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//! Bus provides a lock-free, bounded, single-producer, multi-consumer, broadcast channel. //! //! It uses a circular buffer and atomic instructions to implement a lock-free single-producer, //! multi-consumer channel. The interface is similar to that of the `std::sync::mpsc` channels, //! except that multiple consumers (readers of the channel) can be produced, whereas only a single //! sender can exist. Furthermore, in contrast to most multi-consumer FIFO queues, bus is //! *broadcast*; every send goes to every consumer. //! //! I haven't seen this particular implementation in literature (some extra bookkeeping is //! necessary to allow multiple consumers), but a lot of related reading can be found in Ross //! Bencina's blog post ["Some notes on lock-free and wait-free //! algorithms"](http://www.rossbencina.com/code/lockfree). //! //! Bus achieves broadcast by cloning the element in question, which is why `T` must implement //! `Clone`. However, Bus is clever about only cloning when necessary. Specifically, the last //! consumer to see a given value will move it instead of cloning, which means no cloning is //! happening for the single-consumer case. For cases where cloning is expensive, `Arc` should be //! used instead. //! //! In a single-producer, single-consumer setup (which is the only one that Bus and //! `mpsc::sync_channel` both support), Bus gets ~2x the performance of `mpsc::sync_channel` on //! my machine. YMMV. You can check your performance on Nightly using //! //! ```console //! $ cargo bench --features bench //! ``` //! //! To see multi-consumer results, run the benchmark utility instead (should work on stable too) //! //! ```console //! $ cargo build --bin bench --release //! $ target/release/bench //! ``` //! //! # Examples //! //! Single-send, multi-consumer example //! //! ```rust //! use bus::Bus; //! let mut bus = Bus::new(10); //! let mut rx1 = bus.add_rx(); //! let mut rx2 = bus.add_rx(); //! //! bus.broadcast("Hello"); //! assert_eq!(rx1.recv(), Ok("Hello")); //! assert_eq!(rx2.recv(), Ok("Hello")); //! ``` //! //! Multi-send, multi-consumer example //! //! ```rust //! use bus::Bus; //! use std::thread; //! //! let mut bus = Bus::new(10); //! let mut rx1 = bus.add_rx(); //! let mut rx2 = bus.add_rx(); //! //! // start a thread that sends 1..100 //! let j = thread::spawn(move || { //! for i in 1..100 { //! bus.broadcast(i); //! } //! }); //! //! // every value should be received by both receivers //! for i in 1..100 { //! // rx1 //! assert_eq!(rx1.recv(), Ok(i)); //! // and rx2 //! assert_eq!(rx2.recv(), Ok(i)); //! } //! //! j.join().unwrap(); //! ``` //! //! Many-to-many channel using a dispatcher //! //! ```rust //! use bus::Bus; //! //! use std::thread; //! use std::sync::mpsc; //! //! // set up fan-in //! let (tx1, mix_rx) = mpsc::sync_channel(100); //! let tx2 = tx1.clone(); //! // set up fan-out //! let mut mix_tx = Bus::new(100); //! let mut rx1 = mix_tx.add_rx(); //! let mut rx2 = mix_tx.add_rx(); //! // start dispatcher //! thread::spawn(move || { //! for m in mix_rx.iter() { //! mix_tx.broadcast(m); //! } //! }); //! //! // sends on tx1 are received ... //! tx1.send("Hello").unwrap(); //! //! // ... by both receiver rx1 ... //! assert_eq!(rx1.recv(), Ok("Hello")); //! // ... and receiver rx2 //! assert_eq!(rx2.recv(), Ok("Hello")); //! //! // same with sends on tx2 //! tx2.send("world").unwrap(); //! assert_eq!(rx1.recv(), Ok("world")); //! assert_eq!