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use crate::inner::{Entry, Inner}; use crate::read::ReadHandle; use crate::values::ValuesInner; use left_right::{aliasing::Aliased, Absorb}; use std::collections::hash_map::RandomState; use std::fmt; use std::hash::{BuildHasher, Hash}; /// A handle that may be used to modify the eventually consistent map. /// /// Note that any changes made to the map will not be made visible to readers until /// [`publish`](Self::publish) is called. /// /// When the `WriteHandle` is dropped, the map is immediately (but safely) taken away from all /// readers, causing all future lookups to return `None`. /// /// # Examples /// ``` /// let x = ('x', 42); /// /// let (mut w, r) = evmap::new(); /// /// // the map is uninitialized, so all lookups should return None /// assert_eq!(r.get(&x.0).map(|rs| rs.len()), None); /// /// w.publish(); /// /// // after the first publish, it is empty, but ready /// assert_eq!(r.get(&x.0).map(|rs| rs.len()), None); /// /// w.insert(x.0, x); /// /// // it is empty even after an add (we haven't publish yet) /// assert_eq!(r.get(&x.0).map(|rs| rs.len()), None); /// /// w.publish(); /// /// // but after the swap, the record is there! /// assert_eq!(r.get(&x.0).map(|rs| rs.len()), Some(1)); /// assert_eq!(r.get(&x.0).map(|rs| rs.iter().any(|v| v.0 == x.0 && v.1 == x.1)), Some(true)); /// ``` pub struct WriteHandle<K, V, M = (), S = RandomState> where K: Eq + Hash + Clone, S: BuildHasher + Clone, V: Eq + Hash, M: 'static + Clone, { handle: left_right::WriteHandle<Inner<K, V, M, S>, Operation<K, V, M>>, r_handle: ReadHandle<K, V, M, S>, } impl<K, V, M, S> fmt::Debug for WriteHandle<K, V, M, S> where K: Eq + Hash + Clone + fmt::Debug, S: BuildHasher + Clone, V: Eq + Hash + fmt::Debug, M: 'static + Clone + fmt::Debug, { fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result { f.debug_struct("WriteHandle") .field("handle", &self.handle) .finish() } } impl<K, V, M, S> WriteHandle<K, V, M, S> where K: Eq + Hash + Clone, S: BuildHasher + Clone, V: Eq + Hash, M: 'static + Clone, { pub(crate) fn new( handle: left_right::WriteHandle<Inner<K, V, M, S>, Operation<K, V, M>>, ) -> Self { let r_handle = ReadHandle::new(left_right::ReadHandle::clone(&*handle)); Self { handle, r_handle } } /// Publish all changes since the last call to `publish` to make them visible to readers. /// /// This can take some time, especially if readers are executing slow operations, or if there /// are many of them. pub fn publish(&mut self) -> &mut Self { self.handle.publish(); self } /// Returns true if there are changes to the map that have not yet been exposed to readers. pub fn has_pending(&self) -> bool { self.handle.has_pending_operations() } /// Set the metadata. /// /// Will only be visible to readers after the next call to [`publish`](Self::publish). pub fn set_meta(&mut self, meta: M) { self.add_op(Operation::SetMeta(meta)); } fn add_op(&mut self, op: Operation<K, V, M>) -> &mut Self { self.handle.append(op); self } /// Add the given value to the value-bag of the given key. /// /// The updated value-bag will only be visible to readers after the next call to /// [`publish`](Self::publish). pub fn insert(&mut self, k: K, v: V) -> &mut Self { self.add_op(Operation::Add(k, Aliased::from(v))) } /// Replace the value-bag of the given key with the given value. /// /// Replacing the value will automatically deallocate any heap storage and place the new value /// back into the `SmallVec` inline storage. This can improve cache locality for common /// cases where the value-bag is only ever a single element. /// /// See [the doc section on this](./index.html#small-vector-optimization) for more information. /// /// The new value will only be visible to readers after the next call to /// [`publish`](Self::publish). pub fn update(&mut self, k: K, v: V) -> &mut Self { self.add_op(Operation::Replace(k, Aliased::from(v))) } /// Clear the value-bag of the given key, without removing it. /// /// If a value-bag already exists, this will clear it but leave the /// allocated memory intact for reuse, or if no associated value-bag exists /// an empty value-bag will be created for the given key. /// /// The new value will only be visible to readers after the next call to /// [`publish`](Self::publish). pub fn clear(&mut self, k: K) -> &mut Self { self.add_op(Operation::Clear(k)) } /// Remove the given value from the value-bag of the given key. /// /// The updated