feat(multiplexer): Allow fine-grained control of concurrency strategy (#106)

pallas-multiplexer/src/agents.rs

@@ -0,0 +1,103 @@
+//! Interface to interact with the multiplexer as an agent
+
+use crate::Payload;
+
+use pallas_codec::{minicbor, Fragment};
+
+#[derive(Debug)]
+pub enum ChannelError {
+    NotConnected(Option<Payload>),
+    Encoding(String),
+    Decoding(String),
+}
+
+/// A raw link to the ingress / egress of the multiplexer
+pub trait Channel {
+    fn enqueue_chunk(&mut self, chunk: Payload) -> Result<(), ChannelError>;
+    fn dequeue_chunk(&mut self) -> Result<Payload, ChannelError>;
+}
+
+/// Protocol value that defines max segment length
+pub const MAX_SEGMENT_PAYLOAD_LENGTH: usize = 65535;
+
+enum Decoding<M> {
+    Done(M, usize),
+    NotEnoughData,
+    UnexpectedError(Box<dyn std::error::Error>),
+}
+
+fn try_decode_message<M>(buffer: &[u8]) -> Decoding<M>
+where
+    M: Fragment,
+{
+    let mut decoder = minicbor::Decoder::new(buffer);
+    let maybe_msg = decoder.decode();
+
+    match maybe_msg {
+        Ok(msg) => Decoding::Done(msg, decoder.position()),
+        Err(err) if err.is_end_of_input() => Decoding::NotEnoughData,
+        Err(err) => Decoding::UnexpectedError(Box::new(err)),
+    }
+}
+
+/// A channel abstraction to hide the complexity of partial payloads
+pub struct ChannelBuffer<'c, C: Channel> {
+    channel: &'c mut C,
+    temp: Vec<u8>,
+}
+
+impl<'c, C: Channel> ChannelBuffer<'c, C> {
+    pub fn new(channel: &'c mut C) -> Self {
+        Self {
+            channel,
+            temp: Vec::new(),
+        }
+    }
+
+    /// Enqueues a msg as a sequence payload chunks
+    pub fn send_msg_chunks<M>(&mut self, msg: &M) -> Result<(), ChannelError>
+    where
+        M: Fragment,
+    {
+        let mut payload = Vec::new();
+        minicbor::encode(&msg, &mut payload)
+            .map_err(|err| ChannelError::Encoding(err.to_string()))?;
+
+        let chunks = payload.chunks(MAX_SEGMENT_PAYLOAD_LENGTH);
+
+        for chunk in chunks {
+            self.channel.enqueue_chunk(Vec::from(chunk))?;
+        }
+
+        Ok(())
+    }
+
+    /// Reads from the channel until a complete message is found
+    pub fn recv_full_msg<M>(&mut self) -> Result<M, ChannelError>
+    where
+        M: Fragment,
+    {
+        // do an eager reading if buffer is empty, no point in going through the error
+        // handling
+        if self.temp.is_empty() {
+            let chunk = self.channel.dequeue_chunk()?;
+            self.temp.extend(chunk);
+        }
+
+        let decoding = try_decode_message::<M>(&self.temp);
+
+        match decoding {
+            Decoding::Done(msg, pos) => {
+                self.temp.drain(0..pos);
+                Ok(msg)
+            }
+            Decoding::UnexpectedError(err) => Err(ChannelError::Decoding(err.to_string())),
+            Decoding::NotEnoughData => {
+                let chunk = self.channel.dequeue_chunk()?;
+                self.temp.extend(chunk);
+
+                self.recv_full_msg()
+            }
+        }
+    }
+}

pallas-multiplexer/src/bearers.rs

@@ -5,35 +5,62 @@ use std::io::{Read, Write};
 use std::os::unix::net::UnixStream;
 use std::{net::TcpStream, time::Instant};
 
