Adding upstream version 1:115.7.0.upstream/1%115.7.0upstream

Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>

1 files changed, 547 insertions, 0 deletions

diff --git a/third_party/rust/crossbeam-queue/src/seg_queue.rs b/third_party/rust/crossbeam-queue/src/seg_queue.rs
new file mode 100644
index 0000000000..2761dc07cd
--- /dev/null
+++ b/third_party/rust/crossbeam-queue/src/seg_queue.rs
@@ -0,0 +1,547 @@
+use alloc::boxed::Box;
+use core::cell::UnsafeCell;
+use core::fmt;
+use core::marker::PhantomData;
+use core::mem::MaybeUninit;
+use core::ptr;
+use core::sync::atomic::{self, AtomicPtr, AtomicUsize, Ordering};
+
+use crossbeam_utils::{Backoff, CachePadded};
+
+// Bits indicating the state of a slot:
+// * If a value has been written into the slot, `WRITE` is set.
+// * If a value has been read from the slot, `READ` is set.
+// * If the block is being destroyed, `DESTROY` is set.
+const WRITE: usize = 1;
+const READ: usize = 2;
+const DESTROY: usize = 4;
+
+// Each block covers one "lap" of indices.
+const LAP: usize = 32;
+// The maximum number of values a block can hold.
+const BLOCK_CAP: usize = LAP - 1;
+// How many lower bits are reserved for metadata.
+const SHIFT: usize = 1;
+// Indicates that the block is not the last one.
+const HAS_NEXT: usize = 1;
+
+/// A slot in a block.
+struct Slot<T> {
+    /// The value.
+    value: UnsafeCell<MaybeUninit<T>>,
+
+    /// The state of the slot.
+    state: AtomicUsize,
+}
+
+impl<T> Slot<T> {
+    const UNINIT: Self = Self {
+        value: UnsafeCell::new(MaybeUninit::uninit()),
+        state: AtomicUsize::new(0),
+    };
+
+    /// Waits until a value is written into the slot.
+    fn wait_write(&self) {
+        let backoff = Backoff::new();
+        while self.state.load(Ordering::Acquire) & WRITE == 0 {
+            backoff.snooze();
+        }
+    }
+}
+
+/// A block in a linked list.
+///
+/// Each block in the list can hold up to `BLOCK_CAP` values.
+struct Block<T> {
+    /// The next block in the linked list.
+    next: AtomicPtr<Block<T>>,
+
+    /// Slots for values.
+    slots: [Slot<T>; BLOCK_CAP],
+}
+
+impl<T> Block<T> {
+    /// Creates an empty block that starts at `start_index`.
+    fn new() -> Block<T> {
+        Self {
+            next: AtomicPtr::new(ptr::null_mut()),
+            slots: [Slot::UNINIT; BLOCK_CAP],
+        }
+    }
+
+    /// Waits until the next pointer is set.
+    fn wait_next(&self) -> *mut Block<T> {
+        let backoff = Backoff::new();
+        loop {
+            let next = self.next.load(Ordering::Acquire);
+            if !next.is_null() {
+                return next;
+            }
+            backoff.snooze();
+        }
+    }
+
+    /// Sets the `DESTROY` bit in slots starting from `start` and destroys the block.
+    unsafe fn destroy(this: *mut Block<T>, start: usize) {
+        // It is not necessary to set the `DESTROY` bit in the last slot because that slot has
+        // begun destruction of the block.
+        for i in start..BLOCK_CAP - 1 {
+            let slot = (*this).slots.get_unchecked(i);
+
+            // Mark the `DESTROY` bit if a thread is still using the slot.
+            if slot.state.load(Ordering::Acquire) & READ == 0
+                && slot.state.fetch_or(DESTROY, Ordering::AcqRel) & READ == 0
+            {
+                // If a thread is still using the slot, it will continue destruction of the block.
+                return;
+            }
+        }
+
+        // No thread is using the block, now it is safe to destroy it.
+        drop(Box::from_raw(this));
+    }
+}
+
+/// A position in a queue.
+struct Position<T> {
+    /// The index in the queue.
+    index: AtomicUsize,
+
+    /// The block in the linked list.
+    block: AtomicPtr<Block<T>>,
+}
+
+/// An unbounded multi-producer multi-consumer queue.
+///
+/// This queue is implemented as a linked list of segments, where each segment is a small buffer
+/// that can hold a handful of elements. There is no limit to how many elements can be in the queue
+/// at a time. However, since segments need to be dynamically allocated as elements get pushed,
+/// this queue is somewhat slower than [`ArrayQueue`].
