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//! An asynchronously awaitable multi producer multi consumer channel use core::marker::PhantomData; use futures_core::task::{Context, Poll}; use lock_api::{RawMutex, Mutex}; use crate::{NoopLock, buffer::{RingBuf, ArrayRingBuf}}; use crate::intrusive_singly_linked_list::{LinkedList, ListNode}; use super::{ RecvPollState, RecvWaitQueueEntry, SendPollState, SendWaitQueueEntry, ChannelReceiveAccess, ChannelReceiveFuture, ChannelSendAccess, ChannelSendFuture, }; fn wake_recv_waiters(mut waiters: LinkedList<RecvWaitQueueEntry>) { unsafe { // Reverse the waiter list, so that the oldest waker (which is // at the end of the list), gets woken first and has the best // chance to grab the channel value. waiters.reverse(); for waiter in waiters.into_iter() { if let Some(handle) = (*waiter).task.take() { handle.wake(); } // The only kind of waiter that could have been stored here are // registered waiters (with a value), since others are removed // whenever their value had been copied into the channel. (*waiter).state = RecvPollState::Unregistered; } } } fn wake_send_waiters<T>(mut waiters: LinkedList<SendWaitQueueEntry<T>>) { unsafe { // Reverse the waiter list, so that the oldest waker (which is // at the end of the list), gets woken first and has the best // chance to grab the channel value. waiters.reverse(); for waiter in waiters.into_iter() { if let Some(handle) = (*waiter).task.take() { handle.wake(); } (*waiter).state = SendPollState::Unregistered; } } } /// Wakes up the last waiter and removes it from the wait queue fn wakeup_last_receive_waiter(waiters: &mut LinkedList<RecvWaitQueueEntry>) { let last_waiter = waiters.remove_last(); if !last_waiter.is_null() { unsafe { (*last_waiter).state = RecvPollState::Notified; if let Some(handle) = (*last_waiter).task.take() { handle.wake(); } } } } /// Internal state of the channel struct ChannelState<T, A> where A: RingBuf<Item=T> { /// Whether the channel had been closed is_closed: bool, /// The value which is stored inside the channel buffer: A, /// Futures which are blocked on receive receive_waiters: LinkedList<RecvWaitQueueEntry>, /// Futures which are blocked on send send_waiters: LinkedList<SendWaitQueueEntry<T>>, } impl<T, A> ChannelState<T, A> where A: RingBuf<Item=T> { fn new(buffer: A) -> ChannelState<T, A> { ChannelState::<T, A> { is_closed: false, buffer, receive_waiters: LinkedList::new(), send_waiters: LinkedList::new(), } } fn close(&mut self) { if self.is_closed { return; } self.is_closed = true; // Wakeup all send and receive waiters, since they are now guaranteed // to make progress. let recv_waiters = self.receive_waiters.take(); wake_recv_waiters(recv_waiters); let send_waiters = self.send_waiters.take(); wake_send_waiters(send_waiters); } /// Tries to send a value to the channel. /// If the value isn't available yet, the ChannelSendFuture gets added to the /// wait queue at the channel, and will be signalled once ready. /// If the channels is already closed, the value to send is returned. /// This function is only safe as long as the `wait_node`s address is guaranteed /// to be stable until it gets removed from the queue. unsafe fn try_send( &mut self, wait_node: &mut ListNode<SendWaitQueueEntry<T>>, cx: &mut Context<'_>, ) -> (Poll<()>, Option<T>) { match wait_node.state { SendPollState::Unregistered => { if self.is_closed { let value = wait_node.value.take(); return (Poll::Ready(()), value); } if !self.buffer.can_push() { // If the capacity is exhausted, register a waiter wait_node.task = Some(cx.waker().clone()); wait_node.state = SendPollState::Registered; self.send_waiters.add_front(wait_node); // Wakeup the oldest receive waiter wakeup_last_receive_waiter(&mut self.receive_waiters); return (Poll::Pending, None); } else { // Otherwise copy the value directly into the channel let value = wait_node.value.take().expect( "wait_node must contain value"); self.buffer.push(value); // Wakeup the oldest receive waiter wakeup_last_receive_waiter(&mut self.receive_waiters); (Poll::Ready(()), None) } }, SendPollState::Registered => { // Since the channel wakes up all waiters and moves their states to unregistered // there can't be space available in the channel. (Poll::Pending, None) }, SendPollState::SendComplete => { // The transfer is complete, and the sender has already been removed from the // list of pending senders (Poll::Ready(()), None) }, } } /// If there