-use crate::{Bearer, Payload};
+use crate::Payload;
+
+pub struct Segment {
+    pub protocol: u16,
+    pub timestamp: u32,
+    pub payload: Payload,
+}
+
+pub trait Bearer: Read + Write + Send + Sync + Sized {
+    type Error: std::error::Error;
+
+    fn read_segment(&mut self) -> Result<Option<Segment>, Self::Error>;
+
+    fn write_segment(&mut self, segment: Segment) -> Result<(), Self::Error>;
+
+    fn clone(&self) -> Self;
+}
+
+impl Segment {
+    pub fn new(clock: Instant, protocol: u16, payload: Payload) -> Self {
+        Segment {
+            timestamp: clock.elapsed().as_micros() as u32,
+            protocol,
+            payload,
+        }
+    }
+}
+
+fn write_segment(writer: &mut impl Write, segment: Segment) -> Result<(), std::io::Error> {
+    let Segment {
+        timestamp,
+        protocol,
+        payload,
+    } = segment;
 
-fn write_segment(
-    writer: &mut impl Write,
-    clock: Instant,
-    protocol_id: u16,
-    payload: &[u8],
-) -> Result<(), std::io::Error> {
     let mut msg = Vec::new();
-    msg.write_u32::<NetworkEndian>(clock.elapsed().as_micros() as u32)?;
-    msg.write_u16::<NetworkEndian>(protocol_id)?;
+    msg.write_u32::<NetworkEndian>(timestamp)?;
+    msg.write_u16::<NetworkEndian>(protocol)?;
     msg.write_u16::<NetworkEndian>(payload.len() as u16)?;
 
     if log_enabled!(log::Level::Trace) {
         trace!(
             "sending segment, header {:?}, protocol id: {}, payload length: {}",
             hex::encode(&msg),
-            protocol_id,
+            protocol,
             payload.len()
         );
     }
 
-    msg.write_all(payload)?;
+    msg.write_all(&payload)?;
 
     writer.write_all(&msg)?;
     writer.flush()
 }
 
-fn read_segment(reader: &mut impl Read) -> Result<(u16, u32, Payload), std::io::Error> {
+fn read_segment(reader: &mut impl Read) -> Result<Segment, std::io::Error> {
     let mut header = [0u8; 8];
 
     reader.read_exact(&mut header)?;
@@ -43,12 +70,12 @@ fn read_segment(reader: &mut impl Read) -> Result<(u16, u32, Payload), std::io::
     }
 
     let length = NetworkEndian::read_u16(&header[6..]) as usize;
-    let id = NetworkEndian::read_u16(&header[4..6]) as usize ^ 0x8000;
-    let ts = NetworkEndian::read_u32(&header[0..4]);
+    let protocol = NetworkEndian::read_u16(&header[4..6]) as usize ^ 0x8000;
+    let timestamp = NetworkEndian::read_u32(&header[0..4]);
 
     debug!(
         "parsed inbound msg, protocol id: {}, ts: {}, payload length: {}",
-        id, ts, length
+        protocol, timestamp, length
     );
 
     let mut payload = vec![0u8; length];
@@ -58,44 +85,54 @@ fn read_segment(reader: &mut impl Read) -> Result<(u16, u32, Payload), std::io::
         trace!("read segment payload: {:?}", hex::encode(&payload));
     }
 
-    Ok((id as u16, ts, payload))
+    Ok(Segment {
+        protocol: protocol as u16,
+        timestamp,
+        payload,
+    })
+}
+
+fn read_segment_with_timeout(reader: &mut impl Read) -> Result<Option<Segment>, std::io::Error> {
+    match read_segment(reader) {
+        Ok(s) => Ok(Some(s)),
+        Err(err) => match err.kind() {
+            std::io::ErrorKind::WouldBlock => Ok(None),
+            std::io::ErrorKind::TimedOut => Ok(None),
+            std::io::ErrorKind::Interrupted => Ok(None),
+            _ => todo!(),
+        },
+    }
 }
 
 impl Bearer for TcpStream {
+    type Error = std::io::Error;
+
     fn clone(&self) -> Self {
         self.try_clone().expect("error cloning tcp stream")
     }
 