(rx2.recv(), Ok("world")); //! ``` #![deny(missing_docs)] #![cfg_attr(feature = "bench", feature(test))] extern crate atomic_option; use atomic_option::AtomicOption; extern crate parking_lot_core; use parking_lot_core::SpinWait; #[cfg(feature = "bench")] extern crate test; #[cfg(feature = "async")] extern crate futures; #[cfg(feature = "async")] extern crate void; use std::sync::atomic; use std::sync::mpsc; use std::thread; use std::time; use std::cell::UnsafeCell; use std::ops::Deref; use std::sync::Arc; const SPINTIME: u32 = 100000; //ns struct SeatState<T> { max: usize, val: Option<T>, } struct MutSeatState<T>(UnsafeCell<SeatState<T>>); unsafe impl<T> Sync for MutSeatState<T> {} impl<T> Deref for MutSeatState<T> { type Target = UnsafeCell<SeatState<T>>; fn deref(&self) -> &Self::Target { &self.0 } } /// A Seat is a single location in the circular buffer. /// Each Seat knows how many readers are expected to access it, as well as how many have. The /// producer will never modify a seat's state unless all readers for a particular seat have either /// called `.take()` on it, or have left (see `Bus.rleft`). /// /// The producer walks the seats of the ring in order, and will always only modify the seat at /// `tail + 1` once all readers have finished with the seat at `head + 2`. A reader will never /// access a seat unless it is between the reader's `head` and the producer's `tail`. Together, /// these properties ensure that a Seat is either accessed only by readers, or by only the /// producer. /// /// The `read` attribute is used to ensure that readers see the most recent write to the seat when /// they access it. This is done using `atomic::Ordering::Acquire` and `atomic::Ordering::Release`. struct Seat<T> { read: atomic::AtomicUsize, state: MutSeatState<T>, // is the writer waiting for this seat to be emptied? needs to be atomic since both the last // reader and the writer might be accessing it at the same time. waiting: AtomicOption<thread::Thread>, } impl<T: Clone + Sync> Seat<T> { /// take is used by a reader to extract a copy of the value stored on this seat. only readers /// that were created strictly before the time this seat was last written to by the producer /// are allowed to call this method, and they may each only call it once. fn take(&self) -> T { let read = self.read.load(atomic::Ordering::Acquire); // the writer will only modify this element when .read hits .max - writer.rleft[i]. we can // be sure that this is not currently the case (which means it's safe for us to read) // because: // // - .max is set to the number of readers at the time when the write happens // - any joining readers will start at a later seat // - so, at most .max readers will call .take() on this seat this time around the buffer // - a reader must leave either *before* or *after* a call to recv. there are two cases: // // - it leaves before, rleft is decremented, but .take is not called // - it leaves after, .take is called, but head has been incremented, so rleft will be // decremented for the *next* seat, not this one // // so, either .take is called, and .read is incremented, or writer.rleft is incremented. // thus, for a writer to modify this element, *all* readers at the time of the previous // write to this seat must have either called .take or have left. // - since we are one of those readers, this cannot be true, so it's safe for us to assume // that there is no concurrent writer for this seat let state = unsafe { &*self.state.get() }; assert!(read < state.max, "reader hit seat with exhausted reader count"); let mut waiting = None; // NOTE // we must extract the value *before* we decrement the number of remaining items otherwise, // the object might be replaced by the time we read it! let v = if read + 1 == state.max { // we're the last reader, so we may need to notify the writer there's space in the buf. // can be relaxed, since the acquire at the top already guarantees that we'll see // updates. waiting = self.waiting.take(atomic::Ordering::Relaxed); // since we're the last reader, no-one else will be cloning this value, so we can // safely take a mutable reference, and just take the val instead of cloning it. unsafe { &mut *self.state.get() }.val.take().unwrap() } else { state.val.clone().expect("seat that should be occupied was empty") }; // let writer know that we no longer need this item. // state is no longer safe to access. drop(state); self.read.fetch_add(1, atomic::Ordering::AcqRel); if let Some(t) = waiting { // writer was waiting for us to finish with this t.unpark(); } return v; } } impl<T> Default for Seat<T> { fn default() -> Self { Seat { read: