gst-plugins-rs/gst-plugin-threadshare/src/queue.rs

// Copyright (C) 2018 Sebastian Dröge <sebastian@centricular.com>
//
// This library is free software; you can redistribute it and/or
// modify it under the terms of the GNU Library General Public
// License as published by the Free Software Foundation; either
// version 2 of the License, or (at your option) any later version.
//
// This library is distributed in the hope that it will be useful,
// but WITHOUT ANY WARRANTY; without even the implied warranty of
// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
// Library General Public License for more details.
//
// You should have received a copy of the GNU Library General Public
// License along with this library; if not, write to the
// Free Software Foundation, Inc., 51 Franklin Street, Suite 500,
// Boston, MA 02110-1335, USA.

use glib;
use glib::prelude::*;
use gst;
use gst::prelude::*;

use gst_plugin::properties::*;
use gst_plugin::object::*;
use gst_plugin::element::*;

use std::sync::{Arc, Mutex};
use std::{u16, u32, u64};
use std::collections::VecDeque;

use futures::{Async, Future, IntoFuture, Poll, Stream};
use futures::task;
use futures::sync::oneshot;

use iocontext::*;

const DEFAULT_MAX_SIZE_BUFFERS: u32 = 200;
const DEFAULT_MAX_SIZE_BYTES: u32 = 1024 * 1024;
const DEFAULT_MAX_SIZE_TIME: u64 = gst::SECOND_VAL;
const DEFAULT_CONTEXT: &'static str = "";
const DEFAULT_CONTEXT_THREADS: i32 = 0;
const DEFAULT_CONTEXT_WAIT: u32 = 0;

#[derive(Debug, Clone)]
struct Settings {
    max_size_buffers: u32,
    max_size_bytes: u32,
    max_size_time: u64,
    context: String,
    context_threads: i32,
    context_wait: u32,
}

impl Default for Settings {
    fn default() -> Self {
        Settings {
            max_size_buffers: DEFAULT_MAX_SIZE_BUFFERS,
            max_size_bytes: DEFAULT_MAX_SIZE_BYTES,
            max_size_time: DEFAULT_MAX_SIZE_TIME,
            context: DEFAULT_CONTEXT.into(),
            context_threads: DEFAULT_CONTEXT_THREADS,
            context_wait: DEFAULT_CONTEXT_WAIT,
        }
    }
}

static PROPERTIES: [Property; 6] = [
    Property::UInt(
        "max-size-buffers",
        "Max Size Buffers",
        "Maximum number of buffers to queue (0=unlimited)",
        (0, u32::MAX),
        DEFAULT_MAX_SIZE_BUFFERS,
        PropertyMutability::ReadWrite,
    ),
    Property::UInt(
        "max-size-bytes",
        "Max Size Bytes",
        "Maximum number of bytes to queue (0=unlimited)",
        (0, u32::MAX),
        DEFAULT_MAX_SIZE_BYTES,
        PropertyMutability::ReadWrite,
    ),
    Property::UInt64(
        "max-size-time",
        "Max Size Time",
        "Maximum number of nanoseconds to queue (0=unlimited)",
        (0, u64::MAX - 1),
        DEFAULT_MAX_SIZE_TIME,
        PropertyMutability::ReadWrite,
    ),
    Property::String(
        "context",
        "Context",
        "Context name to share threads with",
        Some(DEFAULT_CONTEXT),
        PropertyMutability::ReadWrite,
    ),
    Property::Int(
        "context-threads",
        "Context Threads",
        "Number of threads for the context thread-pool if we create it",
        (-1, u16::MAX as i32),
        DEFAULT_CONTEXT_THREADS,
        PropertyMutability::ReadWrite,
    ),
    Property::UInt(
        "context-wait",
        "Context Wait",
        "Throttle poll loop to run at most once every this many ms",
        (0, 1000),
        DEFAULT_CONTEXT_WAIT,
        PropertyMutability::ReadWrite,
    ),
];

lazy_static!{
    static ref DATA_QUEUE_CAT: gst::DebugCategory = gst::DebugCategory::new(
                "ts-dataqueue",
                gst::DebugColorFlags::empty(),
                "Thread-sharing queue",
            );
}

