Struct SwimState 

pub struct SwimState { /* private fields */ }

The pure SWIM + Lifeguard state machine for one node.

Deterministic and I/O-free: every method takes a logical tick or an explicit event and returns the peer-state transitions to apply. See the module docs for the protocol and the two-layer rationale.

Implementations

impl SwimState

pub fn new(me: usize, n: usize, cfg: SwimConfig) -> Self

Build a state machine for node me in a group of n members. Every other member starts Status::Alive at incarnation 0 (the join-time optimistic assumption; a genuinely dead member is discovered by the first failed probe).

Panics

Panics if me >= n; a node must be a member of its own group.

pub fn me(&self) -> usize

This node’s own index.

pub fn my_incarnation(&self) -> Incarnation

This node’s current incarnation.

pub fn nack_score(&self) -> u32

Current Lifeguard nack score (0 means “I believe I am healthy”).

pub fn status(&self, member: usize) -> Status

The internal SWIM status this node holds for member. Returns Status::Alive for me (a node always considers itself alive) and for any unknown index.

pub fn incarnation(&self, member: usize) -> Incarnation

The incarnation this node holds for member.

pub fn member_state(&self, member: usize) -> PeerState

Project the internal SWIM status onto the engine-wide PeerState the dispatcher consumes.

• Status::Alive -> PeerState::Normal
• Status::Suspect -> PeerState::Down (a suspect is removed from routing immediately; refutation restores it, exactly as phi-accrual’s transient down/up does)
• Status::Dead -> PeerState::Down

Mapping suspect to Down is deliberate: routing to a suspected-unreachable peer wastes a request, and a refutation promotes it straight back to Normal. The DST accuracy invariant is about the confirmed-dead status, not the transient suspect window.

pub fn on_probe( &mut self, tick: Tick, target: usize, result: ProbeResult, ) -> Vec<(u32, PeerState)>

Record the outcome of a probe period initiated by this node against target at logical tick.

• ProbeResult::Acked -> target confirmed alive; refresh its status and decay this node’s nack score.
• ProbeResult::IndirectAcked -> target alive, but this node’s direct path failed: raise the nack score (Lifeguard self-awareness) and keep the target alive.
• ProbeResult::Failed -> begin (or reinforce) suspicion of the target.

Returns any peer-state transitions the caller should apply.

pub fn on_update(&mut self, tick: Tick, update: Update) -> Vec<(u32, PeerState)>

Merge an incoming membership update that piggybacked on ping / ack traffic. Returns any peer-state transitions.

The merge rule is the SWIM precedence order:

• A higher incarnation always wins.
• At equal incarnation, Dead beats Suspect beats Alive (a worse belief overrides a better one at the same incarnation, which is how a suspicion spreads).
• An update about this node that suspects or kills it is refuted: this node bumps its own incarnation above the update and the refutation (a fresh Alive at the higher incarnation) is what the caller disseminates. Refutation is skipped when SwimConfig::refutation_enabled is false (negative-control only).

pub fn tick(&mut self, tick: Tick) -> Vec<(u32, PeerState)>

Advance logical time to tick and confirm any suspicions whose (dogpile- and NS-adjusted) deadline has passed. Returns the peer-state transitions produced (suspect -> dead is not a PeerState change, since both map to Down; the list is non-empty only when a member first crosses into Down).

pub fn confirm_deadline(&self, member: usize) -> Option<Tick>

The tick at which a suspicion of member will confirm dead, given the current suspector count and this node’s nack score. Returns None if the member is not currently suspect.

pub fn snapshot(&self) -> Vec<(usize, PeerState)>

Snapshot every member’s projected PeerState, for the I/O shell to reconcile against the pool.

Trait Implementations

impl Clone for SwimState

fn clone(&self) -> SwimState

Returns a duplicate of the value.

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

Performs copy-assignment from source.

impl Debug for SwimState

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

Formats the value using the given formatter.