atomic::AtomicUsize::new(0), waiting: AtomicOption::empty(), state: MutSeatState(UnsafeCell::new(SeatState { max: 0, val: None, })), } } } /// BusInner encapsulates data that both the writer and the readers need to access. /// The tail is only ever modified by the producer, and read by the consumers. /// The length of the bus is instantiated when the bus is created, and is never modified. struct BusInner<T> { ring: Vec<Seat<T>>, len: usize, tail: atomic::AtomicUsize, closed: atomic::AtomicBool, } /// Bus is the main interconnect for broadcast messages. /// It can be used to send broadcast messages, or to connect additional consumers. /// When the Bus is dropped, receivers will continue receiving any outstanding broadcast messages /// they would have received if the bus were not dropped. After all those messages have been /// received, any subsequent receive call on a receiver will return a disconnected error. pub struct Bus<T> { state: Arc<BusInner<T>>, // current number of readers readers: usize, // rleft keeps track of readers that should be skipped for each index. we must do this because // .read will be < max for those indices, even though all active readers have received them. rleft: Vec<usize>, // leaving is used by receivers to signal that they are done leaving: (mpsc::Sender<usize>, mpsc::Receiver<usize>), // waiting is used by receivers to signal that they are waiting for new entries, and where they // are waiting waiting: (mpsc::Sender<(thread::Thread, usize)>, mpsc::Receiver<(thread::Thread, usize)>), // channel used to communicate to unparker that a given thread should be woken up unpark: mpsc::Sender<thread::Thread>, // cache used to keep track of threads waiting for next write. // this is only here to avoid allocating one on every broadcast() cache: Vec<(thread::Thread, usize)>, } impl<T> Bus<T> { /// Allocates a new bus. /// /// The provided length should be sufficient to absorb temporary peaks in the data flow, and is /// thus workflow-dependent. Bus performance degrades somewhat when the queue is full, so it is /// generally better to set this high than low unless you are pressed for memory. pub fn new(mut len: usize) -> Bus<T> { use std::iter; // ring buffer must have room for one padding element len += 1; let inner = Arc::new(BusInner { ring: (0..len).map(|_| Seat::default()).collect(), tail: atomic::AtomicUsize::new(0), closed: atomic::AtomicBool::new(false), len: len, }); // we run a separate thread responsible for unparking // so we don't have to wait for unpark() to return in broadcast_inner // sending on a channel without contention is cheap, unparking is not let (unpark_tx, unpark_rx) = mpsc::channel::<thread::Thread>(); thread::spawn(move || for t in unpark_rx.iter() { t.unpark(); }); Bus { state: inner, readers: 0, rleft: iter::repeat(0).take(len).collect(), leaving: mpsc::channel(), waiting: mpsc::channel(), unpark: unpark_tx, cache: Vec::new(), } } /// Get the expected number of reads for the given seat. /// This number will always be conservative, in that fewer reads may be fine. Specifically, /// `.rleft` may not be sufficiently up-to-date to account for all readers that have left. #[inline] fn expected(&mut self, at: usize) -> usize { // since only the producer will modify the ring, and &mut self guarantees that *we* are the // producer, no-one is modifying the ring. Multiple read-only borrows are safe, and so the // cast below is safe. unsafe { &*self.state.ring[at].state.get() }.max - self.rleft[at] } /// Attempts to place the given value on the bus. /// /// If the bus is full, the behavior depends on `block`. If false, the value given is returned /// in an `Err()`. Otherwise, the current thread will be parked until there is space in the bus /// again, and the broadcast will be tried again until it succeeds. /// /// Note that broadcasts will succeed even if there are no consumers! fn broadcast_inner(&mut self, val: T, block: bool) -> Result<(), T> { let tail = self.state.tail.load(atomic::Ordering::Relaxed); // we want to check if the next element over is free to ensure that