Fix a deadlock issue when shutting down ALSA cards.

diff --git a/alsa_input.cpp b/alsa_input.cpp
index 22daf760b026cb8c27cd8b4604ab41488667f345..bfadacb142734cd746fd6a1788d7838fbeb0e8f4 100644 (file)
--- a/alsa_input.cpp
+++ b/alsa_input.cpp
@@ -125,7 +125,11 @@ void ALSAInput::capture_thread_func()
 
                const int64_t prev_pts = frames_to_pts(num_frames_output);
                const int64_t pts = frames_to_pts(num_frames_output + frames);
-               audio_callback(buffer.get(), frames, audio_format, pts - prev_pts);
+               bool success;
+               do {
+                       if (should_quit) return;
+                       success = audio_callback(buffer.get(), frames, audio_format, pts - prev_pts);
+               } while (!success);
                num_frames_output += frames;
        }
 }

diff --git a/alsa_input.h b/alsa_input.h
index d485a3b74e18b1ce823c5dbf9d5ea7df08ad1ce2..895760fed8fef76737e341e44e188267db7c9692 100644 (file)
--- a/alsa_input.h
+++ b/alsa_input.h
@@ -22,7 +22,7 @@
 
 class ALSAInput {
 public:
-       typedef std::function<void(const uint8_t *data, unsigned num_samples, bmusb::AudioFormat audio_format, int64_t frame_length)> audio_callback_t;
+       typedef std::function<bool(const uint8_t *data, unsigned num_samples, bmusb::AudioFormat audio_format, int64_t frame_length)> audio_callback_t;
 
        ALSAInput(const char *device, unsigned sample_rate, unsigned num_channels, audio_callback_t audio_callback);
        ~ALSAInput();

diff --git a/audio_mixer.cpp b/audio_mixer.cpp
index acd48c5e0903775bcb598d452f3bcb28e04225ef..1c570fa870468e54134ac892c5eac016372754ce 100644 (file)
--- a/audio_mixer.cpp
+++ b/audio_mixer.cpp
@@ -123,7 +123,7 @@ AudioMixer::~AudioMixer()
 
 void AudioMixer::reset_resampler(DeviceSpec device_spec)
 {
-       lock_guard<mutex> lock(audio_mutex);
+       lock_guard<timed_mutex> lock(audio_mutex);
        reset_resampler_mutex_held(device_spec);
 }
 
@@ -159,14 +159,17 @@ void AudioMixer::reset_alsa_mutex_held(DeviceSpec device_spec)
        }
 }
 
-void AudioMixer::add_audio(DeviceSpec device_spec, const uint8_t *data, unsigned num_samples, AudioFormat audio_format, int64_t frame_length)
+bool AudioMixer::add_audio(DeviceSpec device_spec, const uint8_t *data, unsigned num_samples, AudioFormat audio_format, int64_t frame_length)
 {
        AudioDevice *device = find_audio_device(device_spec);
 
-       lock_guard<mutex> lock(audio_mutex);
+       unique_lock<timed_mutex> lock(audio_mutex, defer_lock);
+       if (!lock.try_lock_for(chrono::milliseconds(10))) {
+               return false;
+       }
        if (device->resampling_queue == nullptr) {
                // No buses use this device; throw it away.
-               return;
+               return true;
        }
 
        unsigned num_channels = device->interesting_channels.size();
@@ -200,16 +203,20 @@ void AudioMixer::add_audio(DeviceSpec device_spec, const uint8_t *data, unsigned
        int64_t local_pts = device->next_local_pts;
        device->resampling_queue->add_input_samples(local_pts / double(TIMEBASE), audio.data(), num_samples);
        device->next_local_pts = local_pts + frame_length;
+       return true;
 }
 
-void AudioMixer::add_silence(DeviceSpec device_spec, unsigned samples_per_frame, unsigned num_frames, int64_t frame_length)
+bool AudioMixer::add_silence(DeviceSpec device_spec, unsigned samples_per_frame, unsigned num_frames, int64_t frame_length)
 {
        AudioDevice *device = find_audio_device(device_spec);
 
-       lock_guard<mutex> lock(audio_mutex);
+       unique_lock<timed_mutex> lock(audio_mutex, defer_lock);
+       if (!lock.try_lock_for(chrono::milliseconds(10))) {
+               return false;
+       }
        if (device->resampling_queue == nullptr) {
                // No buses use this device; throw it away.
-               return;
+               return true;
        }
 
        unsigned num_channels = device->interesting_channels.size();
@@ -223,6 +230,7 @@ void AudioMixer::add_silence(DeviceSpec device_spec, unsigned samples_per_frame,
                // is always the same.
                device->next_local_pts += frame_length;
        }
+       return true;
 }
 
