cpal/src/alsa/mod.rs

extern crate alsa_sys as alsa;
extern crate libc;

pub use self::enumerate::{EndpointsIterator, default_endpoint};

use ChannelsCount;
use CreationError;
use Format;
use FormatsEnumerationError;
use SampleFormat;
use SamplesRate;
use SupportedFormat;
use UnknownTypeBuffer;

use std::{cmp, ffi, iter, mem, ptr};
use std::sync::Mutex;
use std::sync::atomic::{AtomicUsize, Ordering};
use std::vec::IntoIter as VecIntoIter;

pub type SupportedFormatsIterator = VecIntoIter<SupportedFormat>;

mod enumerate;


struct Trigger {
    // [read fd, write fd]
    fds: [libc::c_int; 2],
}

impl Trigger {
    fn new() -> Self {
        let mut fds = [0, 0];
        match unsafe { libc::pipe(fds.as_mut_ptr()) } {
            0 => Trigger { fds: fds },
            _ => panic!("Could not create pipe"),
        }
    }
    fn read_fd(&self) -> libc::c_int {
        self.fds[0]
    }
    fn write_fd(&self) -> libc::c_int {
        self.fds[1]
    }
    fn wakeup(&self) {
        let buf = 1u64;
        let ret = unsafe { libc::write(self.write_fd(), &buf as *const u64 as *const _, 8) };
        assert!(ret == 8);
    }
    fn clear_pipe(&self) {
        let mut out = 0u64;
        let ret = unsafe { libc::read(self.read_fd(), &mut out as *mut u64 as *mut _, 8) };
        assert_eq!(ret, 8);
    }
}

impl Drop for Trigger {
    fn drop(&mut self) {
        unsafe {
            libc::close(self.fds[0]);
            libc::close(self.fds[1]);
        }
    }
}


#[derive(Clone, Debug, PartialEq, Eq)]
pub struct Endpoint(String);

impl Endpoint {
    pub fn supported_formats(&self) -> Result<SupportedFormatsIterator, FormatsEnumerationError> {
        unsafe {
            let mut playback_handle = mem::uninitialized();
            let device_name = ffi::CString::new(self.0.clone()).expect("Unable to get device name");

            match alsa::snd_pcm_open(&mut playback_handle, device_name.as_ptr() as *const _,
                                     alsa::SND_PCM_STREAM_PLAYBACK, alsa::SND_PCM_NONBLOCK)
            {
                -2 |
                -16 /* determined empirically */ => return Err(FormatsEnumerationError::DeviceNotAvailable),
                e => check_errors(e).expect("device not available")
            }

            let hw_params = HwParams::alloc();
            match check_errors(alsa::snd_pcm_hw_params_any(playback_handle, hw_params.0)) {
                Err(_) => return Ok(Vec::new().into_iter()),
                Ok(_) => (),
            };

            // TODO: check endianess
            const FORMATS: [(SampleFormat, alsa::snd_pcm_format_t); 3] =
                [
                    //SND_PCM_FORMAT_S8,
                    //SND_PCM_FORMAT_U8,
                    (SampleFormat::I16, alsa::SND_PCM_FORMAT_S16_LE),
                    //SND_PCM_FORMAT_S16_BE,
                    (SampleFormat::U16, alsa::SND_PCM_FORMAT_U16_LE),
                    //SND_PCM_FORMAT_U16_BE,
                /*SND_PCM_FORMAT_S24_LE,
                SND_PCM_FORMAT_S24_BE,
                SND_PCM_FORMAT_U24_LE,
                SND_PCM_FORMAT_U24_BE,
                SND_PCM_FORMAT_S32_LE,
                SND_PCM_FORMAT_S32_BE,
                SND_PCM_FORMAT_U32_LE,
                SND_PCM_FORMAT_U32_BE,*/
                    (SampleFormat::F32, alsa::SND_PCM_FORMAT_FLOAT_LE) /*SND_PCM_FORMAT_FLOAT_BE,
                SND_PCM_FORMAT_FLOAT64_LE,
                SND_PCM_FORMAT_FLOAT64_BE,
                SND_PCM_FORMAT_IEC958_SUBFRAME_LE,
                SND_PCM_FORMAT_IEC958_SUBFRAME_BE,
                SND_PCM_FORMAT_MU_LAW,
                SND_PCM_FORMAT_A_LAW,
                SND_PCM_FORMAT_IMA_ADPCM,
                SND_PCM_FORMAT_MPEG,
                SND_PCM_FORMAT_GSM,
                SND_PCM_FORMAT_SPECIAL,
                SND_PCM_FORMAT_S24_3LE,
                SND_PCM_FORMAT_S24_3BE,
                SND_PCM_FORMAT_U24_3LE,
                SND_PCM_FORMAT_U24_3BE,
                SND_PCM_FORMAT_S20_3LE,
                SND_PCM_FORMAT_S20_3BE,
                SND_PCM_FORMAT_U20_3LE,
                SND_PCM_FORMAT_U20_3BE,
                SND_PCM_FORMAT_S18_3LE,
                SND_PCM_FORMAT_S18_3BE,
                SND_PCM_FORMAT_U18_3LE,
                SND_PCM_FORMAT_U18_3BE,*/,
                ];

