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//! An unbounded lock-free Queue //! //! # Example //! ``` //! use nolock::queues::spsc::unbounded; //! //! // Create a new UnboundedQueue //! let (mut rx, mut tx) = unbounded::queue(); //! //! // Enqueue 13 //! tx.enqueue(13); //! // Dequeue the 13 again //! assert_eq!(Ok(13), rx.try_dequeue()); //! ``` //! //! # Reference: //! * [An Efficient Unbounded Lock-Free Queue - for Multi-core Systems](https://link.springer.com/content/pdf/10.1007%2F978-3-642-32820-6_65.pdf) mod d_spsc; use std::{ fmt::Debug, sync::{atomic, Arc}, }; use super::{bounded, DequeueError, EnqueueError}; #[cfg(feature = "async")] mod async_queue; #[cfg(feature = "async")] pub use async_queue::*; // TODO // Add Support for the Caches to improve the Performance and reduce the overhead // of the Allocator /// The Sender-Half of an unbounded Queue pub struct UnboundedSender<T> { /// Indicates if the Queue has been closed or not closed: Arc<atomic::AtomicBool>, /// The Size of each Buffer buffer_size: usize, /// The current Buffer, where we insert entries buf_w: bounded::BoundedSender<T>, /// This is used to inform the Consumer aboutu any new Buffers we allocate /// in case the current one becomes full inuse_sender: d_spsc::UnboundedSender<bounded::BoundedReceiver<T>>, } impl<T> UnboundedSender<T> { /// Checks if the Queue has been closed by the Consumer /// /// # Example /// ``` /// # use nolock::queues::spsc::unbounded; /// let (rx, tx) = unbounded::queue::<usize>(); /// /// // Drop the Consumer and therefore also close the Queue /// drop(rx); /// /// assert_eq!(true, tx.is_closed()); /// ``` pub fn is_closed(&self) -> bool { self.closed.load(atomic::Ordering::Acquire) } /// Creates a new BoundedQueue and sends the Receiving half of the new /// BoundedQueue to the Consumer, using the `inuse_sender`. fn next_w(&mut self) -> bounded::BoundedSender<T> { // Creates the new BoundedQueue with the configured BufferSize let (rx, tx) = bounded::queue(self.buffer_size); // Sends the Receiving half of the newly created BoundedQueue to the // Consumer half self.inuse_sender.enqueue(rx).unwrap(); // Return the sending Half to the caller tx } /// Enqueues the Data /// /// # Example /// Normal Enqueue, where the Queue is not closed /// ``` /// # use nolock::queues::spsc::unbounded; /// let (rx, mut tx) = unbounded::queue::<usize>(); /// /// assert_eq!(Ok(()), tx.enqueue(13)); /// /// # drop(rx); /// ``` /// /// Failed Enqueue, the Queue has been closed /// ``` /// # use nolock::queues::spsc::unbounded; /// # use nolock::queues::spsc::EnqueueError; /// let (rx, mut tx) = unbounded::queue::<usize>(); /// /// // Drop the Consumer and therefore also close the Queue /// drop(rx); /// /// assert_eq!(Err((13, EnqueueError::Closed)), tx.enqueue(13)); /// ``` pub fn enqueue(&mut self, data: T) -> Result<(), (T, EnqueueError)> { if self.is_closed() { return Err((data, EnqueueError::Closed)); } // Attempt to enqueue the Data into the current BoundedQueue. // // NOTE: // We first assume that the current BoundedQueue has still room as this // will be the case most of the Time and therefore helps to reduce // the time taken for the "fastest hot path" without impacting the // alternative very much // // If this fails, we know that the BoundedQueue has to be full and // therefore we start the process to create a new Buffer if let Err((data, _)) = self.buf_w.try_enqueue(data) { // Create new BoundedQueue and set it as the current BoundedQueue // to use for any other writes/enqueues self.buf_w = self.next_w(); // Retry the Enqueue operation with the new BoundedQueue // // This should always succeed because we just now created the // BoundedQueue meaning that is still empty if self.buf_w.try_enqueue(data).is_err() { panic!("The new Buffer is always empty"); } } Ok(()) } } impl<T> Debug for UnboundedSender<T> { fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result { write!