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Diffstat (limited to 'vendor/crossbeam-epoch/src/sync/list.rs')
| -rw-r--r-- | vendor/crossbeam-epoch/src/sync/list.rs | 487 |
1 files changed, 0 insertions, 487 deletions
diff --git a/vendor/crossbeam-epoch/src/sync/list.rs b/vendor/crossbeam-epoch/src/sync/list.rs deleted file mode 100644 index 52ffd6f..0000000 --- a/vendor/crossbeam-epoch/src/sync/list.rs +++ /dev/null @@ -1,487 +0,0 @@ -//! Lock-free intrusive linked list. -//! -//! Ideas from Michael. High Performance Dynamic Lock-Free Hash Tables and List-Based Sets. SPAA -//! 2002. <http://dl.acm.org/citation.cfm?id=564870.564881> - -use core::marker::PhantomData; -use core::sync::atomic::Ordering::{Acquire, Relaxed, Release}; - -use crate::{unprotected, Atomic, Guard, Shared}; - -/// An entry in a linked list. -/// -/// An Entry is accessed from multiple threads, so it would be beneficial to put it in a different -/// cache-line than thread-local data in terms of performance. -#[derive(Debug)] -pub(crate) struct Entry { - /// The next entry in the linked list. - /// If the tag is 1, this entry is marked as deleted. - next: Atomic<Entry>, -} - -/// Implementing this trait asserts that the type `T` can be used as an element in the intrusive -/// linked list defined in this module. `T` has to contain (or otherwise be linked to) an instance -/// of `Entry`. -/// -/// # Example -/// -/// ```ignore -/// struct A { -/// entry: Entry, -/// data: usize, -/// } -/// -/// impl IsElement<A> for A { -/// fn entry_of(a: &A) -> &Entry { -/// let entry_ptr = ((a as usize) + offset_of!(A, entry)) as *const Entry; -/// unsafe { &*entry_ptr } -/// } -/// -/// unsafe fn element_of(entry: &Entry) -> &T { -/// let elem_ptr = ((entry as usize) - offset_of!(A, entry)) as *const T; -/// &*elem_ptr -/// } -/// -/// unsafe fn finalize(entry: &Entry, guard: &Guard) { -/// guard.defer_destroy(Shared::from(Self::element_of(entry) as *const _)); -/// } -/// } -/// ``` -/// -/// This trait is implemented on a type separate from `T` (although it can be just `T`), because -/// one type might be placeable into multiple lists, in which case it would require multiple -/// implementations of `IsElement`. In such cases, each struct implementing `IsElement<T>` -/// represents a distinct `Entry` in `T`. -/// -/// For example, we can insert the following struct into two lists using `entry1` for one -/// and `entry2` for the other: -/// -/// ```ignore -/// struct B { -/// entry1: Entry, -/// entry2: Entry, -/// data: usize, -/// } -/// ``` -/// -pub(crate) trait IsElement<T> { - /// Returns a reference to this element's `Entry`. - fn entry_of(_: &T) -> &Entry; - - /// Given a reference to an element's entry, returns that element. - /// - /// ```ignore - /// let elem = ListElement::new(); - /// assert_eq!(elem.entry_of(), - /// unsafe { ListElement::element_of(elem.entry_of()) } ); - /// ``` - /// - /// # Safety - /// - /// The caller has to guarantee that the `Entry` is called with was retrieved from an instance - /// of the element type (`T`). - unsafe fn element_of(_: &Entry) -> &T; - - /// The function that is called when an entry is unlinked from list. - /// - /// # Safety - /// - /// The caller has to guarantee that the `Entry` is called with was retrieved from an instance - /// of the element type (`T`). - unsafe fn finalize(_: &Entry, _: &Guard); -} - -/// A lock-free, intrusive linked list of type `T`. -#[derive(Debug)] -pub(crate) struct List<T, C: IsElement<T> = T> { - /// The head of the linked list. - head: Atomic<Entry>, - - /// The phantom data for using `T` and `C`. - _marker: PhantomData<(T, C)>, -} - -/// An iterator used for retrieving values from the list. -pub(crate) struct Iter<'g, T, C: IsElement<T>> { - /// The guard that protects the iteration. - guard: &'g Guard, - - /// Pointer from the predecessor to the current entry. - pred: &'g Atomic<Entry>, - - /// The current entry. - curr: Shared<'g, Entry>, - - /// The list head, needed for restarting iteration. - head: &'g Atomic<Entry>, - - /// Logically, we store a borrow of an instance of `T` and - /// use the type information from `C`. - _marker: PhantomData<(&'g T, C)>, -} - -/// An error that occurs during iteration over the list. -#[derive(PartialEq, Debug)] -pub(crate) enum IterError { - /// A concurrent thread modified the state of the list at the same place that this iterator - /// was inspecting. Subsequent iteration will restart from the beginning of the list. - Stalled, -} - -impl Default for Entry { - /// Returns the empty entry. - fn default() -> Self { - Self { - next: Atomic::null(), - } - } -} - -impl