Prevent deadlock when disconnecting
The backend holds `_port_callback_mutex` while disconnecting ports. In some cases disconnecting a port can drop the last reference resulting in a port-deletion from the connection handler. This in turn will eventually aquire the `_port_callback_mutex` and deadlock. This is now circumvented by using atomic operations instead of taking a lock to set the `_port_change_flag`. The flag is also used to trigger a latency update in some cases, atomic is preferable to taking a lock to set this flag. -- Full bt: https://paste.debian.net/1184056/ Short: #1 in pthread_mutex_lock () #2 in ARDOUR::PortEngineSharedImpl::port_connect_add_remove_callback() #3 in ARDOUR::BackendPort::~BackendPort() #4 in ARDOUR::DummyPort::~DummyPort() #6 in ARDOUR::DummyAudioPort::~DummyAudioPort() #7 in boost::checked_delete<ARDOUR::BackendPort>(ARDOUR::BackendPort*) #12 in boost::shared_ptr<ARDOUR::ProtoPort>::reset() #13 in ARDOUR::Port::drop() #14 in ARDOUR::Port::~Port() #15 in ARDOUR::AudioPort::~AudioPort() #17 in ARDOUR::AudioEngine::add_pending_port_deletion(ARDOUR::Port*) #20 in boost::detail::sp_counted_base::release() #37 in ARDOUR::PortManager::connect_callback() at libs/ardour/port_manager.cc:788 #38 in ARDOUR::DummyAudioBackend::main_process_thread() at libs/backends/dummy/dummy_audiobackend.cc:1018
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@ -183,7 +183,8 @@ protected:
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std::vector<PortConnectData *> _port_connection_queue;
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pthread_mutex_t _port_callback_mutex;
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bool _port_change_flag;
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gint _port_change_flag; /* atomic */
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void port_connect_callback (const std::string& a, const std::string& b, bool conn) {
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pthread_mutex_lock (&_port_callback_mutex);
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@ -192,9 +193,7 @@ protected:
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}
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void port_connect_add_remove_callback () {
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pthread_mutex_lock (&_port_callback_mutex);
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_port_change_flag = true;
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pthread_mutex_unlock (&_port_callback_mutex);
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g_atomic_int_set (&_port_change_flag, 1);
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}
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virtual void update_system_port_latencies ();
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@ -190,7 +190,7 @@ BackendPort::update_connected_latency (bool for_playback)
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PortEngineSharedImpl::PortEngineSharedImpl (PortManager& mgr, std::string const & str)
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: _instance_name (str)
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, _port_change_flag (false)
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, _port_change_flag (0)
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, _portmap (new PortMap)
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, _ports (new PortIndex)
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{
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@ -435,8 +435,8 @@ PortEngineSharedImpl::clear_ports ()
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_ports.flush ();
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_portmap.flush ();
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g_atomic_int_set (&_port_change_flag, 0);
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pthread_mutex_lock (&_port_callback_mutex);
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_port_change_flag = false;
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_port_connection_queue.clear();
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pthread_mutex_unlock (&_port_callback_mutex);
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}
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@ -984,7 +984,7 @@ AlsaAudioBackend::_start (bool for_latency_measurement)
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engine.reconnect_ports ();
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_run = true;
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_port_change_flag = false;
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g_atomic_int_set (&_port_change_flag, 0);
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if (pbd_realtime_pthread_create (PBD_SCHED_FIFO, PBD_RT_PRI_MAIN, PBD_RT_STACKSIZE_PROC,
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&_main_thread, pthread_process, this))
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@ -2039,9 +2039,8 @@ AlsaAudioBackend::main_process_thread ()
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bool connections_changed = false;
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bool ports_changed = false;
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if (!pthread_mutex_trylock (&_port_callback_mutex)) {
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if (_port_change_flag) {
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if (g_atomic_int_compare_and_exchange (&_port_change_flag, 1, 0)) {
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ports_changed = true;
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_port_change_flag = false;
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}
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if (!_port_connection_queue.empty ()) {
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connections_changed = true;
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@ -640,7 +640,7 @@ CoreAudioBackend::_start (bool for_latency_measurement)
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_preinit = true;
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_run = true;
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_port_change_flag = false;
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g_atomic_int_set (&_port_change_flag, 0);
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if (_midi_driver_option == _("CoreMidi")) {
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_midiio->set_enabled(true);
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@ -698,7 +698,7 @@ CoreAudioBackend::_start (bool for_latency_measurement)
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engine.reconnect_ports ();
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// force an initial registration_callback() & latency re-compute
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_port_change_flag = true;
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g_atomic_int_set (&_port_change_flag, 1);
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pre_process ();
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_dsp_load_calc.reset ();
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@ -988,7 +988,7 @@ CoreAudioBackend::coremidi_rediscover()
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#ifndef NDEBUG
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printf("unregister MIDI Output: %s\n", (*it)->name().c_str());
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#endif
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_port_change_flag = true;
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g_atomic_int_set (&_port_change_flag, 1);
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unregister_port((*it));
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it = _system_midi_out.erase(it);
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}
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@ -1008,7 +1008,7 @@ CoreAudioBackend::coremidi_rediscover()
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#ifndef NDEBUG
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printf("unregister MIDI Input: %s\n", (*it)->name().c_str());
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#endif