            let mut supported_formats = Vec::new();
            for &(sample_format, alsa_format) in FORMATS.iter() {
                if alsa::snd_pcm_hw_params_test_format(playback_handle,
                                                       hw_params.0,
                                                       alsa_format) == 0
                {
                    supported_formats.push(sample_format);
                }
            }

            let mut min_rate = mem::uninitialized();
            check_errors(alsa::snd_pcm_hw_params_get_rate_min(hw_params.0,
                                                              &mut min_rate,
                                                              ptr::null_mut()))
                .expect("unable to get minimum supported rete");
            let mut max_rate = mem::uninitialized();
            check_errors(alsa::snd_pcm_hw_params_get_rate_max(hw_params.0,
                                                              &mut max_rate,
                                                              ptr::null_mut()))
                .expect("unable to get maximum supported rate");

            let samples_rates = if min_rate == max_rate {
                vec![(min_rate, max_rate)]
            } else if alsa::snd_pcm_hw_params_test_rate(playback_handle,
                                                        hw_params.0,
                                                        min_rate + 1,
                                                        0) == 0
            {
                vec![(min_rate, max_rate)]
            } else {
                const RATES: [libc::c_uint; 13] = [
                    5512,
                    8000,
                    11025,
                    16000,
                    22050,
                    32000,
                    44100,
                    48000,
                    64000,
                    88200,
                    96000,
                    176400,
                    192000,
                ];

                let mut rates = Vec::new();
                for &rate in RATES.iter() {
                    if alsa::snd_pcm_hw_params_test_rate(playback_handle,
                                                         hw_params.0,
                                                         rate,
                                                         0) == 0
                    {
                        rates.push((rate, rate));
                    }
                }

                if rates.len() == 0 {
                    vec![(min_rate, max_rate)]
                } else {
                    rates
                }
            };

            let mut min_channels = mem::uninitialized();
            check_errors(alsa::snd_pcm_hw_params_get_channels_min(hw_params.0, &mut min_channels))
                .expect("unable to get minimum supported channel count");
            let mut max_channels = mem::uninitialized();
            check_errors(alsa::snd_pcm_hw_params_get_channels_max(hw_params.0, &mut max_channels))
                .expect("unable to get maximum supported channel count");
            let max_channels = cmp::min(max_channels, 32); // TODO: limiting to 32 channels or too much stuff is returned
            let supported_channels = (min_channels .. max_channels + 1)
                .filter_map(|num| if alsa::snd_pcm_hw_params_test_channels(
                    playback_handle,
                    hw_params.0,
                    num,
                ) == 0
                {
                    Some(num as ChannelsCount)
                } else {
                    None
                })
                .collect::<Vec<_>>();

            let mut output = Vec::with_capacity(supported_formats.len() * supported_channels.len() *
                                                    samples_rates.len());
            for &data_type in supported_formats.iter() {
                for channels in supported_channels.iter() {
                    for &(min_rate, max_rate) in samples_rates.iter() {
                        output.push(SupportedFormat {
                                        channels: channels.clone(),
                                        min_samples_rate: SamplesRate(min_rate as u32),
                                        max_samples_rate: SamplesRate(max_rate as u32),
                                        data_type: data_type,
                                    });
                    }
                }
            }

            // TODO: RAII
            alsa::snd_pcm_close(playback_handle);
            Ok(output.into_iter())
        }
    }

    #[inline]
    pub fn name(&self) -> String {
        self.0.clone()
    }
}

pub struct EventLoop {
    // Each newly-created voice gets a new ID from this counter. The counter is then incremented.
    next_voice_id: AtomicUsize, // TODO: use AtomicU64 when stable?