is a send waiter, copy it's value into the channel buffer and complete it. /// The method may only be called if there is space in the receive buffer. unsafe fn try_copy_value_from_last_waiter(&mut self) { let last_waiter = self.send_waiters.remove_last(); if !last_waiter.is_null() { let last_waiter = &mut(*last_waiter); let value = last_waiter.value.take().expect( "wait_node must contain value"); self.buffer.push(value); last_waiter.state = SendPollState::SendComplete; if let Some(ref handle) = &last_waiter.task { handle.wake_by_ref(); } } } /// Tries to read the value from the channel. /// If the value isn't available yet, the ChannelReceiveFuture gets added to the /// wait queue at the channel, and will be signalled once ready. /// This function is only safe as long as the `wait_node`s address is guaranteed /// to be stable until it gets removed from the queue. unsafe fn try_receive( &mut self, wait_node: &mut ListNode<RecvWaitQueueEntry>, cx: &mut Context<'_>, ) -> Poll<Option<T>> { match wait_node.state { RecvPollState::Unregistered | RecvPollState::Notified => { wait_node.state = RecvPollState::Unregistered; if !self.buffer.is_empty() { // A value is available - grab it. let val = self.buffer.pop(); // Since this means a space in the buffer had been freed, // try to copy a value from a potential waiter into the channel. self.try_copy_value_from_last_waiter(); Poll::Ready(Some(val)) } else if !self.send_waiters.is_empty() { // This path should be only used for 0 capacity queues. // Since the list is not empty, a value is available. // Extract it from the sender in order to return it assert_eq!(0, self.buffer.capacity()); let last_sender = self.send_waiters.remove_last(); assert!(!last_sender.is_null()); // Safety: The sender can't be null, since we only add valid // senders to the queue let last_sender = &mut (*last_sender); let val = last_sender.value.take().expect( "Value must be available"); last_sender.state = SendPollState::SendComplete; // Wakeup the waiter if let Some(ref task) = &last_sender.task { task.wake_by_ref(); } Poll::Ready(Some(val)) } else if self.is_closed { Poll::Ready(None) } else { // Added the task to the wait queue wait_node.task = Some(cx.waker().clone()); wait_node.state = RecvPollState::Registered; self.receive_waiters.add_front(wait_node); Poll::Pending } }, RecvPollState::Registered => { // Since the channel wakes up all waiters and moves their states // to unregistered there can't be any value in the channel in // this state. Poll::Pending }, } } fn remove_send_waiter(&mut self, wait_node: &mut ListNode<SendWaitQueueEntry<T>>) { // ChannelSendFuture only needs to get removed if it had been added to // the wait queue of the channel. // This has happened in the SendPollState::Registered case. match wait_node.state { SendPollState::Registered => { if ! unsafe { self.send_waiters.remove(wait_node) } { // Panic if the address isn't found. This can only happen if the contract was // violated, e.g. the WaitQueueEntry got moved after the initial poll. panic!("Future could not be removed from wait queue"); } wait_node.state = SendPollState::Unregistered; }, SendPollState::Unregistered => { }, SendPollState::SendComplete => { // Send was complete. In that case the queue item is not in the list }, } } fn remove_receive_waiter(&mut self, wait_node: &mut ListNode<RecvWaitQueueEntry>) { // ChannelReceiveFuture only needs to get removed if it had been added to // the wait queue of the channel. This has happened in the RecvPollState::Registered case. match wait_node.state { RecvPollState::Registered => { if ! unsafe { self.receive_waiters.remove(wait_node) } { // Panic if the address isn't found. This can only happen if the contract was // violated, e.g. the WaitQueueEntry got moved after the initial poll. panic!