#[derive(Debug)]
enum DataQueueItem {
    Buffer(gst::Buffer),
    BufferList(gst::BufferList),
    Event(gst::Event),
}

impl DataQueueItem {
    fn size(&self) -> (u32, u32) {
        match *self {
            DataQueueItem::Buffer(ref buffer) => (1, buffer.get_size() as u32),
            DataQueueItem::BufferList(ref list) => (
                list.len() as u32,
                list.iter().map(|b| b.get_size() as u32).sum::<u32>(),
            ),
            DataQueueItem::Event(_) => (0, 0),
        }
    }

    fn timestamp(&self) -> Option<u64> {
        match *self {
            DataQueueItem::Buffer(ref buffer) => buffer.get_dts_or_pts().0,
            DataQueueItem::BufferList(ref list) => {
                list.iter().filter_map(|b| b.get_dts_or_pts().0).next()
            }
            DataQueueItem::Event(_) => None,
        }
    }

    fn timestamp_end(&self) -> Option<u64> {
        match *self {
            DataQueueItem::Buffer(ref buffer) => buffer
                .get_dts_or_pts()
                .map(|ts| ts + buffer.get_duration().unwrap_or(0)),
            DataQueueItem::BufferList(ref list) => list.iter()
                .filter_map(|b| {
                    b.get_dts_or_pts()
                        .map(|ts| (ts + b.get_duration().unwrap_or(0)))
                })
                .last(),
            DataQueueItem::Event(_) => None,
        }
    }
}

#[derive(PartialEq, Eq, Debug)]
enum DataQueueState {
    Unscheduled,
    Scheduled,
    Running,
    Shutdown,
}

#[derive(Clone)]
struct DataQueue(Arc<Mutex<DataQueueInner>>);

struct DataQueueInner {
    element: gst::Element,

    state: DataQueueState,
    queue: VecDeque<DataQueueItem>,

    cur_size_buffers: u32,
    cur_size_bytes: u32,
    max_size_buffers: Option<u32>,
    max_size_bytes: Option<u32>,
    max_size_time: Option<u64>,

    current_task: Option<task::Task>,
    current_task_in: Option<task::Task>,
    shutdown_receiver: Option<oneshot::Receiver<()>>,
}

impl DataQueue {
    fn new(element: &gst::Element, settings: &Settings) -> DataQueue {
        DataQueue(Arc::new(Mutex::new(DataQueueInner {
            element: element.clone(),
            state: DataQueueState::Unscheduled,
            queue: VecDeque::new(),
            cur_size_buffers: 0,
            cur_size_bytes: 0,
            max_size_buffers: if settings.max_size_buffers == 0 {
                None
            } else {
                Some(settings.max_size_buffers)
            },
            max_size_bytes: if settings.max_size_bytes == 0 {
                None
            } else {
                Some(settings.max_size_bytes)
            },
            max_size_time: if settings.max_size_time == 0 {
                None
            } else {
                Some(settings.max_size_time)
            },
            current_task: None,
            current_task_in: None,
            shutdown_receiver: None,
        })))
    }

    pub fn schedule<U, F, G>(&self, io_context: &IOContext, func: F, err_func: G) -> Result<(), ()>
    where
        F: Fn(DataQueueItem) -> U + Send + 'static,
        U: IntoFuture<Item = (), Error = gst::FlowError> + 'static,
        <U as IntoFuture>::Future: Send + 'static,
        G: FnOnce(gst::FlowError) + Send + 'static,
    {
        // Ready->Paused
        //
        // Need to wait for a possible shutdown to finish first
        // spawn() on the reactor, change state to Scheduled

        let mut inner = self.0.lock().unwrap();
        gst_debug!(DATA_QUEUE_CAT, obj: &inner.element, "Scheduling data queue");
        if inner.state == DataQueueState::Scheduled {
            gst_debug!(DATA_QUEUE_CAT, obj: &inner.element, "Data queue already scheduled");
            return Ok(());
        }

        assert_eq!(inner.state, DataQueueState::Unscheduled);
        inner.state = DataQueueState::Scheduled;

        let (sender, receiver) = oneshot::channel::<()>();
        inner.shutdown_receiver = Some(receiver);

        let queue_clone = self.clone();
        let element_clone = inner.element.clone();
        io_context.spawn(queue_clone.for_each(func).then(move |res| {
            gst_debug!(
                DATA_QUEUE_CAT,
                obj: &element_clone,
                "Data queue finished: {:?}",
                res
            );

            if let Err(err) = res {
                err_func(err);
            }

            let _ = sender.send(());