we always leave one // empty space between the head and the tail. This is necessary so that readers can // distinguish between an empty and a full list. If the fence seat is free, the seat at // tail must also be free, which is simple enough to show by induction (exercise for the // reader). let fence = (tail + 1) % self.state.len; let spintime = time::Duration::new(0, SPINTIME); // to avoid parking when a slot frees up quickly, we use an exponential back-off SpinWait. let mut sw = SpinWait::new(); loop { let fence_read = self.state.ring[fence].read.load(atomic::Ordering::Acquire); // is there room left in the ring? if fence_read == self.expected(fence) { break; } // no! // let's check if any readers have left, which might increment self.rleft[tail]. while let Ok(mut left) = self.leaving.1.try_recv() { // a reader has left! this means that every seat between `left` and `tail-1` // has max set one too high. we track the number of such "missing" reads that // should be ignored in self.rleft, and compensate for them when looking at // seat.read above. self.readers -= 1; while left != tail { self.rleft[left] += 1; left = (left + 1) % self.state.len } } // is the fence block now free? if fence_read == self.expected(fence) { // yes! go ahead and write! break; } else if block { // no, so block by parking and telling readers to notify on last read self.state.ring[fence] .waiting .replace(Some(Box::new(thread::current())), atomic::Ordering::Relaxed); // need the atomic fetch_add to ensure reader threads will see the new .waiting self.state.ring[fence].read.fetch_add(0, atomic::Ordering::Release); if !sw.spin() { // not likely to get a slot soon -- wait to be unparked instead. // note that we *need* to wait, because there are some cases in which we // *won't* be unparked even though a slot has opened up. thread::park_timeout(spintime); } continue; } else { // no, and blocking isn't allowed, so return an error return Err(val); } } // next one over is free, we have a free seat! let readers = self.readers; { let next = &self.state.ring[tail]; // we are the only writer, so no-one else can be writing. however, since we're // mutating state, we also need for there to be no readers for this to be safe. the // argument for why this is the case is roughly an inverse of the argument for why // the unsafe block in Seat.take() is safe. basically, since // // .read + .rleft == .max // // we know all readers at the time of the seat's previous write have accessed this // seat. we also know that no other readers will access that seat (they must have // started at later seats). thus, we are the only thread accessing this seat, and // so we can safely access it as mutable. let state = unsafe { &mut *next.state.get() }; state.max = readers; state.val = Some(val); next.waiting.replace(None, atomic::Ordering::Relaxed); next.read.store(0, atomic::Ordering::Release); } self.rleft[tail] = 0; // now tell readers that they can read let tail = (tail + 1) % self.state.len; self.state.tail.store(tail, atomic::Ordering::Release); // unblock any blocked receivers while let Ok((t, at)) = self.waiting.1.try_recv() { // the only readers we can't unblock are those that have already absorbed the // broadcast we just made, since they are blocking on the *next* broadcast if at == tail { self.cache.push((t, at)) } else { self.unpark.send(t).unwrap(); } } for w in self.cache.drain(..) { // fine to do here because it is guaranteed not to block self.waiting.0.send(w).unwrap(); } Ok(()) } /// Attempt to broadcast the given value to all consumers, but do not wait if bus is full. /// /// /// Attempts to broadcast a value on this bus, returning it back if it could not be sent. /// /// Note that, in contrast to regular channels, a bus is *not* considered closed if there are /// no consumers, and thus broadcasts will continue to succeed. Thus, a successful broadcast /// occurs as long as there is room on the internal bus to store the value, or some older value /// has been received by all consumers. Note that a return value of `Err` means that the data /// will never be received (by any consumer), but a return value of Ok does not mean that the /// data will be received by a given consumer. It is possible for a receiver to hang up /// immediately after this function returns Ok. /// /// This method will never block the current thread. /// /// ```rust /// use bus::Bus; /// let mut tx = Bus::new(1); /// let mut rx = tx.add_rx(); /// assert_eq!