Struct evmap::WriteHandle

pub struct WriteHandle<K, V, M = (), S = RandomState> where
    K: Eq + Hash + Clone,
    S: BuildHasher + Clone,
    V: Eq + Hash + ShallowCopy,
    M: 'static + Clone,  { /* fields omitted */ }

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 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));

Implementations

impl<K, V, M, S> WriteHandle<K, V, M, S> where
    K: Eq + Hash + Clone,
    S: BuildHasher + Clone,
    V: Eq + Hash + ShallowCopy,
    M: 'static + Clone, 

pub fn publish(&mut self) -> &mut Self

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 has_pending(&self) -> bool

Returns true if there are changes to the map that have not yet been exposed to readers.

pub fn set_meta(&mut self, meta: M)

Set the metadata.

Will only be visible to readers after the next call to publish.

pub fn insert(&mut self, k: K, v: V) -> &mut 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.

pub fn update(&mut self, k: K, v: V) -> &mut Self

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 for more information.

The new value will only be visible to readers after the next call to publish.

pub fn clear(&mut self, k: K) -> &mut Self

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.

pub fn remove(&mut self, k: K, v: V) -> &mut Self

👎 Deprecated since 11.0.0:

Renamed to remove_value

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.

pub fn remove_value(&mut self, k: K, v: V) -> &mut Self

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.

pub fn empty(&mut self, k: K) -> &mut Self

👎 Deprecated since 11.0.0:

Renamed to remove_entry

Remove the value-bag for the given key.

The value-bag will only disappear from readers after the next call to publish.

pub fn remove_entry(&mut self, k: K) -> &mut Self

Remove the value-bag for the given key.

The value-bag will only disappear from readers after the next call to publish.

pub fn purge(&mut self) -> &mut Self

Purge all value-bags from the map.

The map will only appear empty to readers after the next call to publish.

Note that this will iterate once over all the keys internally.

pub unsafe fn retain<F>(&mut self, k: K, f: F) -> &mut Self where
    F: FnMut(&V, bool) -> bool + 'static + Send, 

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

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 fn fit(&mut self, k: K) -> &mut Self

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

pub fn fit_all(&mut self) -> &mut Self

Like WriteHandle::fit, but shrinks all value-bags in the map.

The optimized value-bags will only be visible to readers after the next call to publish

pub fn reserve(&mut self, k: K, additional: usize) -> &mut Self

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.

Methods from Deref<Target = ReadHandle<K, V, M, S>>

pub fn enter(&self) -> Option<MapReadRef<'_, K, V, M, S>>

Take out a guarded live reference to the read side of the map.

This lets you perform more complex read operations on the map.

While the reference lives, changes to the map cannot be published.

If no publish has happened, or the map has been destroyed, this function returns None.

See MapReadRef.

pub fn len(&self) -> usize

Returns the number of non-empty keys present in the map.

pub fn is_empty(&self) -> bool

Returns true if the map contains no elements.

pub fn meta(&self) -> Option<ReadGuard<'_, M>>

Get the current meta value.

pub fn get<'rh, Q: ?Sized>(
    &'rh self,
    key: &Q
) -> Option<ReadGuard<'rh, Values<V, S>>> where
    K: Borrow<Q>,
    Q: Hash + Eq, 

Returns a guarded reference to the values corresponding to the key.

While the guard lives, changes to the map cannot be published.

The key may be any borrowed form of the map's key type, but Hash and Eq on the borrowed form must match those for the key type.

Note that not all writes will be included with this read -- only those that have been published by the writer. If no publish has happened, or the map has been destroyed, this function returns None.

pub fn get_one<'rh, Q: ?Sized>(&'rh self, key: &Q) -> Option<ReadGuard<'rh, V>> where
    K: Borrow<Q>,
    Q: Hash + Eq, 

Returns a guarded reference to one value corresponding to the key.

This is mostly intended for use when you are working with no more than one value per key. If there are multiple values stored for this key, there are no guarantees to which element is returned.

While the guard lives, changes to the map cannot be published.

The key may be any borrowed form of the map's key type, but Hash and Eq on the borrowed form must match those for the key type.

Note that not all writes will be included with this read -- only those that have been refreshed by the writer. If no refresh has happened, or the map has been destroyed, this function returns None.

pub fn meta_get<Q: ?Sized>(
    &self,
    key: &Q
) -> Option<(Option<ReadGuard<'_, Values<V, S>>>, M)> where
    K: Borrow<Q>,
    Q: Hash + Eq, 

Returns a guarded reference to the values corresponding to the key along with the map meta.

While the guard lives, changes to the map cannot be published.

The key may be any borrowed form of the map's key type, but Hash and Eq on the borrowed form must match those for the key type.

Note that not all writes will be included with this read -- only those that have been refreshed by the writer. If no refresh has happened, or the map has been destroyed, this function returns None.

If no values exist for the given key, Some(None, _) is returned.

pub fn was_dropped(&self) -> bool

Returns true if the WriteHandle has been dropped.

pub fn contains_key<Q: ?Sized>(&self, key: &Q) -> bool where
    K: Borrow<Q>,
    Q: Hash + Eq, 

Returns true if the map contains any values for the specified key.

The key may be any borrowed form of the map's key type, but Hash and Eq on the borrowed form must match those for the key type.

pub fn contains_value<Q: ?Sized, W: ?Sized>(&self, key: &Q, value: &W) -> bool where
    K: Borrow<Q>,
    V: Borrow<W>,
    Q: Hash + Eq,
    W: Hash + Eq, 

Returns true if the map contains the specified value for the specified key.

The key and value may be any borrowed form of the map's respective types, but Hash and Eq on the borrowed form must match.

pub fn map_into<Map, Collector, Target>(&self, f: Map) -> Collector where
    Map: FnMut(&K, &Values<V, S>) -> Target,
    Collector: FromIterator<Target>, 

Read all values in the map, and transform them into a new collection.

Trait Implementations

impl<K, V, M, S> Debug for WriteHandle<K, V, M, S> where
    K: Eq + Hash + Clone + Debug,
    S: BuildHasher + Clone,
    V: Eq + Hash + ShallowCopy + Debug,
    M: 'static + Clone + Debug, 

pub fn fmt(&self, f: &mut Formatter<'_>) -> Result

Formats the value using the given formatter.

impl<K, V, M, S> Deref for WriteHandle<K, V, M, S> where
    K: Eq + Hash + Clone,
    S: BuildHasher + Clone,
    V: Eq + Hash + ShallowCopy,
    M: 'static + Clone, 

type Target = ReadHandle<K, V, M, S>

The resulting type after dereferencing.

pub fn deref(&self) -> &Self::Target

Dereferences the value.

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 + ShallowCopy,
    M: 'static + Clone, 

pub fn extend<I: IntoIterator<Item = (K, V)>>(&mut self, iter: I)

Extends a collection with the contents of an iterator.

pub fn extend_one(&mut self, item: A)

🔬 This is a nightly-only experimental API. (extend_one)

Extends a collection with exactly one element.

pub fn extend_reserve(&mut self, additional: usize)

🔬 This is a nightly-only experimental API. (extend_one)

Reserves capacity in a collection for the given number of additional elements.