    // A trigger that uses a `pipe()` as backend. Signalled whenever a new command is ready, so
    // that `poll()` can wake up and pick the changes.
    pending_trigger: Trigger,

    // This field is locked by the `run()` method.
    // The mutex also ensures that only one thread at a time has `run()` running.
    run_context: Mutex<RunContext>,

    // Commands processed by the `run()` method that is currently running.
    // TODO: use a lock-free container
    commands: Mutex<Vec<Command>>,
}

unsafe impl Send for EventLoop {
}

unsafe impl Sync for EventLoop {
}

enum Command {
    NewVoice(VoiceInner),
    PlayVoice(VoiceId),
    PauseVoice(VoiceId),
    DestroyVoice(VoiceId),
}

struct RunContext {
    // Descriptors to wait for. Always contains `pending_trigger.read_fd()` as first element.
    descriptors: Vec<libc::pollfd>,
    // List of voices that are written in `descriptors`.
    voices: Vec<VoiceInner>,
}

struct VoiceInner {
    // The id of the voice.
    id: VoiceId,

    // The ALSA channel.
    channel: *mut alsa::snd_pcm_t,

    // When converting between file descriptors and `snd_pcm_t`, this is the number of
    // file descriptors that this `snd_pcm_t` uses.
    num_descriptors: usize,

    // Format of the samples.
    sample_format: SampleFormat,

    // Number of channels, ie. number of samples per frame.
    num_channels: u16,

    // Number of samples that can fit in the buffer.
    buffer_len: usize,

    // Minimum number of samples to put in the buffer.
    period_len: usize,

    // Whether or not the hardware supports pausing the stream.
    can_pause: bool,

    // Whether or not the sample stream is currently paused.
    is_paused: bool,

    // A file descriptor opened with `eventfd`.
    // It is used to wait for resume signal.
    resume_trigger: Trigger,
}

#[derive(Debug, Clone, PartialEq, Eq, Hash)]
pub struct VoiceId(usize);

impl EventLoop {
    #[inline]
    pub fn new() -> EventLoop {
        let pending_trigger = Trigger::new();

        let initial_descriptors = vec![
            libc::pollfd {
                fd: pending_trigger.read_fd(),
                events: libc::POLLIN,
                revents: 0,
            },
        ];

        let run_context = Mutex::new(RunContext {
                                         descriptors: initial_descriptors,
                                         voices: Vec::new(),
                                     });

        EventLoop {
            next_voice_id: AtomicUsize::new(0),
            pending_trigger: pending_trigger,
            run_context,
            commands: Mutex::new(Vec::new()),
        }
    }

    #[inline]
    pub fn run<F>(&self, mut callback: F) -> !
        where F: FnMut(VoiceId, UnknownTypeBuffer)
    {
        self.run_inner(&mut callback)
    }

    fn run_inner(&self, callback: &mut FnMut(VoiceId, UnknownTypeBuffer)) -> ! {
        unsafe {
            let mut run_context = self.run_context.lock().unwrap();
            let run_context = &mut *run_context;

            loop {
                {
                    let mut commands_lock = self.commands.lock().unwrap();
                    if !commands_lock.is_empty() {
                        for command in commands_lock.drain(..) {
                            match command {
                                Command::DestroyVoice(voice_id) => {
                                    run_context.voices.retain(|v| v.id != voice_id);
                                },
                                Command::PlayVoice(voice_id) => {
                                    if let Some(voice) = run_context.voices.iter_mut()
                                        .find(|voice| voice.can_pause && voice.id == voice_id)
                                    {
                                        alsa::snd_pcm_pause(voice.channel, 0);
                                        voice.is_paused = false;
                                    }
                                },
                                Command::PauseVoice(voice_id) => {
                                    if let Some(voice) = run_context.voices.iter_mut()
                                        .find(|voice| voice.can_pause && voice.id == voice_id)
                                    {
                                        alsa::snd_pcm_pause(voice.channel, 1);
                                        voice.is_paused = true;
                                    }
                                },
                                Command::NewVoice(voice_inner) => {
                                    run_context.voices.push(voice_inner);
                                },
                            }
                        }