("Future could not be removed from wait queue"); } wait_node.state = RecvPollState::Unregistered; }, RecvPollState::Notified => { // wakeup another receive waiter instead wakeup_last_receive_waiter(&mut self.receive_waiters); wait_node.state = RecvPollState::Unregistered; }, RecvPollState::Unregistered => { }, } } } /// A channel which can be used to exchange values of type `T` between /// concurrent tasks. /// /// `A` represents the backing buffer for a Channel. E.g. a channel which /// can buffer up to 4 u32 values can be created via: /// /// ``` /// # use futures_intrusive::channel::LocalChannel; /// let channel: LocalChannel<i32, [i32; 4]> = LocalChannel::new(); /// ``` /// /// Tasks can receive values from the channel through the `receive` method. /// The returned Future will get resolved when a value is sent into the channel. /// Values can be sent into the channel through `send`. /// The returned Future will get resolved when the value has been stored /// inside the channel. pub struct GenericChannel<MutexType: RawMutex, T, A> where A: RingBuf<Item=T> { inner: Mutex<MutexType, ChannelState<T, A>>, } // The channel can be sent to other threads as long as it's not borrowed and the // value in it can be sent to other threads. unsafe impl<MutexType: RawMutex + Send, T: Send, A> Send for GenericChannel<MutexType, T, A> where A: RingBuf<Item=T> + Send {} // The channel is thread-safe as long as a thread-safe mutex is used unsafe impl<MutexType: RawMutex + Sync, T: Send, A> Sync for GenericChannel<MutexType, T, A> where A: RingBuf<Item=T> {} impl<MutexType: RawMutex, T, A> core::fmt::Debug for GenericChannel<MutexType, T, A> where A: RingBuf<Item=T> { fn fmt(&self, f: &mut core::fmt::Formatter) -> core::fmt::Result { f.debug_struct("Channel") .finish() } } impl<MutexType: RawMutex, T, A> GenericChannel<MutexType, T, A> where A: RingBuf<Item=T> { /// Creates a new Channel, utilizing the default capacity that /// the RingBuffer in `A` provides. pub fn new() -> Self { GenericChannel { inner: Mutex::new(ChannelState::new(A::new())), } } /// Creates a new Channel, which has storage for a `capacity` items. /// Depending on the utilized `RingBuf` type, the capacity argument might /// be ignored and the default capacity might be utilized. pub fn with_capacity(capacity: usize) -> Self { GenericChannel { inner: Mutex::new(ChannelState::new(A::with_capacity(capacity))), } } /// Returns a future that gets fulfilled when the value has been written to /// the channel. /// If the channel gets closed while the send is in progress, sending the /// value will fail, and the future will deliver the value back. pub fn send(&self, value: T) -> ChannelSendFuture<MutexType, T> { ChannelSendFuture { channel: Some(self), wait_node: ListNode::new(SendWaitQueueEntry::new(value)), _phantom: PhantomData, } } /// Returns a future that gets fulfilled when a value is written to the channel. /// If the channels gets closed, the future will resolve to `None`. pub fn receive(&self) -> ChannelReceiveFuture<MutexType, T> { ChannelReceiveFuture { channel: Some(self), wait_node: ListNode::new(RecvWaitQueueEntry::new()), _phantom: PhantomData, } } /// Closes the channel. /// All pending and future send attempts will fail. /// Receive attempts will continue to succeed as long as there are items /// stored inside the channel. Further attempts will fail. pub fn close(&self) { self.inner.lock().close() } } impl <MutexType: RawMutex, T, A> ChannelSendAccess<T> for GenericChannel<MutexType, T, A> where A: RingBuf<Item=T> { unsafe fn try_send( &self, wait_node: &mut ListNode<SendWaitQueueEntry<T>>, cx: &mut Context<'_>, ) -> (Poll<()>, Option<T>) { self.inner.lock().try_send(wait_node, cx) } fn remove_send_waiter(&self, wait_node: &mut ListNode<SendWaitQueueEntry<T>>) { self.inner.lock().remove_send_waiter(wait_node) } } impl <MutexType: RawMutex, T, A> ChannelReceiveAccess<T> for GenericChannel<MutexType, T, A> where A: RingBuf<Item=T> { unsafe fn try_receive( &self, wait_node: &mut ListNode<RecvWaitQueueEntry>, cx: &mut Context<'_>, ) -> Poll<Option<T>> { self.inner.lock().try_receive(wait_node, cx) } fn remove_receive_waiter(&self, wait_node: &mut ListNode<RecvWaitQueueEntry>) { self.inner.lock().remove_receive_waiter(wait_node) } } // Export a non thread-safe version using NoopLock /// A [`GenericChannel`] implementation which is not thread-safe. pub type LocalChannel<T, A> = GenericChannel<NoopLock, T, ArrayRingBuf<T, A>>; /// An unbuffered [`GenericChannel`] implementation which is not thread-safe. pub type LocalUnbufferedChannel<T> = LocalChannel<T, [T; 0]>; #[cfg(feature = "std")] mod if_std { use super::*; // Export a thread-safe version using parking_lot::RawMutex // TODO: We might also want to bind Channel to GenericChannel<..., HeapRingBuf>, // which performs less type-churn. // However since we can't bind LocalChannel to that too due to no-std compatibility, // this would to introduce some inconsistency between those types. // It's also bit unfortunate that there are now `new()` and `with_capacity` // methods on both types, but for the array