value-bag will only be visible to readers after the next call to /// [`publish`](Self::publish). #[deprecated(since = "11.0.0", note = "Renamed to remove_value")] pub fn remove(&mut self, k: K, v: V) -> &mut Self { self.remove_value(k, v) } /// Remove the given value from the value-bag of the given key. /// /// The updated value-bag will only be visible to readers after the next call to /// [`publish`](Self::publish). pub fn remove_value(&mut self, k: K, v: V) -> &mut Self { self.add_op(Operation::RemoveValue(k, v)) } /// Remove the value-bag for the given key. /// /// The value-bag will only disappear from readers after the next call to /// [`publish`](Self::publish). #[deprecated(since = "11.0.0", note = "Renamed to remove_entry")] pub fn empty(&mut self, k: K) -> &mut Self { self.remove_entry(k) } /// Remove the value-bag for the given key. /// /// The value-bag will only disappear from readers after the next call to /// [`publish`](Self::publish). pub fn remove_entry(&mut self, k: K) -> &mut Self { self.add_op(Operation::RemoveEntry(k)) } /// Purge all value-bags from the map. /// /// The map will only appear empty to readers after the next call to /// [`publish`](Self::publish). /// /// Note that this will iterate once over all the keys internally. pub fn purge(&mut self) -> &mut Self { self.add_op(Operation::Purge) } /// Retain elements for the given key using the provided predicate function. /// /// The remaining value-bag will only be visible to readers after the next call to /// [`publish`](Self::publish) /// /// # Safety /// /// The given closure is called _twice_ for each element, once when called, and once /// on swap. It _must_ retain the same elements each time, otherwise a value may exist in one /// map, but not the other, leaving the two maps permanently out-of-sync. This is _really_ bad, /// as values are aliased between the maps, and are assumed safe to free when they leave the /// map during a `publish`. Returning `true` when `retain` is first called for a value, and /// `false` the second time would free the value, but leave an aliased pointer to it in the /// other side of the map. /// /// The arguments to the predicate function are the current value in the value-bag, and `true` /// if this is the first value in the value-bag on the second map, or `false` otherwise. Use /// the second argument to know when to reset any closure-local state to ensure deterministic /// operation. /// /// So, stated plainly, the given closure _must_ return the same order of true/false for each /// of the two iterations over the value-bag. That is, the sequence of returned booleans before /// the second argument is true must be exactly equal to the sequence of returned booleans /// at and beyond when the second argument is true. pub unsafe fn retain<F>(&mut self, k: K, f: F) -> &mut Self where F: FnMut(&V, bool) -> bool + 'static + Send, { self.add_op(Operation::Retain(k, Predicate(Box::new(f)))) } /// Shrinks a value-bag to it's minimum necessary size, freeing memory /// and potentially improving cache locality by switching to inline storage. /// /// The optimized value-bag will only be visible to readers after the next call to /// [`publish`](Self::publish) pub fn fit(&mut self, k: K) -> &mut Self { self.add_op(Operation::Fit(Some(k))) } /// Like [`WriteHandle::fit`](#method.fit), but shrinks <b>all</b> value-bags in the map. /// /// The optimized value-bags will only be visible to readers after the next call to /// [`publish`](Self::publish) pub fn fit_all(&mut self) -> &mut Self { self.add_op(Operation::Fit(None)) } /// Reserves capacity for some number of additional elements in a value-bag, /// or creates an empty value-bag for this key with the given capacity if /// it doesn't already exist. /// /// Readers are unaffected by this operation, but it can improve performance /// by pre-allocating space for large value-bags. pub fn reserve(&mut self, k: K, additional: usize) -> &mut Self { self.add_op(Operation::Reserve(k, additional)) } #[cfg(feature = "eviction")] /// Remove the value-bag for `n` randomly chosen keys. /// /// This method immediately calls [`publish`](Self::publish) to ensure that the keys and values /// it returns match the elements that will be emptied on the next call to /// [`publish`](Self::publish). The value-bags will only disappear from readers after the next /// call to [`publish`](Self::publish). pub fn empty_random<'a>( &'a mut self, rng: &mut impl rand::Rng, n: usize, ) -> impl ExactSizeIterator<Item = (&'a K, &'a crate::values::Values<V, S>)> { // force a publish so that our view into self.r_handle matches the indices we choose. // if we didn't do this, the `i`th element of r_handle may be a completely different // element than the one that _will_ be evicted when `EmptyAt([.. i ..])