ALSA: add locks to safely add/remove MIDI devices

Theoretically this could be lock-free by using a queue of device
ports to be added/remove in sync in the process-callback, but
realistically adding/removing devices doesn't have to be rt-safe.

1 files changed, 24 insertions, 2 deletions

diff --git a/libs/backends/alsa/alsa_audiobackend.cc b/libs/backends/alsa/alsa_audiobackend.cc
index 3266853bca..1355197522 100644
--- a/libs/backends/alsa/alsa_audiobackend.cc
+++ b/libs/backends/alsa/alsa_audiobackend.cc
@@ -78,6 +78,7 @@ AlsaAudioBackend::AlsaAudioBackend (AudioEngine& e, AudioBackendInfo& info)
 {
 	_instance_name = s_instance_name;
 	pthread_mutex_init (&_port_callback_mutex, 0);
+	pthread_mutex_init (&_device_port_mutex, 0);
 	_input_audio_device_info.valid = false;
 	_output_audio_device_info.valid = false;
 
@@ -87,6 +88,7 @@ AlsaAudioBackend::AlsaAudioBackend (AudioEngine& e, AudioBackendInfo& info)
 AlsaAudioBackend::~AlsaAudioBackend ()
 {
 	pthread_mutex_destroy (&_port_callback_mutex);
+	pthread_mutex_destroy (&_device_port_mutex);
 }
 
 /* AUDIOBACKEND API */
@@ -474,6 +476,7 @@ AlsaAudioBackend::update_systemic_audio_latencies ()
 void
 AlsaAudioBackend::update_systemic_midi_latencies ()
 {
+	pthread_mutex_lock (&_device_port_mutex);
 	uint32_t i = 0;
 	for (std::vector<AlsaPort*>::iterator it = _system_midi_out.begin (); it != _system_midi_out.end (); ++it, ++i) {
 		assert (_rmidi_out.size() > i);
@@ -495,6 +498,7 @@ AlsaAudioBackend::update_systemic_midi_latencies ()
 		lr.min = lr.max = (_measure_latency ? 0 : nfo->systemic_input_latency);
 		set_latency_range (*it, true, lr);
 	}
+	pthread_mutex_unlock (&_device_port_mutex);
 	update_latencies ();
 }
 
@@ -682,6 +686,7 @@ AlsaAudioBackend::set_midi_device_enabled (std::string const device, bool enable
 			register_system_midi_ports(device);
 		} else {
 			// remove all ports provided by the given device
+			pthread_mutex_lock (&_device_port_mutex);
 			uint32_t i = 0;
 			for (std::vector<AlsaPort*>::iterator it = _system_midi_out.begin (); it != _system_midi_out.end ();) {
 				assert (_rmidi_out.size() > i);
@@ -705,6 +710,7 @@ AlsaAudioBackend::set_midi_device_enabled (std::string const device, bool enable
 				_rmidi_in.erase (_rmidi_in.begin() + i);
 				delete rm;
 			}
+			pthread_mutex_unlock (&_device_port_mutex);
 		}
 		update_systemic_midi_latencies ();
 	}
@@ -1540,12 +1546,14 @@ AlsaAudioBackend::update_system_port_latecies ()
 		(*it)->update_connected_latency (false);
 	}
 
+	pthread_mutex_lock (&_device_port_mutex);
 	for (std::vector<AlsaPort*>::const_iterator it = _system_midi_in.begin (); it != _system_midi_in.end (); ++it) {
 		(*it)->update_connected_latency (true);
 	}
 	for (std::vector<AlsaPort*>::const_iterator it = _system_midi_out.begin (); it != _system_midi_out.end (); ++it) {
 		(*it)->update_connected_latency (false);
 	}
+	pthread_mutex_unlock (&_device_port_mutex);
 