            Ok(())
        }));
        Ok(())
    }

    pub fn unpause(&self) {
        // Paused->Playing
        //
        // Change state to Running and signal task
        let mut inner = self.0.lock().unwrap();
        gst_debug!(DATA_QUEUE_CAT, obj: &inner.element, "Unpausing data queue");
        if inner.state == DataQueueState::Running {
            gst_debug!(DATA_QUEUE_CAT, obj: &inner.element, "Data queue already unpaused");
            return;
        }

        assert_eq!(inner.state, DataQueueState::Scheduled);
        inner.state = DataQueueState::Running;

        if let Some(task) = inner.current_task.take() {
            task.notify();
        }
    }

    pub fn pause(&self) {
        // Playing->Paused
        //
        // Change state to Scheduled and signal task

        let mut inner = self.0.lock().unwrap();
        gst_debug!(DATA_QUEUE_CAT, obj: &inner.element, "Pausing data queue");
        if inner.state == DataQueueState::Scheduled {
            gst_debug!(DATA_QUEUE_CAT, obj: &inner.element, "Data queue already paused");
            return;
        }

        assert_eq!(inner.state, DataQueueState::Running);
        inner.state = DataQueueState::Scheduled;

        if let Some(task) = inner.current_task.take() {
            task.notify();
        }
    }

    pub fn shutdown(&self) {
        // Paused->Ready
        //
        // Change state to Shutdown and signal task, wait for our future to be finished
        // Requires scheduled function to be unblocked! Pad must be deactivated before

        let mut inner = self.0.lock().unwrap();
        gst_debug!(DATA_QUEUE_CAT, obj: &inner.element, "Shutting down data queue");
        if inner.state == DataQueueState::Unscheduled {
            gst_debug!(DATA_QUEUE_CAT, obj: &inner.element, "Data queue already shut down");
            return;
        }

        assert!(inner.state == DataQueueState::Scheduled || inner.state == DataQueueState::Running);
        inner.state = DataQueueState::Shutdown;

        if let Some(task) = inner.current_task.take() {
            task.notify();
        }

        let shutdown_receiver = inner.shutdown_receiver.take().unwrap();
        gst_debug!(DATA_QUEUE_CAT, obj: &inner.element, "Waiting for data queue to shut down");
        drop(inner);

        shutdown_receiver.wait().expect("Already shut down");

        let mut inner = self.0.lock().unwrap();
        inner.state = DataQueueState::Unscheduled;
        gst_debug!(DATA_QUEUE_CAT, obj: &inner.element, "Data queue shut down");
    }

    fn clear(&self, src_pad: &gst::Pad) {
        let mut inner = self.0.lock().unwrap();

        gst_debug!(DATA_QUEUE_CAT, obj: &inner.element, "Clearing queue");
        for item in inner.queue.drain(..) {
            if let DataQueueItem::Event(event) = item {
                if event.is_sticky() && event.get_type() != gst::EventType::Segment
                    && event.get_type() != gst::EventType::Eos
                {
                    let _ = src_pad.store_sticky_event(&event);
                }
            }
        }
    }

    fn push(&self, item: DataQueueItem) -> bool {
        let mut inner = self.0.lock().unwrap();

        gst_debug!(DATA_QUEUE_CAT, obj: &inner.element, "Pushing item {:?}", item);

        let (count, bytes) = item.size();
        let ts_end = item.timestamp_end();
        let ts = inner.queue.iter().filter_map(|i| i.timestamp()).next();