Entry { - /// Marks this entry as deleted, deferring the actual deallocation to a later iteration. - /// - /// # Safety - /// - /// The entry should be a member of a linked list, and it should not have been deleted. - /// It should be safe to call `C::finalize` on the entry after the `guard` is dropped, where `C` - /// is the associated helper for the linked list. - pub(crate) unsafe fn delete(&self, guard: &Guard) { - self.next.fetch_or(1, Release, guard); - } -} - -impl<T, C: IsElement<T>> List<T, C> { - /// Returns a new, empty linked list. - pub(crate) fn new() -> Self { - Self { - head: Atomic::null(), - _marker: PhantomData, - } - } - - /// Inserts `entry` into the head of the list. - /// - /// # Safety - /// - /// You should guarantee that: - /// - /// - `container` is not null - /// - `container` is immovable, e.g. inside an `Owned` - /// - the same `Entry` is not inserted more than once - /// - the inserted object will be removed before the list is dropped - pub(crate) unsafe fn insert<'g>(&'g self, container: Shared<'g, T>, guard: &'g Guard) { - // Insert right after head, i.e. at the beginning of the list. - let to = &self.head; - // Get the intrusively stored Entry of the new element to insert. - let entry: &Entry = C::entry_of(container.deref()); - // Make a Shared ptr to that Entry. - let entry_ptr = Shared::from(entry as *const _); - // Read the current successor of where we want to insert. - let mut next = to.load(Relaxed, guard); - - loop { - // Set the Entry of the to-be-inserted element to point to the previous successor of - // `to`. - entry.next.store(next, Relaxed); - match to.compare_exchange_weak(next, entry_ptr, Release, Relaxed, guard) { - Ok(_) => break, - // We lost the race or weak CAS failed spuriously. Update the successor and try - // again. - Err(err) => next = err.current, - } - } - } - - /// Returns an iterator over all objects. - /// - /// # Caveat - /// - /// Every object that is inserted at the moment this function is called and persists at least - /// until the end of iteration will be returned. Since this iterator traverses a lock-free - /// linked list that may be concurrently modified, some additional caveats apply: - /// - /// 1. If a new object is inserted during iteration, it may or may not be returned. - /// 2. If an object is deleted during iteration, it may or may not be returned. - /// 3. The iteration may be aborted when it lost in a race condition. In this case, the winning - /// thread will continue to iterate over the same list. - pub(crate) fn iter<'g>(&'g self, guard: &'g Guard) -> Iter<'g, T, C> { - Iter { - guard, - pred: &self.head, - curr: self.head.load(Acquire, guard), - head: &self.head, - _marker: PhantomData, - } - } -} - -impl<T, C: IsElement<T>> Drop for List<T, C> { - fn drop(&mut self) { - unsafe { - let guard = unprotected(); - let mut curr = self.head.load(Relaxed, guard); - while let Some(c) = curr.as_ref() { - let succ = c.next.load(Relaxed, guard); - // Verify that all elements have been removed from the list. - assert_eq!(succ.tag(), 1); - - C::finalize(curr.deref(), guard); - curr = succ; - } - } - } -} - -impl<'g, T: 'g, C: IsElement<T>> Iterator for Iter<'g, T, C> { - type Item = Result<&'g T, IterError>; - - fn next(&mut self) -> Option<Self::Item> { - while let Some(c) = unsafe { self.curr.as_ref() } { - let succ = c.next.load(Acquire, self.guard); - - if succ.tag() == 1 { - // This entry was removed. Try unlinking it from the list. - let succ = succ.with_tag(0); - - // The tag should always be zero, because removing a node after a logically deleted - // node leaves the list in an invalid state. - debug_assert!(self.curr.tag() == 0); - - // Try to unlink `curr` from the list, and get the new value of `self.pred`. - let succ = match self - .pred - .compare_exchange(self.curr, succ, Acquire, Acquire, self.guard) - { - Ok(_) => { - // We succeeded in unlinking `curr`, so we have to schedule - // deallocation. Deferred drop is okay, because `list.delete()` can only be - // called if `T: 'static`. - unsafe { - C::finalize(self.curr.deref(), self.guard); - } - - // `succ` is the new value of `self.pred`. - succ - } - Err(e) => { - // `e.current` is the current value of `self.pred`. - e.current - } - }; - - // If the predecessor node is already marked as deleted, we need to restart from - // `head`. - if succ.tag() != 0 { - self.pred = self.head; - self.curr = self.head.load(Acquire, self.guard); - - return Some(Err(IterError::Stalled)); - } - - // Move over the removed by only advancing `curr`, not `pred`. - self.curr = succ; - continue; - } - - // Move