-    fn read_segment(&mut self) -> Result<(u16, u32, Payload), std::io::Error> {
-        read_segment(self)
+    fn read_segment(&mut self) -> Result<Option<Segment>, std::io::Error> {
+        read_segment_with_timeout(self)
     }
 
-    fn write_segment(
-        &mut self,
-        clock: Instant,
-        protocol_id: u16,
-        partial_payload: &[u8],
-    ) -> Result<(), std::io::Error> {
-        write_segment(self, clock, protocol_id, partial_payload)
+    fn write_segment(&mut self, segment: Segment) -> Result<(), std::io::Error> {
+        write_segment(self, segment)
     }
 }
 
 #[cfg(target_family = "unix")]
 impl Bearer for UnixStream {
+    type Error = std::io::Error;
+
     fn clone(&self) -> Self {
         self.try_clone().expect("error cloning unix stream")
     }
 
-    fn read_segment(&mut self) -> Result<(u16, u32, Payload), std::io::Error> {
-        read_segment(self)
+    fn read_segment(&mut self) -> Result<Option<Segment>, std::io::Error> {
+        read_segment_with_timeout(self)
     }
 
-    fn write_segment(
-        &mut self,
-        clock: Instant,
-        protocol_id: u16,
-        partial_payload: &[u8],
-    ) -> Result<(), std::io::Error> {
-        write_segment(self, clock, protocol_id, partial_payload)
+    fn write_segment(&mut self, segment: Segment) -> Result<(), std::io::Error> {
+        write_segment(self, segment)
     }
 }

pallas-multiplexer/src/demux.rs

@@ -0,0 +1,83 @@
+use std::collections::HashMap;
+
+use crate::{bearers::Bearer, std::Cancel, Payload};
+
+pub struct EgressError(pub Payload);
+
+pub trait Egress {
+    fn send(&self, payload: Payload) -> Result<(), EgressError>;
+}
+
+pub enum DemuxError<B: Bearer> {
+    BearerError(B::Error),
+    EgressDisconnected(u16, Payload),
+    EgressUnknown(u16, Payload),
+}
+
+pub enum TickOutcome {
+    Busy,
+    Idle,
+}
+
+/// A demuxer that reads from a bearer into the corresponding egress
+pub struct Demuxer<B, E> {
+    bearer: B,
+    egress: HashMap<u16, E>,
+}
+
+impl<B, E> Demuxer<B, E>
+where
+    B: Bearer,
+    E: Egress,
+{
+    pub fn new(bearer: B) -> Self {
+        Demuxer {
+            bearer,
+            egress: Default::default(),
+        }
+    }
+
+    pub fn register(&mut self, id: u16, tx: E) {
+        self.egress.insert(id, tx);
+    }
+
+    fn dispatch(&self, protocol: u16, payload: Payload) -> Result<(), DemuxError<B>> {
+        match self.egress.get(&protocol) {
+            Some(tx) => match tx.send(payload) {
+                Err(EgressError(p)) => Err(DemuxError::EgressDisconnected(protocol, p)),
+                Ok(_) => Ok(()),
+            },
+            None => Err(DemuxError::EgressUnknown(protocol, payload)),
+        }
+    }
+
+    pub fn tick(&mut self) -> Result<TickOutcome, DemuxError<B>> {
+        match self.bearer.read_segment() {
+            Err(err) => Err(DemuxError::BearerError(err)),
+            Ok(None) => Ok(TickOutcome::Idle),
+            Ok(Some(segment)) => match self.dispatch(segment.protocol, segment.payload) {
+                Err(err) => Err(err),
+                Ok(()) => Ok(TickOutcome::Busy),
+            },
+        }
+    }
+
+    pub fn block(&mut self, cancel: Cancel) -> Result<(), B::Error> {
+        loop {
+            match self.tick() {
+                Ok(TickOutcome::Busy) => (),
+                Ok(TickOutcome::Idle) => match cancel.is_set() {
+                    true => break Ok(()),
+                    false => (),
+                },
+                Err(DemuxError::BearerError(err)) => return Err(err),
+                Err(DemuxError::EgressDisconnected(id, _)) => {
+                    log::warn!("disconnected protocol {}", id)
+                }
+                Err(DemuxError::EgressUnknown(id, _)) => {
+                    log::warn!("unknown protocol {}", id)
+                }
+            }
+        }
+    }
+}

