriterLock*);
 	bool set_meter_point_unlocked ();
 	void apply_processor_order (const ProcessorList& new_order);