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_port_change_flag = true;
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g_atomic_int_set (&_port_change_flag, 1);
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unregister_port((*it));
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it = _system_midi_in.erase(it);
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}
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@ -1034,7 +1034,7 @@ CoreAudioBackend::coremidi_rediscover()
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BackendPortPtr pp = boost::dynamic_pointer_cast<BackendPort>(p);
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pp->set_hw_port_name(_midiio->port_name(i, true));
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_system_midi_in.push_back(pp);
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_port_change_flag = true;
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g_atomic_int_set (&_port_change_flag, 1);
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}
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for (size_t i = 0; i < _midiio->n_midi_outputs(); ++i) {
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@ -1057,7 +1057,7 @@ CoreAudioBackend::coremidi_rediscover()
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BackendPortPtr pp = boost::dynamic_pointer_cast<BackendPort>(p);
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pp->set_hw_port_name(_midiio->port_name(i, false));
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_system_midi_out.push_back(pp);
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_port_change_flag = true;
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g_atomic_int_set (&_port_change_flag, 1);
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}
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@ -1229,9 +1229,8 @@ CoreAudioBackend::pre_process ()
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bool connections_changed = false;
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bool ports_changed = false;
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if (!pthread_mutex_trylock (&_port_callback_mutex)) {
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if (_port_change_flag) {
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if (g_atomic_int_compare_and_exchange (&_port_change_flag, 1, 0)) {
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ports_changed = true;
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_port_change_flag = false;
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}
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if (!_port_connection_queue.empty ()) {
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connections_changed = true;
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@ -460,7 +460,7 @@ DummyAudioBackend::_start (bool /*for_latency_measurement*/)
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}
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engine.reconnect_ports ();
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_port_change_flag = false;
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g_atomic_int_set (&_port_change_flag, 0);
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if (pbd_pthread_create (PBD_RT_STACKSIZE_PROC, &_main_thread, pthread_process, this)) {
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PBD::error << _("DummyAudioBackend: cannot start.") << endmsg;
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@ -1006,9 +1006,8 @@ DummyAudioBackend::main_process_thread ()
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bool connections_changed = false;
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bool ports_changed = false;
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if (!pthread_mutex_trylock (&_port_callback_mutex)) {
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if (_port_change_flag) {
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if (g_atomic_int_compare_and_exchange (&_port_change_flag, 1, 0)) {
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ports_changed = true;
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_port_change_flag = false;
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}
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if (!_port_connection_queue.empty ()) {
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connections_changed = true;
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@ -636,8 +636,6 @@ PortAudioBackend::_start (bool for_latency_measurement)
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_measure_latency = for_latency_measurement;
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_port_change_flag = false;
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if (_midi_driver_option == winmme_driver_name) {
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_midiio->set_enabled(true);
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//_midiio->set_port_changed_callback(midi_port_change, this);
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@ -674,7 +672,7 @@ PortAudioBackend::_start (bool for_latency_measurement)
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_run = true;
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engine.reconnect_ports ();
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_port_change_flag = false;
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g_atomic_int_set (&_port_change_flag, 0);
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_dsp_calc.reset ();
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@ -1728,9 +1726,8 @@ PortAudioBackend::process_port_connection_changes ()
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bool connections_changed = false;
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bool ports_changed = false;
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if (!pthread_mutex_trylock (&_port_callback_mutex)) {
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if (_port_change_flag) {
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if (g_atomic_int_compare_and_exchange (&_port_change_flag, 1, 0)) {
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ports_changed = true;
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_port_change_flag = false;
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}
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if (!_port_connection_queue.empty ()) {
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connections_changed = true;
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@ -625,7 +625,7 @@ PulseAudioBackend::_start (bool /*for_latency_measurement*/)
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engine.reconnect_ports ();
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_run = true;
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_port_change_flag = false;
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g_atomic_int_set (&_port_change_flag, 0);
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if (pbd_realtime_pthread_create (PBD_SCHED_FIFO, PBD_RT_PRI_MAIN, PBD_RT_STACKSIZE_PROC,
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&_main_thread, pthread_process, this)) {
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@ -1104,9 +1104,8 @@ PulseAudioBackend::main_process_thread ()
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bool connections_changed = false;
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bool ports_changed = false;
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if (!pthread_mutex_trylock (&_port_callback_mutex)) {
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if (_port_change_flag) {
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ports_changed = true;
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_port_change_flag = false;
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if (g_atomic_int_compare_and_exchange (&_port_change_flag, 1, 0)) {
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ports_changed = true;
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}
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if (!_port_connection_queue.empty ()) {
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connections_changed = true;
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