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//! Pub/sub fast-path methods on `Shard`. `SUBSCRIBE` / `UNSUBSCRIBE` /
//! `PUBLISH` and the per-loop publish-batch flush. Split out so [`crate::exec`]
//! stays under the 500-LOC house rule; everything is still on the same
//! `impl<C: Commands> Shard<C>`.
use crate::Commands;
use crate::message::{Agg, Inbound, Part, PendingSlot};
use crate::reduce::pubsub_message;
use crate::shard::Shard;
use kevy_resp::{ArgvView, encode_array_len, encode_bulk, encode_integer, encode_null_bulk};
impl<C: Commands> Shard<C> {
pub(crate) fn do_subscribe<A: ArgvView + ?Sized>(
&mut self,
conn_id: u64,
seq: u64,
args: &A,
subscribe: bool,
) {
let verb: &[u8] = if subscribe {
b"subscribe"
} else {
b"unsubscribe"
};
// Channels: the explicit args, or (UNSUBSCRIBE with none) all current subs.
let channels: Vec<Vec<u8>> = match self.conns.get(&conn_id) {
None => return,
Some(_) if args.len() > 1 => (1..args.len()).map(|i| args[i].to_vec()).collect(),
Some(c) => c.sub.iter().cloned().collect(),
};
let Some((reply, changed)) = self.apply_sub_to_conn(conn_id, &channels, subscribe, verb)
else {
return;
};
self.apply_sub_to_registry(&changed, subscribe);
if let Some(c) = self.conns.get_mut(&conn_id) {
c.pending.push_back(PendingSlot {
remaining: 1,
agg: Agg::First(None),
done: None,
});
}
self.fold(conn_id, seq, Part::Reply(reply));
}
/// Update the connection's local subscription set + build the
/// per-channel RESP reply. Returns `None` if the conn vanished
/// mid-flight, else `(reply_bytes, channels_that_actually_changed)`.
/// "Changed" matters because sub/unsub is idempotent — only real
/// transitions must update the shared registry.
fn apply_sub_to_conn(
&mut self,
conn_id: u64,
channels: &[Vec<u8>],
subscribe: bool,
verb: &[u8],
) -> Option<(Vec<u8>, Vec<Vec<u8>>)> {
let c = self.conns.get_mut(&conn_id)?;
let mut out = Vec::new();
let mut changed: Vec<Vec<u8>> = Vec::new();
if channels.is_empty() {
encode_array_len(&mut out, 3);
encode_bulk(&mut out, verb);
encode_null_bulk(&mut out);
encode_integer(&mut out, c.sub.len() as i64);
}
for ch in channels {
let did = if subscribe {
c.sub.insert(ch.clone())
} else {
c.sub.remove(ch)
};
if did {
changed.push(ch.clone());
}
encode_array_len(&mut out, 3);
encode_bulk(&mut out, verb);
encode_bulk(&mut out, ch);
encode_integer(&mut out, c.sub.len() as i64);
}
Some((out, changed))
}
/// Reflect a real (sub/unsub) transition into the cross-shard
/// registry that `PUBLISH` consults to route messages to the
/// shards that actually hold subscribers.
fn apply_sub_to_registry(&self, changed: &[Vec<u8>], subscribe: bool) {
if changed.is_empty() {
return;
}
let bit = 1u64 << self.id;
let mut reg = self.pubsub.write().expect("pubsub registry");
for ch in changed {
if subscribe {
let e = reg.entry(ch.clone()).or_insert((0, 0));
e.0 += 1;
e.1 |= bit;
} else {
let drop = match reg.get_mut(ch) {
Some(e) => {
e.0 = e.0.saturating_sub(1);
e.0 == 0
}
None => false,
};
if drop {
reg.remove(ch);
}
}
}
}
/// PUBLISH: reply with the receiver count read **locally** from the shared
/// registry (no cross-shard aggregation), then deliver the message
/// fire-and-forget to exactly the shards that hold a subscriber (in
/// parallel; no replies fold back). Replaces the old all-shards SumInt
/// fan-out, which cost ~2N cross-core ops per publish (N sends + N replies).
pub(crate) fn do_publish<A: ArgvView + ?Sized>(
&mut self,
conn_id: u64,
seq: u64,
args: &A,
) {
let (count, bits) = self
.pubsub
.read()
.expect("pubsub registry")
.get(&args[1])
.copied()
.unwrap_or((0, 0));
let mut reply = Vec::new();
encode_integer(&mut reply, count as i64);
if let Some(c) = self.conns.get_mut(&conn_id) {
c.pending.push_back(PendingSlot {
remaining: 1,
agg: Agg::First(None),
done: None,
});
}
self.fold(conn_id, seq, Part::Reply(reply));
if bits != 0 {
// Share one payload across all target shards (Arc, no per-target byte
// clone). Deliver locally inline; queue remote shards into per-target
// batches flushed once per drain (see `flush_publish`).
let m = std::sync::Arc::new((args[1].to_vec(), args[2].to_vec()));
for s in 0..self.nshards {
if bits & (1u64 << s) == 0 {
continue;
}
if s == self.id {
self.deliver_publish(&m.0, &m.1);
} else {
self.publish_batch[s].push(m.clone());
}
}
}
}
/// Append a pub/sub message to every local subscriber of `channel`; returns
/// the count delivered and marks them dirty for the reactor to flush.
pub(crate) fn deliver_publish(&mut self, channel: &[u8], msg: &[u8]) -> usize {
let ids: Vec<u64> = self
.conns
.iter()
.filter(|(_, c)| c.sub.contains(channel))
.map(|(id, _)| *id)
.collect();
if ids.is_empty() {
return 0;
}
let message = pubsub_message(channel, msg);
for id in &ids {
if let Some(c) = self.conns.get_mut(id) {
c.output.extend_from_slice(&message);
}
}
self.dirty.extend_from_slice(&ids);
ids.len()
}
/// Flush each shard's accumulated pub/sub batch as one cross-core message —
/// a flood of PUBLISHes costs one send per target shard per drain, not one
/// per message. Call once per reactor loop iteration.
#[inline]
pub(crate) fn flush_publish(&mut self) {
// Outer-empty short-circuit: the common hot path has no pub/sub.
if self.publish_batch.iter().all(|b| b.is_empty()) {
return;
}
for s in 0..self.nshards {
if s == self.id || self.publish_batch[s].is_empty() {
continue;
}
let batch = std::mem::take(&mut self.publish_batch[s]);
self.send_to(s, Inbound::DeliverPublish(batch));
}
}
}