(tx.try_broadcast("Hello"), Ok(())); /// assert_eq!(tx.try_broadcast("world"), Err("world")); /// ``` pub fn try_broadcast(&mut self, val: T) -> Result<(), T> { self.broadcast_inner(val, false) } /// Broadcasts a value on the bus to all consumers. /// /// This function will block until space in the internal buffer becomes available. /// /// Note that a successful send does not guarantee that the receiver will ever see the data if /// there is a buffer on this channel. Items may be enqueued in the internal buffer for the /// receiver to receive at a later time. Furthermore, in contrast to regular channels, a bus is /// *not* considered closed if there are no consumers, and thus broadcasts will continue to /// succeed. pub fn broadcast(&mut self, val: T) { if let Err(..) = self.broadcast_inner(val, true) { unreachable!("blocking broadcast_inner can't fail"); } } /// Add a new consumer to this bus. /// /// The new consumer will receive all *future* broadcasts on this bus. /// /// # Examples /// /// ```rust /// use bus::Bus; /// use std::sync::mpsc::TryRecvError; /// /// let mut bus = Bus::new(10); /// let mut rx1 = bus.add_rx(); /// /// bus.broadcast("Hello"); /// /// // consumer present during broadcast sees update /// assert_eq!(rx1.recv(), Ok("Hello")); /// /// // new consumer does *not* see broadcast /// let mut rx2 = bus.add_rx(); /// assert_eq!(rx2.try_recv(), Err(TryRecvError::Empty)); /// /// // both consumers see new broadcast /// bus.broadcast("world"); /// assert_eq!(rx1.recv(), Ok("world")); /// assert_eq!(rx2.recv(), Ok("world")); /// ``` pub fn add_rx(&mut self) -> BusReader<T> { self.readers += 1; BusReader { bus: self.state.clone(), head: self.state.tail.load(atomic::Ordering::Relaxed), leaving: self.leaving.0.clone(), waiting: self.waiting.0.clone(), closed: false, } } } impl<T> Drop for Bus<T> { fn drop(&mut self) { self.state.closed.store(true, atomic::Ordering::Relaxed); // Acquire/Release .tail to ensure other threads see new .closed self.state.tail.fetch_add(0, atomic::Ordering::AcqRel); // TODO: unpark receivers -- this is not absolutely necessary, since the reader's park will // time out, but it would cause them to detect the closed bus somewhat faster. } } enum RecvCondition { Try, Block, Timeout(time::Duration), } /// A BusReader is a single consumer of Bus broadcasts. /// It will see every new value that is passed to `.broadcast()` (or successful calls to /// `.try_broadcast()`) on the Bus that it was created from. /// /// Dropping a BusReader is perfectly safe, and will unblock the writer if it was waiting for that /// read to see a particular update. /// /// ```rust /// use bus::Bus; /// let mut tx = Bus::new(1); /// let mut r1 = tx.add_rx(); /// let r2 = tx.add_rx(); /// assert_eq!(tx.try_broadcast(true), Ok(())); /// assert_eq!(r1.recv(), Ok(true)); /// /// // the bus does not have room for another broadcast /// // since it knows r2 has not yet read the first broadcast /// assert_eq!(tx.try_broadcast(true), Err(true)); /// /// // dropping r2 tells the producer that there is a free slot /// // (i.e., it has been read by everyone) /// drop(r2); /// assert_eq!