                        run_context.descriptors = vec![
                            libc::pollfd {
                                fd: self.pending_trigger.read_fd(),
                                events: libc::POLLIN,
                                revents: 0,
                            },
                        ];
                        for voice in run_context.voices.iter() {
                            run_context.descriptors.reserve(voice.num_descriptors);
                            let len = run_context.descriptors.len();
                            let filled = alsa::snd_pcm_poll_descriptors(voice.channel,
                                                                        run_context
                                                                            .descriptors
                                                                            .as_mut_ptr()
                                                                            .offset(len as isize),
                                                                        voice.num_descriptors as
                                                                            libc::c_uint);
                            debug_assert_eq!(filled, voice.num_descriptors as libc::c_int);
                            run_context.descriptors.set_len(len + voice.num_descriptors);
                        }
                    }
                }

                let ret = libc::poll(run_context.descriptors.as_mut_ptr(),
                                     run_context.descriptors.len() as libc::nfds_t,
                                     -1 /* infinite */);
                assert!(ret >= 0, "poll() failed");

                if ret == 0 {
                    continue;
                }

                // If the `pending_trigger` was signaled, we need to process the comands.
                if run_context.descriptors[0].revents != 0 {
                    run_context.descriptors[0].revents = 0;
                    self.pending_trigger.clear_pipe();
                }

                // Iterate over each individual voice/descriptor.
                let mut i_voice = 0;
                let mut i_descriptor = 1;
                while (i_descriptor as usize) < run_context.descriptors.len() {
                    let voice_inner = run_context.voices.get_mut(i_voice).unwrap();

                    // Check whether the event is `POLLOUT`. If not, `continue`.
                    {
                        let mut revent = mem::uninitialized();

                        {
                            let num_descriptors = voice_inner.num_descriptors as libc::c_uint;
                            let desc_ptr =
                                run_context.descriptors.as_mut_ptr().offset(i_descriptor);
                            let res = alsa::snd_pcm_poll_descriptors_revents(voice_inner.channel,
                                                                             desc_ptr,
                                                                             num_descriptors,
                                                                             &mut revent);
                            check_errors(res).unwrap();
                        }

                        if (revent as libc::c_short & libc::POLLOUT) == 0 {
                            i_descriptor += voice_inner.num_descriptors as isize;
                            i_voice += 1;
                            continue;
                        }
                    }

                    // Determine the number of samples that are available to write.
                    let available = {
                        let available = alsa::snd_pcm_avail(voice_inner.channel); // TODO: what about snd_pcm_avail_update?

                        if available == -32 {
                            // buffer underrun
                            voice_inner.buffer_len
                        } else if available < 0 {
                            check_errors(available as libc::c_int)
                                .expect("buffer is not available");
                            unreachable!()
                        } else {
                            (available * voice_inner.num_channels as alsa::snd_pcm_sframes_t) as
                                usize
                        }
                    };

                    if available < voice_inner.period_len {
                        i_descriptor += voice_inner.num_descriptors as isize;
                        i_voice += 1;
                        continue;
                    }

                    let voice_id = voice_inner.id.clone();

                    // We're now sure that we're ready to write data.
                    let buffer = match voice_inner.sample_format {
                        SampleFormat::I16 => {
                            let buffer = Buffer {
                                voice_inner: voice_inner,
                                buffer: iter::repeat(mem::uninitialized())
                                    .take(available)
                                    .collect(),
                            };

                            UnknownTypeBuffer::I16(::Buffer { target: Some(buffer) })
                        },
                        SampleFormat::U16 => {
                            let buffer = Buffer {
                                voice_inner: voice_inner,
                                buffer: iter::repeat(mem::uninitialized())
                                    .take(available)
                                    .collect(),
                            };