+///
+/// [`ArrayQueue`]: super::ArrayQueue
+///
+/// # Examples
+///
+/// ```
+/// use crossbeam_queue::SegQueue;
+///
+/// let q = SegQueue::new();
+///
+/// q.push('a');
+/// q.push('b');
+///
+/// assert_eq!(q.pop(), Some('a'));
+/// assert_eq!(q.pop(), Some('b'));
+/// assert!(q.pop().is_none());
+/// ```
+pub struct SegQueue<T> {
+    /// The head of the queue.
+    head: CachePadded<Position<T>>,
+
+    /// The tail of the queue.
+    tail: CachePadded<Position<T>>,
+
+    /// Indicates that dropping a `SegQueue<T>` may drop values of type `T`.
+    _marker: PhantomData<T>,
+}
+
+unsafe impl<T: Send> Send for SegQueue<T> {}
+unsafe impl<T: Send> Sync for SegQueue<T> {}
+
+impl<T> SegQueue<T> {
+    /// Creates a new unbounded queue.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// use crossbeam_queue::SegQueue;
+    ///
+    /// let q = SegQueue::<i32>::new();
+    /// ```
+    pub const fn new() -> SegQueue<T> {
+        SegQueue {
+            head: CachePadded::new(Position {
+                block: AtomicPtr::new(ptr::null_mut()),
+                index: AtomicUsize::new(0),
+            }),
+            tail: CachePadded::new(Position {
+                block: AtomicPtr::new(ptr::null_mut()),
+                index: AtomicUsize::new(0),
+            }),
+            _marker: PhantomData,
+        }
+    }
+
+    /// Pushes an element into the queue.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// use crossbeam_queue::SegQueue;
+    ///
+    /// let q = SegQueue::new();
+    ///
+    /// q.push(10);
+    /// q.push(20);
+    /// ```
+    pub fn push(&self, value: T) {
+        let backoff = Backoff::new();
+        let mut tail = self.tail.index.load(Ordering::Acquire);
+        let mut block = self.tail.block.load(Ordering::Acquire);
+        let mut next_block = None;
+
+        loop {
+            // Calculate the offset of the index into the block.
+            let offset = (tail >> SHIFT) % LAP;
+
+            // If we reached the end of the block, wait until the next one is installed.
+            if offset == BLOCK_CAP {
+                backoff.snooze();
+                tail = self.tail.index.load(Ordering::Acquire);
+                block = self.tail.block.load(Ordering::Acquire);
+                continue;
+            }
+
+            // If we're going to have to install the next block, allocate it in advance in order to
+            // make the wait for other threads as short as possible.
+            if offset + 1 == BLOCK_CAP && next_block.is_none() {
+                next_block = Some(Box::new(Block::<T>::new()));
+            }
+
+            // If this is the first push operation, we need to allocate the first block.
+            if block.is_null() {
+                let new = Box::into_raw(Box::new(Block::<T>::new()));
+
+                if self
+                    .tail
+                    .block
+                    .compare_exchange(block, new, Ordering::Release, Ordering::Relaxed)
+                    .is_ok()
+                {
+                    self.head.block.store(new, Ordering::Release);
+                    block = new;
+                } else {
+                    next_block = unsafe { Some(Box::from_raw(new)) };
+                    tail = self.tail.index.load(Ordering::Acquire);
+                    block = self.tail.block.load(Ordering::Acquire);
+                    continue;
+                }
+            }
+
+            let new_tail = tail + (1 << SHIFT);
+
+            // Try advancing the tail forward.
+            match self.tail.index.compare_exchange_weak(
+                tail,
+                new_tail,
+                Ordering::SeqCst,
+                Ordering::Acquire,
+            ) {
+                Ok(_) => unsafe {
+                    // If we've reached the end of the block, install the next one.
+                    if offset + 1 == BLOCK_CAP {
+                        let next_block = Box::into_raw(next_block.unwrap());
+                        let next_index = new_tail.wrapping_add(1 << SHIFT);
+
+                        self.tail.block.store(next_block, Ordering::Release);
+                        self.tail.index.store(next_index, Ordering::Release);
+                        (*block).next.store(next_block, Ordering::Release);
+                    }
+
+                    // Write the value into the slot.
+                    let slot = (*block).slots.get_unchecked(offset);
+                    slot.value.get().write(MaybeUninit::new(value));
+                    slot.state.fetch_or(WRITE, Ordering::Release);
+
+                    return;
+                },
+                Err(t) => {
+                    tail = t;
+                    block = self.tail.block.load(Ordering::Acquire);
+                    backoff.spin();
+                }
+            }
+        }
+    }
+
+    /// Pops an element from the queue.