(tx.try_broadcast(true), Ok(())); /// ``` pub struct BusReader<T> { bus: Arc<BusInner<T>>, head: usize, leaving: mpsc::Sender<usize>, waiting: mpsc::Sender<(thread::Thread, usize)>, closed: bool, } impl<T: Clone + Sync> BusReader<T> { /// Attempts to read a broadcast from the bus. /// /// If the bus is empty, the behavior depends on `block`. If false, /// `Err(mpsc::RecvTimeoutError::Timeout)` is returned. Otherwise, the current thread will be /// parked until there is another broadcast on the bus, at which point the receive will be /// performed. fn recv_inner(&mut self, block: RecvCondition) -> Result<T, mpsc::RecvTimeoutError> { if self.closed { return Err(mpsc::RecvTimeoutError::Disconnected); } let start = match block { RecvCondition::Timeout(_) => Some(time::Instant::now()), _ => None, }; let spintime = time::Duration::new(0, SPINTIME); let mut was_closed = false; let mut sw = SpinWait::new(); let mut first = true; loop { let tail = self.bus.tail.load(atomic::Ordering::Acquire); if tail != self.head { break; } // buffer is empty, check whether it's closed. // relaxed is fine since Bus.drop does an acquire/release on tail if self.bus.closed.load(atomic::Ordering::Relaxed) { // we need to check again that there's nothing in the bus, otherwise we might have // missed a write between when we did the read of .tail above and when we read // .closed here if !was_closed { was_closed = true; continue; } // the bus is closed, and we didn't miss anything! self.closed = true; return Err(mpsc::RecvTimeoutError::Disconnected); } // not closed, should we block? if let RecvCondition::Try = block { return Err(mpsc::RecvTimeoutError::Timeout); } // park and tell writer to notify on write if first { if let Err(..) = self.waiting.send((thread::current(), self.head)) { // writer has gone away, but this is not a reliable way to check // in particular, we may also have missed updates unimplemented!(); } first = false; } if !sw.spin() { match block { RecvCondition::Timeout(ref t) => { match t.checked_sub(start.as_ref().unwrap().elapsed()) { Some(left) => { if left < spintime { thread::park_timeout(left); } else { thread::park_timeout(spintime); } } None => { // So, the wake-up thread is still going to try to wake us up later // since we sent thread::current() above, but that's fine. return Err(mpsc::RecvTimeoutError::Timeout); } } } RecvCondition::Block => { thread::park_timeout(spintime); } RecvCondition::Try => unreachable!(), } } } let head = self.head; let ret = self.bus.ring[head].take(); // safe because len is read-only self.head = (head + 1) % self.bus.len; Ok(ret) } /// Attempts to return a pending broadcast on this receiver without blocking. /// /// This method will never block the caller in order to wait for data to become available. /// Instead, this will always return immediately with a possible option of pending data on the /// channel. /// /// If the corresponding bus has been dropped, and all broadcasts have been received, this /// method will return with a disconnected error. /// /// This mehtod is useful for a flavor of "optimistic check" before deciding to block on a /// receiver. /// /// ```rust /// use bus::Bus; /// use std::thread; /// /// let mut tx = Bus::new(10); /// let mut rx = tx.add_rx(); /// /// // spawn a thread that will broadcast at some point /// let j = thread::spawn(move || { /// tx.broadcast(true); /// }); /// /// loop { /// match rx.try_recv() { /// Ok(val) => { /// assert_eq!(val, true); /// break; /// } /// Err(..) => { /// // maybe we can do other useful work here /// // or we can just busy-loop /// thread::yield_now() /// }, /// } /// } /// /// j.join().unwrap(); /// ``` pub fn try_recv(&mut self) -> Result<T, mpsc::TryRecvError> { self.recv_inner(RecvCondition::Try).map_err(|e| match e { mpsc::RecvTimeoutError::Disconnected => mpsc::TryRecvError::Disconnected, mpsc::RecvTimeoutError::Timeout => mpsc::TryRecvError::Empty, }) } /// Read another broadcast message from the bus, and block if none are available. /// /// This function will always block the current thread if there is no data available and it's /// possible for more broadcasts to be sent. Once a broadcast is sent on the corresponding Bus, /// then this receiver will wake up and return that message. /// /// If the corresponding `Bus` has been dropped, or it is dropped while this call is blocking, /// this call will wake up and return Err to indicate that no more messages can ever be /// received on this channel. However, since channels are buffered, messages sent before the /// disconnect will still be properly received. pub fn recv(&mut self) -> Result<T, mpsc::RecvError> { match self.recv_inner(RecvCondition::Block) { Ok(val) => Ok(val), Err(mpsc::RecvTimeoutError::Disconnected) => Err(mpsc::RecvError), _ => unreachable!