                            UnknownTypeBuffer::U16(::Buffer { target: Some(buffer) })
                        },
                        SampleFormat::F32 => {
                            let buffer = Buffer {
                                voice_inner: voice_inner,
                                // Note that we don't use `mem::uninitialized` because of sNaN.
                                buffer: iter::repeat(0.0).take(available).collect(),
                            };

                            UnknownTypeBuffer::F32(::Buffer { target: Some(buffer) })
                        },
                    };

                    callback(voice_id, buffer);
                }
            }
        }
    }

    pub fn build_voice(&self, endpoint: &Endpoint, format: &Format)
                       -> Result<VoiceId, CreationError> {
        unsafe {
            let name = ffi::CString::new(endpoint.0.clone()).expect("unable to clone endpoint");

            let mut playback_handle = mem::uninitialized();
            match alsa::snd_pcm_open(&mut playback_handle, name.as_ptr(),
                                     alsa::SND_PCM_STREAM_PLAYBACK, 0)
            {
                -16 /* determined empirically */ => return Err(CreationError::DeviceNotAvailable),
                e => check_errors(e).expect("Device unavailable")
            }

            let data_type = if cfg!(target_endian = "big") {
                match format.data_type {
                    SampleFormat::I16 => alsa::SND_PCM_FORMAT_S16_BE,
                    SampleFormat::U16 => alsa::SND_PCM_FORMAT_U16_BE,
                    SampleFormat::F32 => alsa::SND_PCM_FORMAT_FLOAT_BE,
                }
            } else {
                match format.data_type {
                    SampleFormat::I16 => alsa::SND_PCM_FORMAT_S16_LE,
                    SampleFormat::U16 => alsa::SND_PCM_FORMAT_U16_LE,
                    SampleFormat::F32 => alsa::SND_PCM_FORMAT_FLOAT_LE,
                }
            };

            let hw_params = HwParams::alloc();
            check_errors(alsa::snd_pcm_hw_params_any(playback_handle, hw_params.0))
                .expect("Errors on playback handle");
            check_errors(alsa::snd_pcm_hw_params_set_access(playback_handle,
                                                            hw_params.0,
                                                            alsa::SND_PCM_ACCESS_RW_INTERLEAVED))
                .expect("handle not acessible");
            check_errors(alsa::snd_pcm_hw_params_set_format(playback_handle,
                                                            hw_params.0,
                                                            data_type))
                .expect("format could not be set");
            check_errors(alsa::snd_pcm_hw_params_set_rate(playback_handle,
                                                          hw_params.0,
                                                          format.samples_rate.0 as libc::c_uint,
                                                          0))
                .expect("sample rate could not be set");
            check_errors(alsa::snd_pcm_hw_params_set_channels(playback_handle,
                                                              hw_params.0,
                                                              format.channels as
                                                                  libc::c_uint))
                .expect("channel count could not be set");
            let mut max_buffer_size = format.samples_rate.0 as alsa::snd_pcm_uframes_t /
                format.channels as alsa::snd_pcm_uframes_t /
                5; // 200ms of buffer
            check_errors(alsa::snd_pcm_hw_params_set_buffer_size_max(playback_handle,
                                                                     hw_params.0,
                                                                     &mut max_buffer_size))
                .unwrap();
            check_errors(alsa::snd_pcm_hw_params(playback_handle, hw_params.0))
                .expect("hardware params could not be set");

            let can_pause = alsa::snd_pcm_hw_params_can_pause(hw_params.0) == 1;

            let mut sw_params = mem::uninitialized(); // TODO: RAII
            check_errors(alsa::snd_pcm_sw_params_malloc(&mut sw_params)).unwrap();
            check_errors(alsa::snd_pcm_sw_params_current(playback_handle, sw_params)).unwrap();
            check_errors(alsa::snd_pcm_sw_params_set_start_threshold(playback_handle,
                                                                     sw_params,
                                                                     0))
                .unwrap();

            let (buffer_len, period_len) = {
                let mut buffer = mem::uninitialized();
                let mut period = mem::uninitialized();
                check_errors(alsa::snd_pcm_get_params(playback_handle, &mut buffer, &mut period))
                    .expect("could not initialize buffer");
                assert!(buffer != 0);
                check_errors(alsa::snd_pcm_sw_params_set_avail_min(playback_handle,
                                                                   sw_params,
                                                                   period))
                    .unwrap();
                let buffer = buffer as usize * format.channels as usize;
                let period = period as usize * format.channels as usize;
                (buffer, period)
            };