` is applied. // this would be bad since we are telling the caller which elements we are evicting! // note also that we _must_ use `r_handle`, not `w_handle`, since `w_handle` may have // pending operations even after a publish! self.publish(); let inner = self .r_handle .handle .raw_handle() .expect("WriteHandle has not been dropped"); // safety: the writer cannot publish until 'a ends, so we know that reading from the read // map is safe for the duration of 'a. let inner: &'a Inner<K, V, M, S> = unsafe { std::mem::transmute::<&Inner<K, V, M, S>, _>(inner.as_ref()) }; let inner = &inner.data; // let's pick some (distinct) indices to evict! let n = n.min(inner.len()); let indices = rand::seq::index::sample(rng, inner.len(), n); // we need to sort the indices so that, later, we can make sure to swap remove from last to // first (and so not accidentally remove the wrong index). let mut to_remove = indices.clone().into_vec(); to_remove.sort(); self.add_op(Operation::EmptyAt(to_remove)); indices.into_iter().map(move |i| { let (k, vs) = inner.get_index(i).expect("in-range"); (k, vs.as_ref()) }) } } impl<K, V, M, S> Absorb<Operation<K, V, M>> for Inner<K, V, M, S> where K: Eq + Hash + Clone, S: BuildHasher + Clone, V: Eq + Hash, M: 'static + Clone, { /// Apply ops in such a way that no values are dropped, only forgotten fn absorb_first(&mut self, op: &mut Operation<K, V, M>, other: &Self) { // Safety note for calls to .alias(): // // it is safe to alias this value here because if it is ever removed, one alias is always // first dropped with NoDrop (in absorb_first), and _then_ the other (and only remaining) // alias is dropped with DoDrop (in absorb_second). we won't drop the aliased value until // _after_ absorb_second is called on this operation, so leaving an alias in the oplog is // also safe. let hasher = other.data.hasher(); match *op { Operation::Replace(ref key, ref mut value) => { let vs = self .data .entry(key.clone()) .or_insert_with(ValuesInner::new); // truncate vector vs.clear(); // implicit shrink_to_fit on replace op // so it will switch back to inline allocation for the subsequent push. vs.shrink_to_fit(); vs.push(unsafe { value.alias() }, hasher); } Operation::Clear(ref key) => { self.data .entry(key.clone()) .or_insert_with(ValuesInner::new) .clear(); } Operation::Add(ref key, ref mut value) => { self.data .entry(key.clone()) .or_insert_with(ValuesInner::new) .push(unsafe { value.alias() }, hasher); } Operation::RemoveEntry(ref key) => { #[cfg(not(feature = "indexed"))] self.data.remove(key); #[cfg(feature = "indexed")] self.data.swap_remove(key); } Operation::Purge => { self.data.clear(); } #[cfg(feature = "eviction")] Operation::EmptyAt(ref indices) => { for &index in indices.iter().rev() { self.data.swap_remove_index(index); } } Operation::RemoveValue(ref key, ref value) => { if let Some(e) = self.data.get_mut(key) { e.swap_remove(&value); } } Operation::Retain(ref key, ref mut predicate) => { if let Some(e) = self.data.get_mut(key) { let mut first = true; e.retain(move |v| { let retain = predicate.eval(v, first); first = false; retain }); } } Operation::Fit(ref key) => match key { Some(ref key) => { if let Some(e) = self.data.get_mut(key) { e.shrink_to_fit(); } } None => { for value_set in self.data.values_mut() { value_set.shrink_to_fit(); } } }, Operation::Reserve(ref key, additional) => match self.data.entry(key.clone()) { Entry::Occupied(mut entry) => { entry.get_mut().reserve(additional, hasher); } Entry::Vacant(entry) => { entry.insert(ValuesInner::with_capacity_and_hasher(additional, hasher)); } }, Operation::MarkReady => { self.ready = true; } Operation::SetMeta(ref m) => { self.meta = m.clone(); } } } /// Apply operations while allowing dropping of values fn absorb_second(&mut self, op: Operation<K, V, M>, other: &Self) { // # Safety (for cast): // // See the module-level documentation for left_right::aliasing. // NoDrop and DoDrop are both private, therefore this cast is (likely) sound. // // # Safety (for NoDrop -> DoDrop): // // It is safe for us to drop values the second time each operation has been // performed, since if they are dropped here, they were also dropped in the first // application of the operation, which removed the only other alias. // // FIXME: This is where the non-determinism of Hash and PartialEq hits us (#78). let inner: &mut Inner<K, V, M, S, crate::aliasing::DoDrop> = unsafe { &mut *(self as *mut _ as *mut _) }; // Safety note for calls to .change_drop(): // // we're turning a NoDrop into DoDrop, so we must be prepared for a drop. // if absorb_first dropped its alias, then `value` is the only alias // if absorb_first did not drop its alias, then `value` will not be dropped here either, // and at the end of scope we revert to `NoDrop`, so all is well. let hasher = other.data.hasher(); match op { Operation::Replace(key, value) => { let v = inner.data.entry(key).or_insert_with(ValuesInner::new); v.clear(); v.shrink_to_fit(); v.push(unsafe { value.change_drop() }, hasher); } Operation::Clear(key) => { inner .data .entry(key) .or_insert_with(ValuesInner::new) .clear(); } Operation::Add(key, value) => { // safety (below): // we're turning a NoDrop into DoDrop, so we must be prepared for a drop. // if absorb_first dropped the value, then `value` is the only alias // if absorb_first did not drop the value, then `value` will not be dropped here // either, and at the end of scope we revert to `NoDrop`, so all is well. inner .data .entry(key) .or_insert_with(ValuesInner::new) .push(unsafe { value.change_drop() }, hasher); } Operation::RemoveEntry(key) => { #[cfg(not(feature = "indexed"))] inner.data.remove(&key); #[cfg(feature = "indexed")] inner.data.swap_remove(&key); } Operation::Purge => { inner.data.clear(); } #[cfg(feature = "eviction")] Operation::EmptyAt(indices) => { for &index in indices.iter().rev() { inner.data.swap_remove_index(index); } } Operation::RemoveValue(key, value) => { if let Some(e) = inner.data.get_mut(&key) { // find the first entry that matches all fields e.swap_remove(&value); } } Operation::Retain(key, mut predicate) => { if let Some(e) = inner.data.get_mut(&key) { let mut first = true; e.retain(move |v| { let retain = predicate.eval(&*v, first); first = false; retain }); } } Operation::Fit(key) => match key { Some(ref key) => { if let Some(e) = inner.data.get_mut(key) { e.shrink_to_fit(); } } None => { for value_set in inner.data.values_mut() { value_set.shrink_to_fit(); } } }, Operation::Reserve(key, additional) => match inner.data.entry(key) { Entry::Occupied(mut entry) => { entry.get_mut().reserve(additional, hasher); } Entry::Vacant(entry) => { entry.insert(ValuesInner::with_capacity_and_hasher(additional, hasher)); } }, Operation::MarkReady => { inner.ready = true; } Operation::SetMeta(m) => { inner.meta = m; } } } fn drop_first(self: Box<Self>) { // since the two copies are exactly equal, we need to make sure that we *don't* call the // destructors of any of the values that are in our map, as they'll all be called when the // last read handle goes out of scope. that's easy enough since none of them will be // dropped by default. } fn drop_second(self: Box<Self>) { // when the second copy is dropped is where we want to _actually_ drop all the values in // the map. we do this by setting the generic type to the one that causes drops to happen. // // safety: since we're going second, we know that all the aliases in the first map have // gone away, so all of our aliases must be the only ones. let inner: Box<Inner<K, V, M, S, crate::aliasing::DoDrop>> = unsafe { Box::from_raw(Box::into_raw(self) as *mut _ as *mut _) }; drop(inner); } fn sync_with(&mut self, first: &Self) { let inner: &mut Inner<K, V, M, S, crate::aliasing::DoDrop> = unsafe { &mut *(self as *mut _ as *mut _) }; inner.data.extend(first.data.iter().map(|(k, vs)| { // # Safety (for aliasing): // // We are aliasing every value in the read map, and the oplog has no other // pending operations (by the semantics of JustCloneRHandle). For any of the // values we alias to be dropped, the operation that drops it must first be // enqueued to the oplog, at which point it will _first_ go through // absorb_first, which will remove the alias and leave only one alias left. // Only after that, when that operation eventually goes through absorb_second, // will the alias be dropped, and by that time it is the only value. // // # Safety (for hashing): // // Due to `RandomState` there can be subtle differences between the iteration order // of two `HashMap` instances. We prevent this