        if let Some(max) = inner.max_size_buffers {
            if max <= inner.cur_size_buffers + count {
                gst_debug!(DATA_QUEUE_CAT, obj: &inner.element, "Queue is full (buffers): {} <= {}", max, inner.cur_size_buffers + count);
                inner.current_task_in = Some(task::current());
                return false;
            }
        }

        if let Some(max) = inner.max_size_bytes {
            if max <= inner.cur_size_bytes + bytes {
                gst_debug!(DATA_QUEUE_CAT, obj: &inner.element, "Queue is full (bytes): {} <= {}", max, inner.cur_size_bytes + bytes);
                inner.current_task_in = Some(task::current());
                return false;
            }
        }

        // FIXME: Use running time
        if let (Some(max), Some(ts), Some(ts_end)) = (inner.max_size_time, ts, ts_end) {
            let level = if ts > ts_end {
                ts - ts_end
            } else {
                ts_end - ts
            };
            if max <= level {
                gst_debug!(DATA_QUEUE_CAT, obj: &inner.element, "Queue is full (time): {} <= {}", max, level);
                inner.current_task_in = Some(task::current());
                return false;
            }
        }

        inner.queue.push_back(item);
        inner.cur_size_buffers += count;
        inner.cur_size_bytes += bytes;

        if let Some(task) = inner.current_task.take() {
            task.notify();
        }

        true
    }
}

impl Drop for DataQueueInner {
    fn drop(&mut self) {
        assert_eq!(self.state, DataQueueState::Unscheduled);
    }
}

impl Stream for DataQueue {
    type Item = DataQueueItem;
    type Error = gst::FlowError;

    fn poll(&mut self) -> Poll<Option<Self::Item>, Self::Error> {
        let mut inner = self.0.lock().unwrap();
        if inner.state == DataQueueState::Shutdown {
            gst_debug!(DATA_QUEUE_CAT, obj: &inner.element, "Data queue shutting down");
            return Ok(Async::Ready(None));
        } else if inner.state == DataQueueState::Scheduled {
            gst_debug!(DATA_QUEUE_CAT, obj: &inner.element, "Data queue not running");
            inner.current_task = Some(task::current());
            return Ok(Async::NotReady);
        }

        assert_eq!(inner.state, DataQueueState::Running);

        gst_debug!(DATA_QUEUE_CAT, obj: &inner.element, "Trying to read data");
        match inner.queue.pop_front() {
            None => {
                gst_debug!(DATA_QUEUE_CAT, obj: &inner.element, "Data queue is empty");
                inner.current_task = Some(task::current());
                Ok(Async::NotReady)
            }
            Some(item) => {
                gst_debug!(DATA_QUEUE_CAT, obj: &inner.element, "Popped item {:?}", item);

                let (count, bytes) = item.size();
                inner.cur_size_buffers -= count;
                inner.cur_size_bytes -= bytes;

                if let Some(task) = inner.current_task_in.take() {
                    task.notify();
                }

                Ok(Async::Ready(Some(item)))
            }
        }
    }
}

struct State {
    io_context: Option<IOContext>,
    queue: Option<DataQueue>,
    last_ret: gst::FlowReturn,
}

impl Default for State {
    fn default() -> State {
        State {
            io_context: None,
            queue: None,
            last_ret: gst::FlowReturn::Ok,
        }
    }
}

struct Queue {
    cat: gst::DebugCategory,
    sink_pad: gst::Pad,
    src_pad: gst::Pad,
    state: Mutex<State>,
    settings: Mutex<Settings>,
}

impl Queue {
    fn class_init(klass: &mut ElementClass) {
        klass.set_metadata(
            "Thread-sharing queue",
            "Generic",
            "Simple data queue",
            "Sebastian Dröge <sebastian@centricular.com>",
        );

        let caps = gst::Caps::new_any();

        let sink_pad_template = gst::PadTemplate::new(
            "sink",
            gst::PadDirection::Sink,
            gst::PadPresence::Always,
            &caps,
        );
        klass.add_pad_template(sink_pad_template);

        let src_pad_template = gst::PadTemplate::new(
            "src",
            gst::PadDirection::Src,
            gst::PadPresence::Always,
            &caps,
        );
        klass.add_pad_template(src_pad_template);

