Struct Shard 

struct Shard {
    cur: Arc<Mutex<Option<Arc<Open>>>>,
    ask: Sender<Sender<Option<Arc<Open>>>>,
}

Where the read path asks one flusher shard for a readable copy of its open block (section 4), and where the last copy it produced is cached.

The snapshot is taken on demand, never on a timer: an idle node with nobody querying it copies nothing. A Mutex around the cached Arc rather than an ArcSwap — the critical section is one pointer clone and a crate for that would be a crate for nothing.

Fields

cur: Arc<Mutex<Option<Arc<Open>>>>

ask: Sender<Sender<Option<Arc<Open>>>>

Handing the flusher somewhere to put an answer. Not generic in the signal’s request type, which is the whole reason the read path can hold three of these in one array.

Implementations

impl Shard

fn get(&self) -> Option<Arc<Open>>

The last snapshot taken, without asking for a new one.

fn put(&self, v: Option<Arc<Open>>)

fn lock(&self) -> MutexGuard<'_, Option<Arc<Open>>>

A panic in this critical section is not possible — it clones or drops an Arc and nothing else — so poisoning carries no information and unwrapping it would only turn an impossible bug into an outage.

Trait Implementations

impl Clone for Shard

fn clone(&self) -> Shard

Returns a duplicate of the value.

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

Performs copy-assignment from source.