pallas-multiplexer/src/lib.rs

@@ -1,184 +1,41 @@
-mod bearers;
-
-use std::{
-    collections::HashMap,
-    io::{Read, Write},
-    sync::mpsc::{self, Receiver, Sender, TryRecvError},
-    thread::{self, JoinHandle},
-    time::{Duration, Instant},
-};
-
-use log::{debug, error, warn};
-
-pub trait Bearer: Read + Write + Send + Sync + Sized {
-    fn read_segment(&mut self) -> Result<(u16, u32, Payload), std::io::Error>;
-
-    fn write_segment(
-        &mut self,
-        clock: Instant,
-        protocol_id: u16,
-        partial_payload: &[u8],
-    ) -> Result<(), std::io::Error>;
-
-    fn clone(&self) -> Self;
-}
-
-const MAX_SEGMENT_PAYLOAD_LENGTH: usize = 65535;
+pub mod agents;
+pub mod bearers;
+pub mod demux;
+pub mod mux;
 
 pub type Payload = Vec<u8>;
 
-enum TxStepError {
-    BearerError(std::io::Error),
-    IngressDisconnected,
-    IngressEmpty,
+pub struct Multiplexer<B, I, E>
+where
+    B: bearers::Bearer,
+    I: mux::Ingress,
+    E: demux::Egress,
+{
+    pub muxer: mux::Muxer<B, I>,
+    pub demuxer: demux::Demuxer<B, E>,
 }
 
-fn tx_step<TBearer>(
-    bearer: &mut TBearer,
-    ingress_id: u16,
-    ingress_rx: &mut Receiver<Payload>,
-    clock: Instant,
-) -> Result<(), TxStepError>
+impl<B, I, E> Multiplexer<B, I, E>
 where
-    TBearer: Bearer,
+    B: bearers::Bearer,
+    I: mux::Ingress,
+    E: demux::Egress,
 {
-    match ingress_rx.try_recv() {
-        Ok(payload) => {
-            let chunks = payload.chunks(MAX_SEGMENT_PAYLOAD_LENGTH);
-
-            for chunk in chunks {
-                bearer
-                    .write_segment(clock, ingress_id, chunk)
-                    .map_err(TxStepError::BearerError)?;
-            }
-
-            Ok(())
-        }
-        Err(TryRecvError::Disconnected) => Err(TxStepError::IngressDisconnected),
-        Err(TryRecvError::Empty) => Err(TxStepError::IngressEmpty),
-    }
-}
-
-fn tx_loop<TBearer>(bearer: &mut TBearer, ingress: MuxIngress)
-where
-    TBearer: Bearer,
-{
-    let mut rx_map: HashMap<_, _> = ingress.into_iter().collect();
-
-    loop {
-        let clock = Instant::now();
-
-        rx_map.retain(|id, rx| match tx_step(bearer, *id, rx, clock) {
-            Err(TxStepError::BearerError(err)) => {
-                error!("{:?}", err);
-                panic!();
-            }
-            Err(TxStepError::IngressDisconnected) => {
-                warn!("protocol handle {} disconnected", id);
-                false
-            }
-            Err(TxStepError::IngressEmpty) => {
-                thread::sleep(Duration::from_millis(10));
-                true
-            }
-            Ok(_) => true,
-        });
-    }
-}
-
-fn rx_loop<TBearer>(bearer: &mut TBearer, egress: DemuxerEgress)
-where
-    TBearer: Bearer,
-{
-    let mut tx_map: HashMap<_, _> = egress.into_iter().collect();
-
-    loop {
-        match bearer.read_segment() {
-            Err(err) => {
-                error!("{:?}", err);
-                panic!();
-            }
-            Ok(segment) => {
-                let (id, _ts, payload) = segment;
-                match tx_map.get(&id) {
-                    Some(tx) => match tx.send(payload) {
-                        Err(err) => {
-                            error!("error sending egress tx to protocol, removing protocol from egress output. {:?}", err);
-                            tx_map.remove(&id);
-                        }
-                        Ok(_) => {
-                            debug!("successful tx to egress protocol");
-                        }
-                    },
-                    None => warn!("received segment for protocol id not being demuxed {}", id),
-                }
-            }
+    pub fn new(bearer: B) -> Self {
+        Multiplexer {
+            muxer: mux::Muxer::new(bearer.clone()),
+            demuxer: demux::Demuxer::new(bearer.clone()),
         }
     }
-}
 
