Struct WatermarkUpdate 

pub struct WatermarkUpdate<T>(/* private fields */);

Update from ranks for watermark accumulator using Last-Writer-Wins CRDT.

This is a proper CRDT that tracks the latest value from each rank using logical timestamps. When updates from the same rank are merged, the one with the higher timestamp wins. This allows ranks to report values that may decrease (e.g., during failure recovery) while maintaining proper commutativity and idempotence.

CRDT Properties

• Commutative: Merge order doesn’t matter (timestamps resolve conflicts)
• Idempotent: Merging duplicate updates has no effect
• Convergent: All replicas converge to the same state

Watermark Semantics

The watermark is the minimum value across all ranks’ latest reports. “Latest” is determined by logical timestamp, not arrival order.

Implementations

impl<T: Ord + Clone> WatermarkUpdate<T>

pub fn get(&self) -> &T

Get the watermark value (minimum of all ranks’ current values).

WatermarkUpdate is guaranteed to be initialized by the accumulator before it is sent to the user.

pub fn get_rank(&self, rank: Index) -> Option<&T>

Get the current value for a specific rank, if present.

pub fn num_ranks(&self) -> usize

Get the number of ranks currently tracked.

Trait Implementations

impl<T: Clone> Clone for WatermarkUpdate<T>

fn clone(&self) -> WatermarkUpdate<T>

Returns a duplicate of the value.

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

Performs copy-assignment from source.

impl<T: Debug> Debug for WatermarkUpdate<T>

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

Formats the value using the given formatter.

impl<T: Default> Default for WatermarkUpdate<T>

fn default() -> WatermarkUpdate<T>

Returns the “default value” for a type.

impl<'de, T> Deserialize<'de> for WatermarkUpdate<T>

where T: Deserialize<'de>,

fn deserialize<__D>(__deserializer: __D) -> Result<Self, __D::Error>

where __D: Deserializer<'de>,

Deserialize this value from the given Serde deserializer.

impl<T> From<(usize, T, u64)> for WatermarkUpdate<T>

fn from((rank, value, timestamp): (Index, T, u64)) -> Self

Create a watermark update from (rank, value, timestamp).

The timestamp should be a logical clock value (Lamport clock, sequence number, or monotonic counter) that increases with each update from the same rank.

impl<T: Clone + PartialEq> JoinSemilattice for WatermarkUpdate<T>

fn join(&self, other: &Self) -> Self

The join (least upper bound).

fn join_assign(&mut self, other: &Self)

In-place variant.

fn join_all<I>(it: I) -> Option<Self>

where I: IntoIterator<Item = Self>,

Join a finite iterator of values. Returns None for empty iterators.

impl<T: Named> Named for WatermarkUpdate<T>

fn typename() -> &'static str

The globally unique type name for the type. This should typically be the fully qualified Rust name of the type.

fn typehash() -> u64

A globally unique hash for this type. TODO: actually enforce perfect hashing

fn typeid() -> TypeId

The TypeId for this type. TypeIds are unique only within a binary, and should not be used for global identification.

fn port() -> u64

The globally unique port for this type. Typed ports are in the range of 1<<63..1<<64-1.

fn arm(&self) -> Option<&'static str>

If the named type is an enum, this returns the name of the arm of the value self.

unsafe fn arm_unchecked(self_: *const ()) -> Option<&'static str>

An unsafe version of ‘arm’, accepting a pointer to the value, for use in type-erased settings.

impl<T> Serialize for WatermarkUpdate<T>

where T: Serialize,

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

where __S: Serializer,

Serialize this value into the given Serde serializer.