        klass.install_properties(&PROPERTIES);
    }

    fn init(element: &Element) -> Box<ElementImpl<Element>> {
        let templ = element.get_pad_template("sink").unwrap();
        let sink_pad = gst::Pad::new_from_template(&templ, "sink");
        let templ = element.get_pad_template("src").unwrap();
        let src_pad = gst::Pad::new_from_template(&templ, "src");

        sink_pad.set_chain_function(|pad, parent, buffer| {
            Queue::catch_panic_pad_function(
                parent,
                || gst::FlowReturn::Error,
                |queue, element| queue.sink_chain(pad, element, buffer),
            )
        });
        sink_pad.set_chain_list_function(|pad, parent, list| {
            Queue::catch_panic_pad_function(
                parent,
                || gst::FlowReturn::Error,
                |queue, element| queue.sink_chain_list(pad, element, list),
            )
        });
        sink_pad.set_event_function(|pad, parent, event| {
            Queue::catch_panic_pad_function(
                parent,
                || false,
                |queue, element| queue.sink_event(pad, element, event),
            )
        });
        sink_pad.set_query_function(|pad, parent, query| {
            Queue::catch_panic_pad_function(
                parent,
                || false,
                |queue, element| queue.sink_query(pad, element, query),
            )
        });

        src_pad.set_event_function(|pad, parent, event| {
            Queue::catch_panic_pad_function(
                parent,
                || false,
                |queue, element| queue.src_event(pad, element, event),
            )
        });
        src_pad.set_query_function(|pad, parent, query| {
            Queue::catch_panic_pad_function(
                parent,
                || false,
                |queue, element| queue.src_query(pad, element, query),
            )
        });
        element.add_pad(&sink_pad).unwrap();
        element.add_pad(&src_pad).unwrap();

        Box::new(Self {
            cat: gst::DebugCategory::new(
                "ts-queue",
                gst::DebugColorFlags::empty(),
                "Thread-sharing queue",
            ),
            sink_pad: sink_pad,
            src_pad: src_pad,
            state: Mutex::new(State::default()),
            settings: Mutex::new(Settings::default()),
        })
    }

    fn catch_panic_pad_function<T, F: FnOnce(&Self, &Element) -> T, G: FnOnce() -> T>(
        parent: &Option<gst::Object>,
        fallback: G,
        f: F,
    ) -> T {
        let element = parent
            .as_ref()
            .cloned()
            .unwrap()
            .downcast::<Element>()
            .unwrap();
        let queue = element.get_impl().downcast_ref::<Queue>().unwrap();
        element.catch_panic(fallback, |element| f(queue, element))
    }

    fn sink_chain(
        &self,
        pad: &gst::Pad,
        _element: &Element,
        buffer: gst::Buffer,
    ) -> gst::FlowReturn {
        gst_log!(self.cat, obj: pad, "Handling buffer {:?}", buffer);

        let state = self.state.lock().unwrap();
        let queue = match state.queue {
            None => return gst::FlowReturn::Error,
            Some(ref queue) => queue,
        };

        queue.push(DataQueueItem::Buffer(buffer));

        state.last_ret
    }

    fn sink_chain_list(
        &self,
        pad: &gst::Pad,
        _element: &Element,
        list: gst::BufferList,
    ) -> gst::FlowReturn {
        gst_log!(self.cat, obj: pad, "Handling buffer list {:?}", list);

        let state = self.state.lock().unwrap();
        let queue = match state.queue {
            None => return gst::FlowReturn::Error,
            Some(ref queue) => queue,
        };

        queue.push(DataQueueItem::BufferList(list));

        state.last_ret
    }

    fn sink_event(&self, pad: &gst::Pad, element: &Element, event: gst::Event) -> bool {
        use gst::EventView;

        gst_log!(self.cat, obj: pad, "Handling event {:?}", event);