("blocking recv_inner can't fail"), } } /// Attempts to wait for a value from the bus, returning an error if the corresponding channel /// has hung up, or if it waits more than `timeout`. /// /// This function will always block the current thread if there is no data available and it's /// possible for more broadcasts to be sent. Once a message is sent on the corresponding `Bus`, /// then this receiver will wake up and return that message. /// /// If the corresponding `Bus` has been dropped, or it is dropped while this call is blocking, /// this call will wake up and return Err to indicate that no more messages can ever be /// received on this channel. However, since channels are buffered, messages sent before the /// disconnect will still be properly received. /// /// # Examples /// /// ```rust /// use bus::Bus; /// use std::sync::mpsc::RecvTimeoutError; /// use std::time::Duration; /// /// let mut tx = Bus::<bool>::new(10); /// let mut rx = tx.add_rx(); /// /// let timeout = Duration::from_millis(100); /// assert_eq!(Err(RecvTimeoutError::Timeout), rx.recv_timeout(timeout)); /// ``` pub fn recv_timeout(&mut self, timeout: time::Duration) -> Result<T, mpsc::RecvTimeoutError> { self.recv_inner(RecvCondition::Timeout(timeout)) } } impl<T> BusReader<T> { /// Returns an iterator that will block waiting for broadcasts. /// It will return None when the bus has been closed (i.e., the `Bus` has been dropped). pub fn iter<'a>(&'a mut self) -> BusIter<'a, T> { BusIter(self) } } impl<T> Drop for BusReader<T> { #[allow(unused_must_use)] fn drop(&mut self) { // we allow not checking the result here because the writer might have gone away, which // would result in an error, but is okay nonetheless. self.leaving.send(self.head); } } #[cfg(feature = "async")] impl<T: Clone + Sync> futures::Stream for BusReader<T> { type Item = T; type Error = void::Void; fn poll(&mut self) -> futures::Poll<Option<Self::Item>, Self::Error> { match self.try_recv() { Ok(value) => Ok(futures::Async::Ready(Some(value))), Err(mpsc::TryRecvError::Disconnected) => Ok(futures::Async::Ready(None)), Err(mpsc::TryRecvError::Empty) => Ok(futures::Async::NotReady), } } } /// An iterator over messages on a receiver. /// This iterator will block whenever `next` is called, waiting for a new message, and `None` will /// be returned when the corresponding channel has been closed. pub struct BusIter<'a, T: 'a>(&'a mut BusReader<T>); /// An owning iterator over messages on a receiver. /// This iterator will block whenever `next` is called, waiting for a new message, and `None` will /// be returned when the corresponding bus has been closed. pub struct BusIntoIter<T>(BusReader<T>); impl<'a, T: Clone + Sync> IntoIterator for &'a mut BusReader<T> { type Item = T; type IntoIter = BusIter<'a, T>; fn into_iter(self) -> BusIter<'a, T> { BusIter(self) } } impl<T: Clone + Sync> IntoIterator for BusReader<T> { type Item = T; type IntoIter = BusIntoIter<T>; fn into_iter(self) -> BusIntoIter<T> { BusIntoIter(self) } } impl<'a, T: Clone + Sync> Iterator for BusIter<'a, T> { type Item = T; fn next(&mut self) -> Option<T> { self.0.recv().ok() } } impl<T: Clone + Sync> Iterator for BusIntoIter<T> { type Item = T; fn next(&mut self) -> Option<T> { self.0.recv().ok() } } #[cfg(feature = "bench")] #[bench] fn bench_bus_one_to_one(b: &mut test::Bencher) { let mut c = Bus::new(100); let mut rx = c.add_rx(); let j = thread::spawn(move || loop { match rx.recv() { Ok(exit) if exit => break, Err(..) => break, _ => (), } }); b.iter(|| c.broadcast(false)); c.broadcast(true); j.join().unwrap(); } #[cfg(feature = "bench")] #[bench] fn bench_syncch_one_to_one(b: &mut test::Bencher) { let (tx, rx) = mpsc::sync_channel(100); let j = thread::spawn(move || loop { match rx.recv() { Ok(exit) if exit => break, Err(..) => break, _ => (), } }); b.iter(|| tx.send(false).unwrap()); tx.send(true).unwrap(); j.join().unwrap(); }