one step forward. - self.pred = &c.next; - self.curr = succ; - - return Some(Ok(unsafe { C::element_of(c) })); - } - - // We reached the end of the list. - None - } -} - -#[cfg(all(test, not(crossbeam_loom)))] -mod tests { - use super::*; - use crate::{Collector, Owned}; - use crossbeam_utils::thread; - use std::sync::Barrier; - - impl IsElement<Entry> for Entry { - fn entry_of(entry: &Entry) -> &Entry { - entry - } - - unsafe fn element_of(entry: &Entry) -> &Entry { - entry - } - - unsafe fn finalize(entry: &Entry, guard: &Guard) { - guard.defer_destroy(Shared::from(Self::element_of(entry) as *const _)); - } - } - - /// Checks whether the list retains inserted elements - /// and returns them in the correct order. - #[test] - fn insert() { - let collector = Collector::new(); - let handle = collector.register(); - let guard = handle.pin(); - - let l: List<Entry> = List::new(); - - let e1 = Owned::new(Entry::default()).into_shared(&guard); - let e2 = Owned::new(Entry::default()).into_shared(&guard); - let e3 = Owned::new(Entry::default()).into_shared(&guard); - - unsafe { - l.insert(e1, &guard); - l.insert(e2, &guard); - l.insert(e3, &guard); - } - - let mut iter = l.iter(&guard); - let maybe_e3 = iter.next(); - assert!(maybe_e3.is_some()); - assert!(maybe_e3.unwrap().unwrap() as *const Entry == e3.as_raw()); - let maybe_e2 = iter.next(); - assert!(maybe_e2.is_some()); - assert!(maybe_e2.unwrap().unwrap() as *const Entry == e2.as_raw()); - let maybe_e1 = iter.next(); - assert!(maybe_e1.is_some()); - assert!(maybe_e1.unwrap().unwrap() as *const Entry == e1.as_raw()); - assert!(iter.next().is_none()); - - unsafe { - e1.as_ref().unwrap().delete(&guard); - e2.as_ref().unwrap().delete(&guard); - e3.as_ref().unwrap().delete(&guard); - } - } - - /// Checks whether elements can be removed from the list and whether - /// the correct elements are removed. - #[test] - fn delete() { - let collector = Collector::new(); - let handle = collector.register(); - let guard = handle.pin(); - - let l: List<Entry> = List::new(); - - let e1 = Owned::new(Entry::default()).into_shared(&guard); - let e2 = Owned::new(Entry::default()).into_shared(&guard); - let e3 = Owned::new(Entry::default()).into_shared(&guard); - unsafe { - l.insert(e1, &guard); - l.insert(e2, &guard); - l.insert(e3, &guard); - e2.as_ref().unwrap().delete(&guard); - } - - let mut iter = l.iter(&guard); - let maybe_e3 = iter.next(); - assert!(maybe_e3.is_some()); - assert!(maybe_e3.unwrap().unwrap() as *const Entry == e3.as_raw()); - let maybe_e1 = iter.next(); - assert!(maybe_e1.is_some()); - assert!(maybe_e1.unwrap().unwrap() as *const Entry == e1.as_raw()); - assert!(iter.next().is_none()); - - unsafe { - e1.as_ref().unwrap().delete(&guard); - e3.as_ref().unwrap().delete(&guard); - } - - let mut iter = l.iter(&guard); - assert!(iter.next().is_none()); - } - - const THREADS: usize = 8; - const ITERS: usize = 512; - - /// Contends the list on insert and delete operations to make sure they can run concurrently. - #[test] - fn insert_delete_multi() { - let collector = Collector::new(); - - let l: List<Entry> = List::new(); - let b = Barrier::new(THREADS); - - thread::scope(|s| { - for _ in 0..THREADS { - s.spawn(|_| { - b.wait(); - - let handle = collector.register(); - let guard: Guard = handle.pin(); - let mut v = Vec::with_capacity(ITERS); - - for _ in 0..ITERS { - let e = Owned::new(Entry::default()).into_shared(&guard); - v.push(e); - unsafe { - l.insert(e, &guard); - } - } - - for e in v { - unsafe { - e.as_ref().unwrap().delete(&guard); - } - } - }); - } - }) - .unwrap(); - - let handle = collector.register(); - let guard = handle.pin(); - - let mut iter = l.iter(&guard); - assert!(iter.next().is_none()); - } - - /// Contends the list on iteration to make sure that it can be iterated over concurrently. - #[test] - fn iter_multi() { - let collector = Collector::new(); - - let l: List<Entry> = List::new(); - let b = Barrier::new(THREADS); - - thread::scope(|s| { - for _ in 0..THREADS { - s.spawn(|_| { - b.wait(); - - let handle = collector.register(); - let guard: Guard = handle.pin(); - let mut v = Vec::with_capacity(ITERS); - - for _ in 0..ITERS { - let e = Owned::new(Entry::default()).into_shared(&guard); - v.push(e); - unsafe { - l.insert(e, &guard); - } - } - - let mut iter = l.iter(&guard); - for _ in 0..ITERS { - assert!(iter.next().is_some()); - } - - for e in v { - unsafe { - e.as_ref().unwrap().delete(&guard); - } - } - }); - } - }) - .unwrap(); - - let handle = collector.register(); - let guard = handle.pin(); - - let mut iter = l.iter(&guard); - assert!(iter.next().is_none()); - } -} |