        match event.view() {
            EventView::FlushStart(..) => {
                let _ = self.stop(element);
            }
            EventView::FlushStop(..) => {
                let (ret, state, pending) = element.get_state(0.into());
                if ret == gst::StateChangeReturn::Success && state == gst::State::Paused
                    || ret == gst::StateChangeReturn::Async && pending == gst::State::Paused
                {
                    let _ = self.start(element);
                }
            }
            _ => (),
        };

        if event.is_serialized() {
            gst_log!(self.cat, obj: pad, "Queuing event {:?}", event);
            let state = self.state.lock().unwrap();
            state
                .queue
                .as_ref()
                .map(|q| q.push(DataQueueItem::Event(event)));
            true
        } else {
            gst_log!(self.cat, obj: pad, "Forwarding event {:?}", event);
            self.src_pad.push_event(event)
        }
    }

    fn sink_query(&self, pad: &gst::Pad, _element: &Element, query: &mut gst::QueryRef) -> bool {
        gst_log!(self.cat, obj: pad, "Handling query {:?}", query);

        if query.is_serialized() {
            // FIXME: How can we do this?
            gst_log!(self.cat, obj: pad, "Dropping serialized query {:?}", query);
            false
        } else {
            gst_log!(self.cat, obj: pad, "Forwarding query {:?}", query);
            self.src_pad.peer_query(query)
        }
    }

    fn src_event(&self, pad: &gst::Pad, element: &Element, event: gst::Event) -> bool {
        use gst::EventView;

        gst_log!(self.cat, obj: pad, "Handling event {:?}", event);

        match event.view() {
            EventView::FlushStart(..) => {
                let _ = self.stop(element);
            }
            EventView::FlushStop(..) => {
                let (ret, state, pending) = element.get_state(0.into());
                if ret == gst::StateChangeReturn::Success && state == gst::State::Playing
                    || ret == gst::StateChangeReturn::Async && pending == gst::State::Playing
                {
                    let _ = self.start(element);
                }
            }
            _ => (),
        };

        gst_log!(self.cat, obj: pad, "Forwarding event {:?}", event);
        self.sink_pad.push_event(event)
    }

    fn src_query(&self, pad: &gst::Pad, _element: &Element, query: &mut gst::QueryRef) -> bool {
        use gst::QueryView;

        gst_log!(self.cat, obj: pad, "Handling query {:?}", query);
        match query.view_mut() {
            QueryView::Scheduling(ref mut q) => {
                let mut new_query = gst::Query::new_scheduling();
                let res = self.sink_pad.peer_query(&mut new_query);
                if !res {
                    return res;
                }

                gst_log!(self.cat, obj: pad, "Upstream returned {:?}", new_query);

                let (flags, min, max, align) = new_query.get_result();
                q.set(flags, min, max, align);
                q.add_scheduling_modes(&new_query
                    .get_scheduling_modes()
                    .iter()
                    .cloned()
                    .filter(|m| m != &gst::PadMode::Pull)
                    .collect::<Vec<_>>());
                gst_log!(self.cat, obj: pad, "Returning {:?}", q.get_mut_query());
                return true;
            }
            _ => (),
        };

        gst_log!(self.cat, obj: pad, "Forwarding query {:?}", query);
        self.sink_pad.peer_query(query)
    }

    fn push_item(&self, element: &Element, item: DataQueueItem) -> Result<(), gst::FlowError> {
        let res = match item {
            DataQueueItem::Buffer(buffer) => {
                gst_log!(self.cat, obj: element, "Forwarding buffer {:?}", buffer);
                self.src_pad.push(buffer).into_result().map(|_| ())
            }
            DataQueueItem::BufferList(list) => {
                gst_log!(self.cat, obj: element, "Forwarding buffer list {:?}", list);
                self.src_pad.push_list(list).into_result().map(|_| ())
            }
            DataQueueItem::Event(event) => {
                gst_log!(self.cat, obj: element, "Forwarding event {:?}", event);
                self.src_pad.push_event(event);
                Ok(())
            }
        };