            check_errors(alsa::snd_pcm_sw_params(playback_handle, sw_params)).unwrap();
            check_errors(alsa::snd_pcm_prepare(playback_handle))
                .expect("could not get playback handle");

            let num_descriptors = {
                let num_descriptors = alsa::snd_pcm_poll_descriptors_count(playback_handle);
                debug_assert!(num_descriptors >= 1);
                num_descriptors as usize
            };

            let new_voice_id = VoiceId(self.next_voice_id.fetch_add(1, Ordering::Relaxed));
            assert_ne!(new_voice_id.0, usize::max_value()); // check for overflows

            let voice_inner = VoiceInner {
                id: new_voice_id.clone(),
                channel: playback_handle,
                sample_format: format.data_type,
                num_descriptors: num_descriptors,
                num_channels: format.channels as u16,
                buffer_len: buffer_len,
                period_len: period_len,
                can_pause: can_pause,
                is_paused: false,
                resume_trigger: Trigger::new(),
            };

            self.push_command(Command::NewVoice(voice_inner));
            Ok(new_voice_id)
        }
    }

    #[inline]
    fn push_command(&self, command: Command) {
        self.commands.lock().unwrap().push(command);
        self.pending_trigger.wakeup();
    }

    #[inline]
    pub fn destroy_voice(&self, voice_id: VoiceId) {
        self.push_command(Command::DestroyVoice(voice_id));
    }

    #[inline]
    pub fn play(&self, voice_id: VoiceId) {
        self.push_command(Command::PlayVoice(voice_id));
    }

    #[inline]
    pub fn pause(&self, voice_id: VoiceId) {
        self.push_command(Command::PauseVoice(voice_id));
    }
}

pub struct Buffer<'a, T: 'a> {
    voice_inner: &'a mut VoiceInner,
    buffer: Vec<T>,
}

/// Wrapper around `hw_params`.
struct HwParams(*mut alsa::snd_pcm_hw_params_t);

impl HwParams {
    pub fn alloc() -> HwParams {
        unsafe {
            let mut hw_params = mem::uninitialized();
            check_errors(alsa::snd_pcm_hw_params_malloc(&mut hw_params))
                .expect("unable to get hardware parameters");
            HwParams(hw_params)
        }
    }
}

impl Drop for HwParams {
    fn drop(&mut self) {
        unsafe {
            alsa::snd_pcm_hw_params_free(self.0);
        }
    }
}

impl Drop for VoiceInner {
    #[inline]
    fn drop(&mut self) {
        unsafe {
            alsa::snd_pcm_close(self.channel);
        }
    }
}

impl<'a, T> Buffer<'a, T> {
    #[inline]
    pub fn buffer(&mut self) -> &mut [T] {
        &mut self.buffer
    }

    #[inline]
    pub fn len(&self) -> usize {
        self.buffer.len()
    }

    pub fn finish(self) {
        let to_write = (self.buffer.len() / self.voice_inner.num_channels as usize) as
            alsa::snd_pcm_uframes_t;

        unsafe {
            loop {
                let result = alsa::snd_pcm_writei(self.voice_inner.channel,
                                                  self.buffer.as_ptr() as *const _,
                                                  to_write);

                if result == -32 {
                    // buffer underrun
                    alsa::snd_pcm_prepare(self.voice_inner.channel);
                } else if result < 0 {
                    check_errors(result as libc::c_int).expect("could not write pcm");
                } else {
                    assert_eq!(result as alsa::snd_pcm_uframes_t, to_write);
                    break;
                }
            }
        }
    }
}

#[inline]
fn check_errors(err: libc::c_int) -> Result<(), String> {
    use std::ffi;

    if err < 0 {
        unsafe {
            let s = ffi::CStr::from_ptr(alsa::snd_strerror(err))
                .to_bytes()
                .to_vec();
            let s = String::from_utf8(s).expect("Streaming error occured");
            return Err(s);
        }
    }

    Ok(())
}