(f, "UnboundedSender ()") } } impl<T> Drop for UnboundedSender<T> { fn drop(&mut self) { self.closed.store(true, atomic::Ordering::Release); } } unsafe impl<T> Send for UnboundedSender<T> {} unsafe impl<T> Sync for UnboundedSender<T> {} /// The Receiver-Half of an unbounded Queue pub struct UnboundedReceiver<T> { /// Indicates if the Queue has been closed or not closed: Arc<atomic::AtomicBool>, /// The current BoundedQueue from which items are being Dequeued buf_r: bounded::BoundedReceiver<T>, /// This is used to receive information about any new BoundedQueues created /// by the sending Half of this Queue inuse_recv: d_spsc::UnboundedReceiver<bounded::BoundedReceiver<T>>, } impl<T> UnboundedReceiver<T> { /// Checks if the Queue has been closed by the Producer /// /// # Example /// ``` /// # use nolock::queues::spsc::unbounded; /// let (rx, tx) = unbounded::queue::<usize>(); /// /// // Dropping the Producer and therefore closing the Queue /// drop(tx); /// /// assert_eq!(true, rx.is_closed()); /// ``` pub fn is_closed(&self) -> bool { self.buf_r.is_closed() && !self.inuse_recv.has_next() } /// Attempts to dequeue a single Element from the Queue /// /// # Example /// Successful Dequeue /// ``` /// # use nolock::queues::spsc::unbounded; /// let (mut rx, mut tx) = unbounded::queue::<usize>(); /// /// tx.enqueue(13).unwrap(); /// /// assert_eq!(Ok(13), rx.try_dequeue()); /// ``` /// /// Dequeue on empty Queue /// ``` /// # use nolock::queues::spsc::unbounded; /// # use nolock::queues::spsc::DequeueError; /// let (mut rx, mut tx) = unbounded::queue::<usize>(); /// /// assert_eq!(Err(DequeueError::WouldBlock), rx.try_dequeue()); /// /// # drop(tx); /// ``` pub fn try_dequeue(&mut self) -> Result<T, DequeueError> { // Attempt to Dequeue an element from the current BoundedQueue match self.buf_r.try_dequeue() { // If we dequeued an Item, simply return that and we are done Ok(d) => Ok(d), // If we receive this Error, we know that the Queue is empty, but // the Producer has not moved on to another Queue, as it would then // be considered Closed and would return a different Error Err(DequeueError::WouldBlock) => Err(DequeueError::WouldBlock), // This indicates that the Producer has dropped the current Queue, // which indicates that they either moved on to a new Queue already, // as this one had been completly filled before, or that the entire // Producer has been dropped. // // We therefore attempt to get the Next queue, to which the // Producer would have moved on Err(DequeueError::Closed) => match self.inuse_recv.try_dequeue() { // If we find a new Queue, we can simply replace our old one // with the new one and then attempt to Dequeue th first // Element of it as our result Ok(n_queue) => { self.buf_r = n_queue; self.buf_r.try_dequeue() } // If we cant find a new Queue, that means that the Producer // has been closed and therefore the entire Queue is now also // closed as there are no more Entries left in the Queue Err(_) => Err(DequeueError::Closed), }, } } /// A simple blocking dequeue operation. This is not lock-free anymore /// (obviously) and simply spins while trying to dequeue an element from /// the Queue until it succeeds pub fn dequeue(&mut self) -> Option<T> { loop { match self.try_dequeue() { Ok(d) => return Some(d), Err(e) => match e { DequeueError::WouldBlock => {} DequeueError::Closed => return None, }, }; } } } impl<T> Debug for UnboundedReceiver<T> { fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result { write!(f, "UnboundedReceiver ()") } } impl<T> Drop for UnboundedReceiver<T> { fn drop(&mut self) { self.closed.store(true, atomic::Ordering::Release); } } unsafe impl<T> Send for UnboundedReceiver<T> {} unsafe impl<T> Sync for UnboundedReceiver<T> {} /// Creates a new Queue pub fn queue<T>() -> (UnboundedReceiver<T>, UnboundedSender<T>) { let buffer_size = 64; let (inuse_rx, inuse_tx) = d_spsc::unbounded_basic_queue(); let (initial_rx, initial_tx) = bounded::queue(buffer_size); let closed = Arc::new(atomic::AtomicBool::new(false)); ( UnboundedReceiver { closed: closed.clone(), buf_r: initial_rx, inuse_recv: inuse_rx, }, UnboundedSender { closed, buffer_size, buf_w: initial_tx, inuse_sender: inuse_tx, }, ) } #[cfg(test)] mod tests { use super::*; #[test] fn enqueue_dequeue() { let (mut rx, mut tx) = queue(); tx.enqueue(13).unwrap(); assert_eq!(Ok(13), rx.try_dequeue()); } #[test] fn multi_buffer() { let (mut rx, mut tx) = queue(); tx.enqueue(13).unwrap(); tx.enqueue(14).unwrap(); tx.enqueue(15).unwrap(); assert_eq!(Ok(13), rx.try_dequeue()); assert_eq!(Ok(14), rx.try_dequeue()); assert_eq!(Ok(15), rx.try_dequeue()); } #[test] fn enqueue_closed() { let (rx, mut tx) = queue(); drop(rx); assert_eq!(Err((13, EnqueueError::Closed)), tx.enqueue(13)); } #[test] fn dequeue_closed() { let (mut rx, tx) = queue::<usize>(); drop(tx); assert_eq!(Err(DequeueError::Closed), rx.try_dequeue()); } }