Refactor ALSA code in preparation for hotplug.

[nageru] / alsa_input.h

#ifndef _ALSA_INPUT_H
#define _ALSA_INPUT_H 1

// ALSA sound input, running in a separate thread and sending audio back
// in callbacks.
//
// Note: “frame” here generally refers to the ALSA definition of frame,
// which is a set of samples, exactly one for each channel. The only exception
// is in frame_length, where it means the TIMEBASE length of the buffer
// as a whole, since that's what AudioMixer::add_audio() wants.

#include <alsa/asoundlib.h>

#include <atomic>
#include <functional>
#include <string>
#include <thread>
#include <vector>

#include "bmusb/bmusb.h"
#include "timebase.h"

class ALSAInput {
public:
        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();

        // NOTE: Might very well be different from the sample rate given to the
        // constructor, since the card might not support the one you wanted.
        unsigned get_sample_rate() const { return sample_rate; }

        void start_capture_thread();
        void stop_capture_thread();

private:
        void capture_thread_func();
        int64_t frames_to_pts(uint64_t n) const;
        void die_on_error(const char *func_name, int err);

        std::string device;
        unsigned sample_rate, num_channels, num_periods;
        snd_pcm_uframes_t period_size;
        snd_pcm_uframes_t buffer_frames;
        bmusb::AudioFormat audio_format;
        audio_callback_t audio_callback;

        snd_pcm_t *pcm_handle;
        std::thread capture_thread;
        std::atomic<bool> should_quit{false};
        std::unique_ptr<uint8_t[]> buffer;
};

// The class dealing with the collective of all ALSA cards in the system.
// In particular, it deals with enumeration of cards, and hotplug of new ones.
class ALSAPool {
public:
        ~ALSAPool();

        struct Device {
                enum class State {
                        // There is no card here. (There probably used to be one,
                        // but it got removed.) We don't insert a card before
                        // we've actually probed it, ie., we know whether it
                        // can be captured from at all, and what its name is.
                        EMPTY,

                        // This card is ready for capture, as far as we know.
                        // (It could still be used by someone else; we don't know
                        // until we try to open it.)
                        READY,

                        // We are trying to start capture from this card, but we are not
                        // streaming yet. Note that this could in theory go on forever,
                        // if the card is in use by some other process; in the UI,
                        // we will show this state as “(busy)”.
                        STARTING,

                        // The card is capturing and sending data. If there's a fatal error,
                        // it could go back to STARTING, or it could go to DEAD
                        // (depending on the error).
                        RUNNING,

                        // The card is gone (e.g., unplugged). However, since there's
                        // still a bus using it, we can't just remove the entry.
                        // If the card comes back (ie., a new card is plugged in,
                        // and we believe it has the same configuration), it could be
                        // installed in place of this card, and then presumably be put
                        // back into STARTING or RUNNING.
                        DEAD
                } state;

                std::string address;  // E.g. “hw:0,0”.
                std::string name, info;
                unsigned num_channels;
                ALSAInput *input = nullptr;  // nullptr iff EMPTY or DEAD.

                // Whether the AudioMixer is interested in this card or not.
                // “Interested” could mean either of two things: Either it is part of
                // a bus mapping, or it is in the process of enumerating devices
                // (to show to the user). A card that is _not_ held can disappear
                // at any given time as a result of an error or hotplug event;
                // a card that is held will go to the DEAD state instead.
                bool held = false;
        };

        void init();

        // Get the list of all current devices. Note that this will implicitly mark
        // all of the returned devices as held, since the input mapping UI needs
        // some kind of stability when the user is to choose. Thus, when you are done
        // with the list and have set a new mapping, you must go through all the devices
        // you don't want and release them using release_device().
        std::vector<Device> get_devices();

        void hold_device(unsigned index);
        void release_device(unsigned index);  // Note: index is allowed to go out of bounds.

        // If device is held, start or restart capture. If device is not held,
        // stop capture if it isn't already.
        void reset_device(unsigned index);

        // Note: The card must be held. Returns OUTPUT_FREQUENCY if the card is in EMPTY or DEAD.
        unsigned get_capture_frequency(unsigned index);

        // TODO: Add accessors and/or callbacks about changed state, so that
        // the UI actually stands a chance in using that information.

private:
        mutable std::mutex mu;
        std::vector<Device> devices;  // Under mu.
        std::vector<std::unique_ptr<ALSAInput>> inputs;  // Under mu, corresponds 1:1 to devices.

        void enumerate_devices();
        bool add_device(unsigned card_index, unsigned dev_index);
};

#endif  // !defined(_ALSA_INPUT_H)