        match res {
            Ok(_) => {
                gst_log!(self.cat, obj: element, "Successfully pushed item");
                let mut state = self.state.lock().unwrap();
                state.last_ret = gst::FlowReturn::Ok;
                Ok(())
            }
            Err(gst::FlowError::Flushing) => {
                gst_debug!(self.cat, obj: element, "Flushing");
                let mut state = self.state.lock().unwrap();
                if let Some(ref queue) = state.queue {
                    queue.pause();
                }
                state.last_ret = gst::FlowReturn::Flushing;
                Ok(())
            }
            Err(gst::FlowError::Eos) => {
                gst_debug!(self.cat, obj: element, "EOS");
                let mut state = self.state.lock().unwrap();
                if let Some(ref queue) = state.queue {
                    queue.pause();
                }
                state.last_ret = gst::FlowReturn::Eos;
                Ok(())
            }
            Err(err) => {
                gst_error!(self.cat, obj: element, "Got error {}", err);
                gst_element_error!(
                    element,
                    gst::StreamError::Failed,
                    ("Internal data stream error"),
                    ["streaming stopped, reason {}", err]
                );
                let mut state = self.state.lock().unwrap();
                state.last_ret = gst::FlowReturn::from_error(err);
                Err(gst::FlowError::CustomError)
            }
        }
    }

    fn prepare(&self, element: &Element) -> Result<(), gst::ErrorMessage> {
        gst_debug!(self.cat, obj: element, "Preparing");

        let settings = self.settings.lock().unwrap().clone();

        let mut state = self.state.lock().unwrap();

        let io_context = IOContext::new(
            &settings.context,
            settings.context_threads as isize,
            settings.context_wait,
        ).map_err(|err| {
            gst_error_msg!(
                gst::ResourceError::OpenRead,
                ["Failed to create IO context: {}", err]
            )
        })?;

        let dataqueue = DataQueue::new(&element.clone().upcast(), &settings);

        let element_clone = element.clone();
        let element_clone2 = element.clone();
        dataqueue
            .schedule(
                &io_context,
                move |item| {
                    let queue = element_clone.get_impl().downcast_ref::<Queue>().unwrap();
                    queue.push_item(&element_clone, item)
                },
                move |err| {
                    let queue = element_clone2.get_impl().downcast_ref::<Queue>().unwrap();
                    gst_error!(queue.cat, obj: &element_clone2, "Got error {}", err);
                    match err {
                        gst::FlowError::CustomError => (),
                        err => {
                            gst_element_error!(
                                element_clone2,
                                gst::StreamError::Failed,
                                ("Internal data stream error"),
                                ["streaming stopped, reason {}", err]
                            );
                        }
                    }
                },
            )
            .map_err(|_| {
                gst_error_msg!(
                    gst::ResourceError::OpenRead,
                    ["Failed to schedule data queue"]
                )
            })?;;

        state.io_context = Some(io_context);
        state.queue = Some(dataqueue);

        gst_debug!(self.cat, obj: element, "Prepared");

        Ok(())
    }

    fn unprepare(&self, element: &Element) -> Result<(), ()> {
        gst_debug!(self.cat, obj: element, "Unpreparing");

        let mut state = self.state.lock().unwrap();

        if let Some(ref queue) = state.queue {
            queue.shutdown();
        }

        *state = State::default();

        gst_debug!(self.cat, obj: element, "Unprepared");
        Ok(())
    }

    fn start(&self, element: &Element) -> Result<(), ()> {
        gst_debug!(self.cat, obj: element, "Starting");
        let mut state = self.state.lock().unwrap();

        if let Some(ref queue) = state.queue {
            queue.unpause();
        }
        state.last_ret = gst::FlowReturn::Ok;

        gst_debug!(self.cat, obj: element, "Started");

        Ok(())
    }

    fn stop(&self, element: &Element) -> Result<(), ()> {
        gst_debug!(self.cat, obj: element, "Stopping");
        let mut state = self.state.lock().unwrap();

        if let Some(ref queue) = state.queue {
            queue.pause();
            queue.clear(&self.src_pad);
        }
        state.last_ret = gst::FlowReturn::Flushing;

        gst_debug!(self.cat, obj: element, "Stopped");