by using `left_right::new_with_empty`, // which `clone`s the first map, making them use the same hasher. // // # Safety (for NoDrop -> DoDrop): // // The oplog has only this one operation in it for the first call to `publish`, // so we are about to turn the alias back into NoDrop. (k.clone(), unsafe { ValuesInner::alias(vs, first.data.hasher()) }) })); self.ready = true; } } impl<K, V, M, S> Extend<(K, V)> for WriteHandle<K, V, M, S> where K: Eq + Hash + Clone, S: BuildHasher + Clone, V: Eq + Hash, M: 'static + Clone, { fn extend<I: IntoIterator<Item = (K, V)>>(&mut self, iter: I) { for (k, v) in iter { self.insert(k, v); } } } // allow using write handle for reads use std::ops::Deref; impl<K, V, M, S> Deref for WriteHandle<K, V, M, S> where K: Eq + Hash + Clone, S: BuildHasher + Clone, V: Eq + Hash, M: 'static + Clone, { type Target = ReadHandle<K, V, M, S>; fn deref(&self) -> &Self::Target { &self.r_handle } } /// A pending map operation. #[non_exhaustive] pub(super) enum Operation<K, V, M> { /// Replace the set of entries for this key with this value. Replace(K, Aliased<V, crate::aliasing::NoDrop>), /// Add this value to the set of entries for this key. Add(K, Aliased<V, crate::aliasing::NoDrop>), /// Remove this value from the set of entries for this key. RemoveValue(K, V), /// Remove the value set for this key. RemoveEntry(K), #[cfg(feature = "eviction")] /// Drop keys at the given indices. /// /// The list of indices must be sorted in ascending order. EmptyAt(Vec<usize>), /// Remove all values in the value set for this key. Clear(K), /// Remove all values for all keys. /// /// Note that this will iterate once over all the keys internally. Purge, /// Retains all values matching the given predicate. Retain(K, Predicate<V>), /// Shrinks [`Values`] to their minimum necessary size, freeing memory /// and potentially improving cache locality. /// /// If no key is given, all `Values` will shrink to fit. Fit(Option<K>), /// Reserves capacity for some number of additional elements in [`Values`] /// for the given key. If the given key does not exist, allocate an empty /// `Values` with the given capacity. /// /// This can improve performance by pre-allocating space for large bags of values. Reserve(K, usize), /// Mark the map as ready to be consumed for readers. MarkReady, /// Set the value of the map meta. SetMeta(M), } impl<K, V, M> fmt::Debug for Operation<K, V, M> where K: fmt::Debug, V: fmt::Debug, M: fmt::Debug, { fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result { match *self { Operation::Replace(ref a, ref b) => f.debug_tuple("Replace").field(a).field(b).finish(), Operation::Add(ref a, ref b) => f.debug_tuple("Add").field(a).field(b).finish(), Operation::RemoveValue(ref a, ref b) => { f.debug_tuple("RemoveValue").field(a).field(b).finish() } Operation::RemoveEntry(ref a) => f.debug_tuple("RemoveEntry").field(a).finish(), #[cfg(feature = "eviction")] Operation::EmptyAt(ref a) => f.debug_tuple("EmptyAt").field(a).finish(), Operation::Clear(ref a) => f.debug_tuple("Clear").field(a).finish(), Operation::Purge => f.debug_tuple("Purge").finish(), Operation::Retain(ref a, ref b) => f.debug_tuple("Retain").field(a).field(b).finish(), Operation::Fit(ref a) => f.debug_tuple("Fit").field(a).finish(), Operation::Reserve(ref a, ref b) => f.debug_tuple("Reserve").field(a).field(b).finish(), Operation::MarkReady => f.debug_tuple("MarkReady").finish(), Operation::SetMeta(ref a) => f.debug_tuple("SetMeta").field(a).finish(), } } } /// Unary predicate used to retain elements. /// /// The predicate function is called once for each distinct value, and `true` if this is the /// _first_ call to the predicate on the _second_ application of the operation. pub(super) struct Predicate<V: ?Sized>(Box<dyn FnMut(&V, bool) -> bool + Send>); impl<V: ?Sized> Predicate<V> { /// Evaluate the predicate for the given element #[inline] fn eval(&mut self, value: &V, reset: bool) -> bool { (*self.0)(value, reset) } } impl<V: ?Sized> PartialEq for Predicate<V> { #[inline] fn eq(&self, other: &Self) -> bool { // only compare data, not vtable: https://stackoverflow.com/q/47489449/472927 &*self.0 as *const _ as *const () == &*other.0 as *const _ as *const () } } impl<V: ?Sized> Eq for Predicate<V> {} impl<V: ?Sized> fmt::Debug for Predicate<V> { fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result { f.debug_tuple("Predicate") .field(&format_args!("{:p}", &*self.0 as *const _)) .finish() } }