-pub struct Channel(pub Sender<Payload>, pub Receiver<Payload>);
-
-type ChannelProtocolHandle = (u16, Channel);
-type ChannelIngressHandle = (u16, Receiver<Payload>);
-type ChannelEgressHandle = (u16, Sender<Payload>);
-type MuxIngress = Vec<ChannelIngressHandle>;
-type DemuxerEgress = Vec<ChannelEgressHandle>;
-
-pub struct Multiplexer {
-    tx_thread: JoinHandle<()>,
-    rx_thread: JoinHandle<()>,
-    io_handles: HashMap<u16, Channel>,
-}
-
-impl Multiplexer {
-    pub fn setup<TBearer>(
-        bearer: TBearer,
-        protocols: &[u16],
-    ) -> Result<Multiplexer, Box<dyn std::error::Error>>
-    where
-        TBearer: Bearer + 'static,
-    {
-        let handles = protocols.iter().map(|id| {
-            let (demux_tx, demux_rx) = mpsc::channel::<Payload>();
-            let (mux_tx, mux_rx) = mpsc::channel::<Payload>();
-
-            let channel = Channel(mux_tx, demux_rx);
-
-            let protocol_handle: ChannelProtocolHandle = (*id, channel);
-            let ingress_handle: ChannelIngressHandle = (*id, mux_rx);
-            let egress_handle: ChannelEgressHandle = (*id, demux_tx);
-
-            (protocol_handle, (ingress_handle, egress_handle))
-        });
-
-        let (protocol_handles, multiplex_handles): (Vec<_>, Vec<_>) = handles.into_iter().unzip();
-
-        let (ingress, egress): (Vec<_>, Vec<_>) = multiplex_handles.into_iter().unzip();
-
-        let mut tx_bearer = bearer.clone();
-        let tx_thread = thread::spawn(move || tx_loop(&mut tx_bearer, ingress));
-
-        let mut rx_bearer = bearer.clone();
-        let rx_thread = thread::spawn(move || rx_loop(&mut rx_bearer, egress));
-
-        let io_handles: HashMap<u16, Channel> = protocol_handles.into_iter().collect();
-
-        Ok(Multiplexer {
-            io_handles,
-            tx_thread,
-            rx_thread,
-        })
-    }
-
-    pub fn use_channel(&mut self, protocol_id: u16) -> Channel {
-        self.io_handles
-            .remove(&protocol_id)
-            .expect("requested channel not found in multiplexer")
-    }
-
-    pub fn join(self) {
-        self.tx_thread.join().expect("error joining tx loop thread");
-        self.rx_thread.join().expect("error joining rx loop thread");
+    pub fn register_channel(&mut self, protocol: u16, ingress: I, egress: E) {
+        self.muxer.register(protocol, ingress);
+        self.demuxer.register(protocol, egress);
     }
 }
+
+#[cfg(feature = "std")]
+mod std;
+
+#[cfg(feature = "std")]
+pub use crate::std::*;

