Struct HistoryCacheStats 

pub struct HistoryCacheStats {
    pub len: AtomicUsize,
    pub evicted: AtomicU64,
    pub max_sn: AtomicI64,
    pub min_sn: AtomicI64,
}

Atomically updated snapshot statistics of a HistoryCache.

Note: the actual BTreeMap storage of the cache still needs &mut self to mutate (concurrent read/write BTreeMap mutation does not exist in std), but statistics values (length, max/min SN, eviction counter) are carried in parallel in an Arc<HistoryCacheStats>. Monitoring threads, SEDP tick loops and telemetry can thus poll lock-free, without taking the writer/reader lock.

Consistency guarantee: every mutating method of the cache updates the atomics after the BTreeMap mutation, with Release ordering. Readers use Acquire ordering — they see a consistent state of the last completed cache operation, never a half-updated state of the individual atomics.

What is not guaranteed: cross-field consistency. If a reader reads len and then max_sn, further inserts can have happened between the loads. That is acceptable for monitoring; for hard wire paths (heartbeat build) the writer lock is still taken.

Fields

len: AtomicUsize

Number of changes in the cache (corresponds to BTreeMap::len).

evicted: AtomicU64

Number of samples discarded by KeepLast eviction since start.

max_sn: AtomicI64

Highest SN in the cache, or [STATS_SENTINEL_NO_SN] if empty.

min_sn: AtomicI64

Lowest SN in the cache, or [STATS_SENTINEL_NO_SN] if empty.

Implementations

impl HistoryCacheStats

pub fn snapshot(&self) -> HistoryCacheSnapshot

Snapshot of the four atomics as a plain-old-data struct. Loaded with Acquire ordering — synchronized with the Release store in HistoryCache::insert / HistoryCache::remove_up_to.

Trait Implementations

impl Clone for HistoryCacheStats

fn clone(&self) -> Self

Returns a duplicate of the value.

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

Performs copy-assignment from source.

impl Debug for HistoryCacheStats

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

Formats the value using the given formatter.

impl Default for HistoryCacheStats

fn default() -> Self

Returns the “default value” for a type.