+    ///
+    /// If the queue is empty, `None` is returned.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// use crossbeam_queue::SegQueue;
+    ///
+    /// let q = SegQueue::new();
+    ///
+    /// q.push(10);
+    /// assert_eq!(q.pop(), Some(10));
+    /// assert!(q.pop().is_none());
+    /// ```
+    pub fn pop(&self) -> Option<T> {
+        let backoff = Backoff::new();
+        let mut head = self.head.index.load(Ordering::Acquire);
+        let mut block = self.head.block.load(Ordering::Acquire);
+
+        loop {
+            // Calculate the offset of the index into the block.
+            let offset = (head >> SHIFT) % LAP;
+
+            // If we reached the end of the block, wait until the next one is installed.
+            if offset == BLOCK_CAP {
+                backoff.snooze();
+                head = self.head.index.load(Ordering::Acquire);
+                block = self.head.block.load(Ordering::Acquire);
+                continue;
+            }
+
+            let mut new_head = head + (1 << SHIFT);
+
+            if new_head & HAS_NEXT == 0 {
+                atomic::fence(Ordering::SeqCst);
+                let tail = self.tail.index.load(Ordering::Relaxed);
+
+                // If the tail equals the head, that means the queue is empty.
+                if head >> SHIFT == tail >> SHIFT {
+                    return None;
+                }
+
+                // If head and tail are not in the same block, set `HAS_NEXT` in head.
+                if (head >> SHIFT) / LAP != (tail >> SHIFT) / LAP {
+                    new_head |= HAS_NEXT;
+                }
+            }
+
+            // The block can be null here only if the first push operation is in progress. In that
+            // case, just wait until it gets initialized.
+            if block.is_null() {
+                backoff.snooze();
+                head = self.head.index.load(Ordering::Acquire);
+                block = self.head.block.load(Ordering::Acquire);
+                continue;
+            }
+
+            // Try moving the head index forward.
+            match self.head.index.compare_exchange_weak(
+                head,
+                new_head,
+                Ordering::SeqCst,
+                Ordering::Acquire,
+            ) {
+                Ok(_) => unsafe {
+                    // If we've reached the end of the block, move to the next one.
+                    if offset + 1 == BLOCK_CAP {
+                        let next = (*block).wait_next();
+                        let mut next_index = (new_head & !HAS_NEXT).wrapping_add(1 << SHIFT);
+                        if !(*next).next.load(Ordering::Relaxed).is_null() {
+                            next_index |= HAS_NEXT;
+                        }
+
+                        self.head.block.store(next, Ordering::Release);
+                        self.head.index.store(next_index, Ordering::Release);
+                    }
+
+                    // Read the value.
+                    let slot = (*block).slots.get_unchecked(offset);
+                    slot.wait_write();
+                    let value = slot.value.get().read().assume_init();
+
+                    // Destroy the block if we've reached the end, or if another thread wanted to
+                    // destroy but couldn't because we were busy reading from the slot.
+                    if offset + 1 == BLOCK_CAP {
+                        Block::destroy(block, 0);
+                    } else if slot.state.fetch_or(READ, Ordering::AcqRel) & DESTROY != 0 {
+                        Block::destroy(block, offset + 1);
+                    }
+
+                    return Some(value);
+                },
+                Err(h) => {
+                    head = h;
+                    block = self.head.block.load(Ordering::Acquire);
+                    backoff.spin();
+                }
+            }
+        }
+    }
+
+    /// Returns `true` if the queue is empty.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// use crossbeam_queue::SegQueue;
+    ///
+    /// let q = SegQueue::new();
+    ///
+    /// assert!(q.is_empty());
+    /// q.push(1);
+    /// assert!(!q.is_empty());
+    /// ```
+    pub fn is_empty(&self) -> bool {
+        let head = self.head.index.load(Ordering::SeqCst);
+        let tail = self.tail.index.load(Ordering::SeqCst);
+        head >> SHIFT == tail >> SHIFT
+    }
+
+    /// Returns the number of elements in the queue.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// use crossbeam_queue::SegQueue;
+    ///
+    /// let q = SegQueue::new();
+    /// assert_eq!(q.len(), 0);
+    ///
+    /// q.push(10);
+    /// assert_eq!(q.len(), 1);
+    ///
+    /// q.push(20);
+    /// assert_eq!(q.len(), 2);
+    /// ```
+    pub fn len(&self) -> usize {
+        loop {
+            // Load the tail index, then load the head index.
+            let mut tail = self.tail.index.load(Ordering::SeqCst);
+            let mut head = self.head.index.load(Ordering::SeqCst);
+
+            // If the tail index didn't change, we've got consistent indices to work with.