pallas-multiplexer/src/mux.rs

@@ -0,0 +1,122 @@
+use std::{collections::HashMap, time::Instant};
+
+use rand::seq::SliceRandom;
+use rand::thread_rng;
+
+use crate::{
+    bearers::{Bearer, Segment},
+    std::Cancel,
+    Payload,
+};
+
+pub enum IngressError {
+    Disconnected,
+    Empty,
+}
+
+/// Source of payloads for a particular protocol
+///
+/// To be implemented by any mechanism that allows to submit a payloads from a
+/// particular protocol that need to be muxed by the multiplexer.
+pub trait Ingress {
+    fn try_recv(&mut self) -> Result<Payload, IngressError>;
+}
+
+type Message = (u16, Payload);
+
+pub enum TickOutcome<TBearer>
+where
+    TBearer: Bearer,
+{
+    BearerError(TBearer::Error),
+    Idle,
+    Busy,
+}
+
+pub struct Muxer<B, I> {
+    bearer: B,
+    ingress: HashMap<u16, I>,
+    clock: Instant,
+}
+
+impl<B, I> Muxer<B, I>
+where
+    B: Bearer,
+    I: Ingress,
+{
+    pub fn new(bearer: B) -> Self {
+        Self {
+            bearer,
+            ingress: Default::default(),
+            clock: Instant::now(),
+        }
+    }
+
+    /// Register the receiver end of an ingress channel
+    pub fn register(&mut self, id: u16, rx: I) {
+        self.ingress.insert(id, rx);
+    }
+
+    /// Remove a protocol from the ingress
+    ///
+    /// Meant to be used after a receive error in a previous tick
+    pub fn deregister(&mut self, id: u16) {
+        self.ingress.remove(&id);
+    }
+
+    #[inline]
+    fn randomize_ids(&self) -> Vec<u16> {
+        let mut rng = thread_rng();
+        let mut keys: Vec<_> = self.ingress.keys().cloned().collect();
+        keys.shuffle(&mut rng);
+        keys
+    }
+
+    /// Select the next segment to be muxed
+    ///
+    /// This method iterates over the existing receivers checking for the first
+    /// available message. The order of the checks is random to ensure a fair
+    /// use of the multiplexer amongst all protocols.
+    pub fn select(&mut self) -> Option<Message> {
+        for id in self.randomize_ids() {
+            let rx = self.ingress.get_mut(&id).unwrap();
+
+            match rx.try_recv() {
+                Ok(payload) => return Some((id, payload)),
+                Err(IngressError::Disconnected) => {
+                    self.deregister(id);
+                }
+                _ => (),
+            };
+        }
+
+        None
+    }
+
+    pub fn tick(&mut self) -> TickOutcome<B> {
+        match self.select() {
+            Some((id, payload)) => {
+                let segment = Segment::new(self.clock, id, payload);
+
+                match self.bearer.write_segment(segment) {
+                    Err(err) => TickOutcome::BearerError(err),
+                    _ => TickOutcome::Busy,
+                }
+            }
+            None => TickOutcome::Idle,
+        }
+    }
+
+    pub fn block(&mut self, cancel: Cancel) -> Result<(), B::Error> {
+        loop {
+            match self.tick() {
+                TickOutcome::BearerError(err) => return Err(err),
+                TickOutcome::Idle => match cancel.is_set() {
+                    true => break Ok(()),
+                    false => std::thread::yield_now(),
+                },
+                TickOutcome::Busy => (),
+            }
+        }
+    }
+}