backed implementation only // `new()` is meaningful, while for the heap backed implementation only // `with_capacity()` is meaningful. /// A [`GenericChannel`] implementation backed by [`parking_lot`]. pub type Channel<T, A> = GenericChannel<parking_lot::RawMutex, T, ArrayRingBuf<T, A>>; /// An unbuffered [`GenericChannel`] implementation backed by [`parking_lot`]. pub type UnbufferedChannel<T> = Channel<T, [T; 0]>; } #[cfg(feature = "std")] pub use self::if_std::*; // The next section should really integrated if the alloc feature is active, // since it mainly requires `Arc` to be available. However for simplicity reasons // it is currently only activated in std environments. #[cfg(feature = "std")] mod if_alloc { use super::*; /// Channel implementations where Sender and Receiver sides are cloneable /// and owned. /// The Futures produced by channels in this module don't require a lifetime /// parameter. pub mod shared { use super::*; use crate::buffer::HeapRingBuf; use crate::channel::shared::{ChannelReceiveFuture, ChannelSendFuture}; use std::sync::atomic::{AtomicUsize, Ordering}; /// Shared Channel State, which is referenced by Senders and Receivers struct GenericChannelSharedState<MutexType, T> where MutexType: RawMutex , T: 'static { /// The amount of [`GenericSender`] instances which reference this state. senders: AtomicUsize, /// The amount of [`GenericReceiver`] instances which reference this state. receivers: AtomicUsize, /// The channel on which is acted. channel: GenericChannel<MutexType, T, HeapRingBuf<T>>, } // Implement ChannelAccess trait for SharedChannelState, so that it can // be used for dynamic dispatch in futures. impl <MutexType, T> ChannelReceiveAccess<T> for GenericChannelSharedState<MutexType, T> where MutexType: RawMutex { unsafe fn try_receive( &self, wait_node: &mut ListNode<RecvWaitQueueEntry>, cx: &mut Context<'_>, ) -> Poll<Option<T>> { self.channel.try_receive(wait_node, cx) } fn remove_receive_waiter(&self, wait_node: &mut ListNode<RecvWaitQueueEntry>) { self.channel.remove_receive_waiter(wait_node) } } // Implement ChannelAccess trait for SharedChannelState, so that it can // be used for dynamic dispatch in futures. impl <MutexType, T> ChannelSendAccess<T> for GenericChannelSharedState<MutexType, T> where MutexType: RawMutex { unsafe fn try_send( &self, wait_node: &mut ListNode<SendWaitQueueEntry<T>>, cx: &mut Context<'_>, ) -> (Poll<()>, Option<T>) { self.channel.try_send(wait_node, cx) } fn remove_send_waiter(&self, wait_node: &mut ListNode<SendWaitQueueEntry<T>>) { self.channel.remove_send_waiter(wait_node) } } /// The sending side of a channel which can be used to exchange values /// between concurrent tasks. /// /// Values can be sent into the channel through `send`. /// The returned Future will get resolved when the value has been stored inside the channel. pub struct GenericSender<MutexType, T> where MutexType: RawMutex , T: 'static { inner: std::sync::Arc<GenericChannelSharedState<MutexType, T>>, } /// The receiving side of a channel which can be used to exchange values /// between concurrent tasks. /// /// Tasks can receive values from the channel through the `receive` method. /// The returned Future will get resolved when a value is sent into the channel. pub struct GenericReceiver<MutexType, T> where MutexType: RawMutex , T: 'static { inner: std::sync::Arc<GenericChannelSharedState<MutexType, T>>, } impl<MutexType, T> core::fmt::Debug for GenericSender<MutexType, T> where MutexType: RawMutex { fn fmt(&self, f: &mut core::fmt::Formatter) -> core::fmt::Result { f.debug_struct("Sender") .finish() } } impl<MutexType, T> core::fmt::Debug for GenericReceiver<MutexType, T> where MutexType: RawMutex { fn fmt(&self, f: &mut core::fmt::Formatter) -> core::fmt::Result { f.debug_struct("Receiver") .finish() } } impl<MutexType, T> Clone for GenericSender<MutexType, T> where MutexType: RawMutex { fn clone(&self) -> Self { let old_size = self.inner.senders.fetch_add(1, Ordering::Relaxed); if old_size > (core::isize::MAX) as usize { panic!("Reached maximum refcount"); } GenericSender { inner: self.inner.clone(), } } } impl<MutexType, T> Drop for GenericSender<MutexType, T> where MutexType: RawMutex { fn drop(&mut self) { if self.inner.senders.fetch_sub(1, Ordering::Release) != 1 { return; } std::sync::atomic::fence(Ordering::Acquire); // Close the channel, before last sender gets destroyed // TODO: We could potentially avoid this, if no receiver is left self.inner.channel.close(); } } impl<MutexType, T> Clone for GenericReceiver<MutexType, T> where MutexType: RawMutex { fn clone(&self) -> Self { let old_size = self.inner.receivers.fetch_add(1, Ordering::Relaxed); if old_size > (core::isize::MAX) as usize { panic!