+            if self.tail.index.load(Ordering::SeqCst) == tail {
+                // Erase the lower bits.
+                tail &= !((1 << SHIFT) - 1);
+                head &= !((1 << SHIFT) - 1);
+
+                // Fix up indices if they fall onto block ends.
+                if (tail >> SHIFT) & (LAP - 1) == LAP - 1 {
+                    tail = tail.wrapping_add(1 << SHIFT);
+                }
+                if (head >> SHIFT) & (LAP - 1) == LAP - 1 {
+                    head = head.wrapping_add(1 << SHIFT);
+                }
+
+                // Rotate indices so that head falls into the first block.
+                let lap = (head >> SHIFT) / LAP;
+                tail = tail.wrapping_sub((lap * LAP) << SHIFT);
+                head = head.wrapping_sub((lap * LAP) << SHIFT);
+
+                // Remove the lower bits.
+                tail >>= SHIFT;
+                head >>= SHIFT;
+
+                // Return the difference minus the number of blocks between tail and head.
+                return tail - head - tail / LAP;
+            }
+        }
+    }
+}
+
+impl<T> Drop for SegQueue<T> {
+    fn drop(&mut self) {
+        let mut head = *self.head.index.get_mut();
+        let mut tail = *self.tail.index.get_mut();
+        let mut block = *self.head.block.get_mut();
+
+        // Erase the lower bits.
+        head &= !((1 << SHIFT) - 1);
+        tail &= !((1 << SHIFT) - 1);
+
+        unsafe {
+            // Drop all values between `head` and `tail` and deallocate the heap-allocated blocks.
+            while head != tail {
+                let offset = (head >> SHIFT) % LAP;
+
+                if offset < BLOCK_CAP {
+                    // Drop the value in the slot.
+                    let slot = (*block).slots.get_unchecked(offset);
+                    let p = &mut *slot.value.get();
+                    p.as_mut_ptr().drop_in_place();
+                } else {
+                    // Deallocate the block and move to the next one.
+                    let next = *(*block).next.get_mut();
+                    drop(Box::from_raw(block));
+                    block = next;
+                }
+
+                head = head.wrapping_add(1 << SHIFT);
+            }
+
+            // Deallocate the last remaining block.
+            if !block.is_null() {
+                drop(Box::from_raw(block));
+            }
+        }
+    }
+}
+
+impl<T> fmt::Debug for SegQueue<T> {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        f.pad("SegQueue { .. }")
+    }
+}
+
+impl<T> Default for SegQueue<T> {
+    fn default() -> SegQueue<T> {
+        SegQueue::new()
+    }
+}
+
+impl<T> IntoIterator for SegQueue<T> {
+    type Item = T;
+
+    type IntoIter = IntoIter<T>;
+
+    fn into_iter(self) -> Self::IntoIter {
+        IntoIter { value: self }
+    }
+}
+
+#[derive(Debug)]
+pub struct IntoIter<T> {
+    value: SegQueue<T>,
+}
+
+impl<T> Iterator for IntoIter<T> {
+    type Item = T;
+
+    fn next(&mut self) -> Option<Self::Item> {
+        let value = &mut self.value;
+        let head = *value.head.index.get_mut();
+        let tail = *value.tail.index.get_mut();
+        if head >> SHIFT == tail >> SHIFT {
+            None
+        } else {
+            let block = *value.head.block.get_mut();
+            let offset = (head >> SHIFT) % LAP;
+
+            // SAFETY: We have mutable access to this, so we can read without
+            // worrying about concurrency. Furthermore, we know this is
+            // initialized because it is the value pointed at by `value.head`
+            // and this is a non-empty queue.
+            let item = unsafe {
+                let slot = (*block).slots.get_unchecked(offset);
+                let p = &mut *slot.value.get();
+                p.as_mut_ptr().read()
+            };
+            if offset + 1 == BLOCK_CAP {
+                // Deallocate the block and move to the next one.
+                // SAFETY: The block is initialized because we've been reading
+                // from it this entire time. We can drop it b/c everything has
+                // been read out of it, so nothing is pointing to it anymore.
+                unsafe {
+                    let next = *(*block).next.get_mut();
+                    drop(Box::from_raw(block));
+                    *value.head.block.get_mut() = next;
+                }
+                // The last value in a block is empty, so skip it
+                *value.head.index.get_mut() = head.wrapping_add(2 << SHIFT);
+                // Double-check that we're pointing to the first item in a block.
+                debug_assert_eq!((*value.head.index.get_mut() >> SHIFT) % LAP, 0);
+            } else {
+                *value.head.index.get_mut() = head.wrapping_add(1 << SHIFT);
+            }
+            Some(item)
+        }
+    }
+}