 AudioMixer::AudioDevice *AudioMixer::find_audio_device(DeviceSpec device)
@@ -290,7 +298,7 @@ vector<float> AudioMixer::get_output(double pts, unsigned num_samples, Resamplin
        map<DeviceSpec, vector<float>> samples_card;
        vector<float> samples_bus;
 
-       lock_guard<mutex> lock(audio_mutex);
+       lock_guard<timed_mutex> lock(audio_mutex);
 
        // Pick out all the interesting channels from all the cards.
        // TODO: If the card has been hotswapped, the number of channels
@@ -443,7 +451,7 @@ vector<float> AudioMixer::get_output(double pts, unsigned num_samples, Resamplin
 
 map<DeviceSpec, DeviceInfo> AudioMixer::get_devices() const
 {
-       lock_guard<mutex> lock(audio_mutex);
+       lock_guard<timed_mutex> lock(audio_mutex);
        return get_devices_mutex_held();
 }
 
@@ -473,13 +481,13 @@ void AudioMixer::set_name(DeviceSpec device_spec, const string &name)
 {
        AudioDevice *device = find_audio_device(device_spec);
 
-       lock_guard<mutex> lock(audio_mutex);
+       lock_guard<timed_mutex> lock(audio_mutex);
        device->name = name;
 }
 
 void AudioMixer::set_input_mapping(const InputMapping &new_input_mapping)
 {
-       lock_guard<mutex> lock(audio_mutex);
+       lock_guard<timed_mutex> lock(audio_mutex);
 
        map<DeviceSpec, set<unsigned>> interesting_channels;
        for (const InputMapping::Bus &bus : new_input_mapping.buses) {
@@ -511,6 +519,6 @@ void AudioMixer::set_input_mapping(const InputMapping &new_input_mapping)
 
 InputMapping AudioMixer::get_input_mapping() const
 {
-       lock_guard<mutex> lock(audio_mutex);
+       lock_guard<timed_mutex> lock(audio_mutex);
        return input_mapping;
 }

diff --git a/audio_mixer.h b/audio_mixer.h
index 23b020d43f77bb5765fd14efe55f18b588f6d75d..6e1d5a9458fbb1ef3d808d7cae162591a2ae878d 100644 (file)
--- a/audio_mixer.h
+++ b/audio_mixer.h
@@ -78,9 +78,14 @@ public:
        ~AudioMixer();
        void reset_resampler(DeviceSpec device_spec);
 
-       // frame_length is in TIMEBASE units.
-       void add_audio(DeviceSpec device_spec, const uint8_t *data, unsigned num_samples, bmusb::AudioFormat audio_format, int64_t frame_length);
-       void add_silence(DeviceSpec device_spec, unsigned samples_per_frame, unsigned num_frames, int64_t frame_length);
+       // Add audio (or silence) to the given device's queue. Can return false if
+       // the lock wasn't successfully taken; if so, you should simply try again.
+       // (This is to avoid a deadlock where a card hangs on the mutex in add_audio()
+       // while we are trying to shut it down from another thread that also holds
+       // the mutex.) frame_length is in TIMEBASE units.
+       bool add_audio(DeviceSpec device_spec, const uint8_t *data, unsigned num_samples, bmusb::AudioFormat audio_format, int64_t frame_length);
+       bool add_silence(DeviceSpec device_spec, unsigned samples_per_frame, unsigned num_frames, int64_t frame_length);
+
        std::vector<float> get_output(double pts, unsigned num_samples, ResamplingQueue::RateAdjustmentPolicy rate_adjustment_policy);
 
        // See comments inside get_output().
@@ -219,7 +224,7 @@ private:
 
        unsigned num_cards;
 
-       mutable std::mutex audio_mutex;
+       mutable std::timed_mutex audio_mutex;
 
        AudioDevice video_cards[MAX_VIDEO_CARDS];  // Under audio_mutex.
 

diff --git a/mixer.cpp b/mixer.cpp
index 9eed47ea8f33414f97e6ec3482f164b7c99da5be..38578f90ea7b85609531a63d5bc1bc3806a983b7 100644 (file)
--- a/mixer.cpp
+++ b/mixer.cpp
@@ -391,7 +391,10 @@ void Mixer::bm_frame(unsigned card_index, uint16_t timecode,
                fprintf(stderr, "Card %d dropped %d frame(s) (before timecode 0x%04x), inserting silence.\n",
                        card_index, dropped_frames, timecode);
 
-               audio_mixer.add_silence(device, silence_samples, dropped_frames, frame_length);
+               bool success;
+               do {
+                       success = audio_mixer.add_silence(device, silence_samples, dropped_frames, frame_length);
+               } while (!success);
        }
 
        audio_mixer.add_audio(device, audio_frame.data + audio_offset, num_samples, audio_format, frame_length);