Enum MergePolicy 

pub enum MergePolicy {
    KeyUnion,
    Exclusive,
    Cas,
    Accumulate,
}

How concurrent writers of one shared resource are reconciled.

There is deliberately no “last writer wins” variant: silently discarding a differing value is the behaviour this contract removes. Every accepted policy either refuses the conflict or was chosen in advance for it.

Variants

KeyUnion

Disjoint keys merge; a key already written by a different writer with different content is an explicit conflict. The default, because it is the only policy that accepts the common disjoint case without ever discarding a differing value.

Exclusive

The resource accepts writes from the one writer the plan names; any other writer is refused.

Cas

Every write is checked against the revision the writer read.

Accumulate

The resource holds a collection: a key already written is merged with the incoming value as a canonical set union of the two arrays.

This is the policy for a key whose declared meaning is “the set of contributions from the members of one node visit” — the results a workset’s items produce, for instance. It is the only merge of concurrent producers into one collection that is commutative, associative, idempotent and content preserving: completion order stays unobservable, a re-delivered contribution does not count twice, and no member’s value is dropped. Its members must therefore be independent by construction; two writers disagreeing about one value still belong to a scalar key, where KeyUnion refuses the disagreement.

Trait Implementations

impl Clone for MergePolicy

fn clone(&self) -> MergePolicy

Returns a duplicate of the value.

fn clone_from(&mut self, source: &Self)

Performs copy-assignment from source.

impl Copy for MergePolicy

impl Debug for MergePolicy

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

Formats the value using the given formatter.

impl Default for MergePolicy

fn default() -> MergePolicy

Returns the “default value” for a type.

impl<'de> Deserialize<'de> for MergePolicy

fn deserialize<__D>( __deserializer: __D, ) -> Result<MergePolicy, <__D as Deserializer<'de>>::Error>

where __D: Deserializer<'de>,

Deserialize this value from the given Serde deserializer.

impl Eq for MergePolicy

impl PartialEq for MergePolicy

fn eq(&self, other: &MergePolicy) -> bool

Equality operator ==.

fn ne(&self, other: &Rhs) -> bool

Inequality operator !=.

impl Serialize for MergePolicy

fn serialize<__S>( &self, __serializer: __S, ) -> Result<<__S as Serializer>::Ok, <__S as Serializer>::Error>

where __S: Serializer,

Serialize this value into the given Serde serializer.

impl StructuralPartialEq for MergePolicy