("Reached maximum refcount"); } GenericReceiver { inner: self.inner.clone(), } } } impl<MutexType, T> Drop for GenericReceiver<MutexType, T> where MutexType: RawMutex { fn drop(&mut self) { if self.inner.receivers.fetch_sub(1, Ordering::Release) != 1 { return; } std::sync::atomic::fence(Ordering::Acquire); // Close the channel, before last receiver gets destroyed // TODO: We could potentially avoid this, if no sender is left self.inner.channel.close(); } } /// Creates a new Channel which can be used to exchange values of type `T` between /// concurrent tasks. The ends of the Channel are represented through /// the returned Sender and Receiver. /// Both the Sender and Receiver can be cloned in order to let more tasks /// interact with the Channel. /// /// As soon es either all Senders or all Receivers are closed, the Channel /// itself will be closed. /// /// The channel can buffer up to `capacity` items internally. /// /// ``` /// # use futures_intrusive::channel::shared::channel; /// let (sender, receiver) = channel::<i32>(4); /// ``` pub fn generic_channel<MutexType, T>(capacity: usize) -> (GenericSender<MutexType, T>, GenericReceiver<MutexType, T>) where MutexType: RawMutex, T: Send { let inner = std::sync::Arc::new( GenericChannelSharedState { channel: GenericChannel::with_capacity(capacity), senders: AtomicUsize::new(1), receivers: AtomicUsize::new(1), }); let sender = GenericSender { inner: inner.clone(), }; let receiver = GenericReceiver { inner, }; (sender, receiver) } impl<MutexType, T> GenericSender<MutexType, T> where MutexType: RawMutex + 'static { /// Returns a future that gets fulfilled when the value has been written to /// the channel. /// If the channel gets closed while the send is in progress, sending the /// value will fail, and the future will deliver the value back. pub fn send(&self, value: T) -> ChannelSendFuture<MutexType, T> { ChannelSendFuture { channel: Some(self.inner.clone()), wait_node: ListNode::new(SendWaitQueueEntry::new(value)), _phantom: PhantomData, } } /// Closes the channel. /// All pending future send attempts will fail. /// Receive attempts will continue to succeed as long as there are items /// stored inside the channel. Further attempts will return `None`. pub fn close(&self) { self.inner.channel.close() } } impl<MutexType, T> GenericReceiver<MutexType, T> where MutexType: RawMutex + 'static { /// Returns a future that gets fulfilled when a value is written to the channel. /// If the channels gets closed, the future will resolve to `None`. pub fn receive(&self) -> ChannelReceiveFuture<MutexType, T> { ChannelReceiveFuture { channel: Some(self.inner.clone()), wait_node: ListNode::new(RecvWaitQueueEntry::new()), _phantom: PhantomData, } } /// Closes the channel. /// All pending future send attempts will fail. /// Receive attempts will continue to succeed as long as there are items /// stored inside the channel. Further attempts will return `None`. pub fn close(&self) { self.inner.channel.close() } } // Export parking_lot based shared channels in std mode #[cfg(feature = "std")] mod if_std { use super::*; /// A [`GenericSender`] implementation backed by [`parking_lot`]. pub type Sender<T> = GenericSender<parking_lot::RawMutex, T>; /// A [`GenericReceiver`] implementation backed by [`parking_lot`]. pub type Receiver<T> = GenericReceiver<parking_lot::RawMutex, T>; /// Creates a new channel. /// /// Refer to [`generic_channel`] for details. pub fn channel<T>(capacity: usize) -> (Sender<T>, Receiver<T>) where T: Send { generic_channel::<parking_lot::RawMutex, T>(capacity) } /// A [`GenericSender`] implementation backed by [`parking_lot`]. pub type UnbufferedSender<T> = GenericSender<parking_lot::RawMutex, T>; /// A [`GenericReceiver`] implementation backed by [`parking_lot`]. pub type UnbufferedReceiver<T> = GenericReceiver<parking_lot::RawMutex, T>; /// Creates a new unbuffered channel. /// /// Refer to [`generic_channel`] for details. pub fn unbuffered_channel<T>() -> (Sender<T>, Receiver<T>) where T: Send { generic_channel::<parking_lot::RawMutex, T>(0) } } #[cfg(feature = "std")] pub use self::if_std::*; } } #[cfg(feature = "std")] pub use self::if_alloc::*;