        Ok(())
    }
}

impl ObjectImpl<Element> for Queue {
    fn set_property(&self, _obj: &glib::Object, id: u32, value: &glib::Value) {
        let prop = &PROPERTIES[id as usize];

        match *prop {
            Property::UInt("max-size-buffers", ..) => {
                let mut settings = self.settings.lock().unwrap();
                settings.max_size_buffers = value.get().unwrap();
            }
            Property::UInt("max-size-bytes", ..) => {
                let mut settings = self.settings.lock().unwrap();
                settings.max_size_bytes = value.get().unwrap();
            }
            Property::UInt64("max-size-time", ..) => {
                let mut settings = self.settings.lock().unwrap();
                settings.max_size_time = value.get().unwrap();
            }
            Property::String("context", ..) => {
                let mut settings = self.settings.lock().unwrap();
                settings.context = value.get().unwrap_or_else(|| "".into());
            }
            Property::Int("context-threads", ..) => {
                let mut settings = self.settings.lock().unwrap();
                settings.context_threads = value.get().unwrap();
            }
            Property::UInt("context-wait", ..) => {
                let mut settings = self.settings.lock().unwrap();
                settings.context_wait = value.get().unwrap();
            }
            _ => unimplemented!(),
        }
    }

    fn get_property(&self, _obj: &glib::Object, id: u32) -> Result<glib::Value, ()> {
        let prop = &PROPERTIES[id as usize];

        match *prop {
            Property::UInt("max-size-buffers", ..) => {
                let mut settings = self.settings.lock().unwrap();
                Ok(settings.max_size_buffers.to_value())
            }
            Property::UInt("max-size-bytes", ..) => {
                let mut settings = self.settings.lock().unwrap();
                Ok(settings.max_size_bytes.to_value())
            }
            Property::UInt64("max-size-time", ..) => {
                let mut settings = self.settings.lock().unwrap();
                Ok(settings.max_size_time.to_value())
            }
            Property::String("context", ..) => {
                let mut settings = self.settings.lock().unwrap();
                Ok(settings.context.to_value())
            }
            Property::Int("context-threads", ..) => {
                let mut settings = self.settings.lock().unwrap();
                Ok(settings.context_threads.to_value())
            }
            Property::UInt("context-wait", ..) => {
                let mut settings = self.settings.lock().unwrap();
                Ok(settings.context_wait.to_value())
            }
            _ => unimplemented!(),
        }
    }
}

impl ElementImpl<Element> for Queue {
    fn change_state(
        &self,
        element: &Element,
        transition: gst::StateChange,
    ) -> gst::StateChangeReturn {
        gst_trace!(self.cat, obj: element, "Changing state {:?}", transition);

        match transition {
            gst::StateChange::NullToReady => match self.prepare(element) {
                Err(err) => {
                    element.post_error_message(&err);
                    return gst::StateChangeReturn::Failure;
                }
                Ok(_) => (),
            },
            gst::StateChange::PausedToReady => match self.stop(element) {
                Err(_) => return gst::StateChangeReturn::Failure,
                Ok(_) => (),
            },
            gst::StateChange::ReadyToNull => match self.unprepare(element) {
                Err(_) => return gst::StateChangeReturn::Failure,
                Ok(_) => (),
            },
            _ => (),
        }

        let ret = element.parent_change_state(transition);
        if ret == gst::StateChangeReturn::Failure {
            return ret;
        }

        match transition {
            gst::StateChange::ReadyToPaused => match self.start(element) {
                Err(_) => return gst::StateChangeReturn::Failure,
                Ok(_) => (),
            },
            _ => (),
        }

        ret
    }
}

struct QueueStatic;

impl ImplTypeStatic<Element> for QueueStatic {
    fn get_name(&self) -> &str {
        "Queue"
    }

    fn new(&self, element: &Element) -> Box<ElementImpl<Element>> {
        Queue::init(element)
    }

    fn class_init(&self, klass: &mut ElementClass) {
        Queue::class_init(klass);
    }
}

pub fn register(plugin: &gst::Plugin) {
    let queue_static = QueueStatic;
    let type_ = register_type(queue_static);
    gst::Element::register(plugin, "ts-queue", 0, type_);
}