 	for (AudioSlaves::iterator s = _slaves.begin (); s != _slaves.end (); ++s) {
 		if ((*s)->dead) {
@@ -1648,7 +1656,9 @@ AlsaAudioBackend::register_system_midi_ports(const std::string device)
 				static_cast<AlsaMidiPort*>(p)->set_n_periods(_periods_per_cycle); // TODO check MIDI alignment
 				AlsaPort *ap = static_cast<AlsaPort*>(p);
 				ap->set_pretty_name (replace_name_io (i->first, false));
+				pthread_mutex_lock (&_device_port_mutex);
 				_system_midi_out.push_back (ap);
+				pthread_mutex_unlock (&_device_port_mutex);
 				_rmidi_out.push_back (mout);
 			}
 		}
@@ -1687,7 +1697,9 @@ AlsaAudioBackend::register_system_midi_ports(const std::string device)
 				set_latency_range (p, false, lr);
 				AlsaPort *ap = static_cast<AlsaPort*>(p);
 				ap->set_pretty_name (replace_name_io (i->first, true));
+				pthread_mutex_lock (&_device_port_mutex);
 				_system_midi_in.push_back (ap);
+				pthread_mutex_unlock (&_device_port_mutex);
 				_rmidi_in.push_back (midin);
 			}
 		}
@@ -2170,6 +2182,8 @@ AlsaAudioBackend::main_process_thread ()
 					}
 				}
 
+				/* only used when adding/removing MIDI device/system ports */
+				pthread_mutex_lock (&_device_port_mutex);
 				/* de-queue incoming midi*/
 				i = 0;
 				for (std::vector<AlsaPort*>::const_iterator it = _system_midi_in.begin (); it != _system_midi_in.end (); ++it, ++i) {
@@ -2186,6 +2200,7 @@ AlsaAudioBackend::main_process_thread ()
 					}
 					rm->sync_time (clock1);
 				}
+				pthread_mutex_unlock (&_device_port_mutex);
 
 				for (std::vector<AlsaPort*>::const_iterator it = _system_outputs.begin (); it != _system_outputs.end (); ++it) {
 					memset ((*it)->get_buffer (_samples_per_period), 0, _samples_per_period * sizeof (Sample));
@@ -2199,6 +2214,8 @@ AlsaAudioBackend::main_process_thread ()
 					return 0;
 				}
 
+				/* only used when adding/removing MIDI device/system ports */
+				pthread_mutex_lock (&_device_port_mutex);
 				for (std::vector<AlsaPort*>::iterator it = _system_midi_out.begin (); it != _system_midi_out.end (); ++it) {
 					static_cast<AlsaMidiPort*>(*it)->next_period();
 				}
@@ -2214,6 +2231,7 @@ AlsaAudioBackend::main_process_thread ()
 						rm->send_event (mit->timestamp (), mit->data (), mit->size ());
 					}
 				}
+				pthread_mutex_unlock (&_device_port_mutex);
 
 				/* write back audio */
 				i = 0;
@@ -2265,6 +2283,7 @@ AlsaAudioBackend::main_process_thread ()
 
 			clock1 = g_get_monotonic_time();
 			uint32_t i = 0;
+			pthread_mutex_lock (&_device_port_mutex);
 			for (std::vector<AlsaPort*>::const_iterator it = _system_midi_in.begin (); it != _system_midi_in.end (); ++it, ++i) {
 				static_cast<AlsaMidiBuffer*>((*it)->get_buffer(0))->clear ();
 				AlsaMidiIn *rm = _rmidi_in.at(i);
@@ -2280,6 +2299,7 @@ AlsaAudioBackend::main_process_thread ()
 				}
 				rm->sync_time (clock1);
 			}
+			pthread_mutex_unlock (&_device_port_mutex);
 
 			_last_process_start = 0;
 			if (engine.process_callback (_samples_per_period)) {
@@ -2289,10 +2309,12 @@ AlsaAudioBackend::main_process_thread ()
 			}
 
 			// drop all outgoing MIDI messages
+			pthread_mutex_lock (&_device_port_mutex);
 			for (std::vector<AlsaPort*>::const_iterator it = _system_midi_out.begin (); it != _system_midi_out.end (); ++it) {
-					void *bptr = (*it)->get_buffer(0);
-					midi_clear(bptr);
+				void *bptr = (*it)->get_buffer(0);
+				midi_clear(bptr);
 			}
+			pthread_mutex_unlock (&_device_port_mutex);
 
 			_dsp_load = 1.0;
 			reset_dll = true;