Work around Jack returning NULL buffers

2 files changed, 15 insertions, 3 deletions

diff --git a/src/server/JackDriver.cpp b/src/server/JackDriver.cpp
index d022077a..973e3eb7 100644
--- a/src/server/JackDriver.cpp
+++ b/src/server/JackDriver.cpp
@@ -125,6 +125,10 @@ JackDriver::attach(const std::string& server_name,
 	_block_length = jack_get_buffer_size(_client);
 	_seq_size     = jack_port_type_get_buffer_size(_client, JACK_DEFAULT_MIDI_TYPE);
 
+	_fallback_buffer = AudioBufPtr(
+		static_cast<float*>(
+			Buffer::aligned_alloc(sizeof(float) * _block_length)));
+
 	jack_on_shutdown(_client, shutdown_cb, this);
 
 	jack_set_thread_init_callback(_client, thread_init_cb, this);
@@ -217,7 +221,12 @@ JackDriver::add_port(RunContext& context, EnginePort* port)
 		const SampleCount nframes = context.nframes();
 		jack_port_t*      jport   = (jack_port_t*)port->handle();
 		void*             jbuf    = jack_port_get_buffer(jport, nframes);
-		graph_port->set_driver_buffer(jbuf, nframes * sizeof(float));
+
+		/* Jack fails to return a buffer if this is too soon after registering
+		   the port, so use a silent fallback buffer if necessary. */
+		graph_port->set_driver_buffer(
+			jbuf ? jbuf : _fallback_buffer.get(),
+			nframes * sizeof(float));
 	}
 }
 
diff --git a/src/server/JackDriver.hpp b/src/server/JackDriver.hpp
index 678ce483..2a21d96e 100644
--- a/src/server/JackDriver.hpp
+++ b/src/server/JackDriver.hpp
@@ -29,9 +29,9 @@
 #include <jack/session.h>
 #endif
 
-#include "raul/Semaphore.hpp"
-
+#include "ingen/types.hpp"
 #include "lv2/lv2plug.in/ns/ext/atom/forge.h"
+#include "raul/Semaphore.hpp"
 
 #include "Driver.hpp"
 #include "EnginePort.hpp"
@@ -142,8 +142,11 @@ protected:
 	                                boost::intrusive::cache_last<true>
 	                                > Ports;
 
+	using AudioBufPtr = UPtr<float, FreeDeleter<float>>;
+
 	Engine&                _engine;
 	Ports                  _ports;
+	AudioBufPtr            _fallback_buffer;
 	LV2_Atom_Forge         _forge;
 	Raul::Semaphore        _sem;
 	std::atomic<bool>      _flag;