pallas-multiplexer/src/std.rs

@@ -0,0 +1,123 @@
+use crate::{agents, bearers::Bearer, demux, mux, Payload};
+
+use std::{
+    sync::{
+        atomic::{AtomicBool, Ordering},
+        mpsc::{channel, Receiver, SendError, Sender, TryRecvError},
+        Arc,
+    },
+    thread::{spawn, JoinHandle},
+};
+
+pub type StdIngress = Receiver<Payload>;
+
+impl mux::Ingress for StdIngress {
+    fn try_recv(&mut self) -> Result<Payload, mux::IngressError> {
+        match Receiver::try_recv(self) {
+            Ok(x) => Ok(x),
+            Err(TryRecvError::Disconnected) => Err(mux::IngressError::Disconnected),
+            Err(TryRecvError::Empty) => Err(mux::IngressError::Empty),
+        }
+    }
+}
+
+pub type StdEgress = Sender<Payload>;
+
+impl demux::Egress for StdEgress {
+    fn send(&self, payload: Payload) -> Result<(), demux::EgressError> {
+        match Sender::send(self, payload) {
+            Ok(_) => Ok(()),
+            Err(SendError(p)) => Err(demux::EgressError(p)),
+        }
+    }
+}
+
+pub type StdPlexer<B> = crate::Multiplexer<B, StdIngress, StdEgress>;
+
+pub type StdChannel = (Sender<Payload>, Receiver<Payload>);
+
+impl agents::Channel for StdChannel {
+    fn enqueue_chunk(&mut self, payload: Payload) -> Result<(), agents::ChannelError> {
+        match self.0.send(payload) {
+            Ok(_) => Ok(()),
+            Err(SendError(payload)) => Err(agents::ChannelError::NotConnected(Some(payload))),
+        }
+    }
+
+    fn dequeue_chunk(&mut self) -> Result<Payload, agents::ChannelError> {
+        match self.1.recv() {
+            Ok(payload) => Ok(payload),
+            Err(_) => Err(agents::ChannelError::NotConnected(None)),
+        }
+    }
+}
+
+pub fn use_channel<B: Bearer>(plexer: &mut StdPlexer<B>, protocol: u16) -> StdChannel {
+    let (demux_tx, demux_rx) = channel::<Payload>();
+    let (mux_tx, mux_rx) = channel::<Payload>();
+
+    plexer.register_channel(protocol, mux_rx, demux_tx);
+
+    (mux_tx, demux_rx)
+}
+
+#[derive(Clone, Debug, Default)]
+pub struct Cancel(Arc<AtomicBool>);
+
+impl Cancel {
+    pub fn set(&self) {
+        self.0.store(true, Ordering::SeqCst);
+    }
+
+    pub fn is_set(&self) -> bool {
+        self.0.load(Ordering::SeqCst)
+    }
+}
+
+#[derive(Debug)]
+pub struct Loop<B>
+where
+    B: Bearer,
+{
+    cancel: Cancel,
+    thread: JoinHandle<Result<(), B::Error>>,
+}
+
+impl<B> Loop<B>
+where
+    B: Bearer,
+{
+    pub fn cancel(&self) {
+        self.cancel.set();
+    }
+
+    pub fn join(self) -> Result<(), B::Error> {
+        self.thread.join().unwrap()
+    }
+}
+
+pub fn spawn_muxer<B, I>(mut muxer: mux::Muxer<B, I>) -> Loop<B>
+where
+    B: Bearer + 'static,
+    B::Error: Send,
+    I: mux::Ingress + Send + 'static,
+{
+    let cancel = Cancel::default();
+    let cancel2 = cancel.clone();
+    let thread = spawn(move || muxer.block(cancel2));
+
+    Loop { cancel, thread }
+}
+
+pub fn spawn_demuxer<B, E>(mut demuxer: demux::Demuxer<B, E>) -> Loop<B>
+where
+    B: Bearer + 'static,
+    B::Error: Send,
+    E: demux::Egress + Send + 'static,
+{
+    let cancel = Cancel::default();
+    let cancel2 = cancel.clone();
+    let thread = spawn(move || demuxer.block(cancel2));
+
+    Loop { cancel, thread }
+}