K2V: Subscription to ranges of items

src/model/k2v/sub.rs

@@ -0,0 +1,107 @@
+use std::collections::HashMap;
+use std::sync::Mutex;
+
+use serde::{Deserialize, Serialize};
+use tokio::sync::broadcast;
+
+use crate::k2v::item_table::*;
+
+#[derive(Debug, Hash, Clone, PartialEq, Eq, Serialize, Deserialize)]
+pub struct PollKey {
+	pub partition: K2VItemPartition,
+	pub sort_key: String,
+}
+
+#[derive(Debug, Hash, Clone, PartialEq, Eq, Serialize, Deserialize)]
+pub struct PollRange {
+	pub partition: K2VItemPartition,
+	pub prefix: Option<String>,
+	pub start: Option<String>,
+	pub end: Option<String>,
+}
+
+#[derive(Default)]
+pub struct SubscriptionManager(Mutex<SubscriptionManagerInner>);
+
+#[derive(Default)]
+pub struct SubscriptionManagerInner {
+	item_subscriptions: HashMap<PollKey, broadcast::Sender<K2VItem>>,
+	range_subscriptions: HashMap<PollRange, broadcast::Sender<K2VItem>>,
+}
+
+impl SubscriptionManager {
+	pub fn new() -> Self {
+		Self::default()
+	}
+
+	pub fn subscribe_item(&self, key: &PollKey) -> broadcast::Receiver<K2VItem> {
+		let mut inner = self.0.lock().unwrap();
+		if let Some(s) = inner.item_subscriptions.get(key) {
+			s.subscribe()
+		} else {
+			let (tx, rx) = broadcast::channel(8);
+			inner.item_subscriptions.insert(key.clone(), tx);
+			rx
+		}
+	}
+
+	pub fn subscribe_range(&self, key: &PollRange) -> broadcast::Receiver<K2VItem> {
+		let mut inner = self.0.lock().unwrap();
+		if let Some(s) = inner.range_subscriptions.get(key) {
+			s.subscribe()
+		} else {
+			let (tx, rx) = broadcast::channel(8);
+			inner.range_subscriptions.insert(key.clone(), tx);
+			rx
+		}
+	}
+
+	pub fn notify(&self, item: &K2VItem) {
+		let mut inner = self.0.lock().unwrap();
+
+		// 1. Notify single item subscribers,
+		// removing subscriptions with no more listeners if any
+		let key = PollKey {
+			partition: item.partition.clone(),
+			sort_key: item.sort_key.clone(),
+		};
+		if let Some(s) = inner.item_subscriptions.get(&key) {
+			if s.send(item.clone()).is_err() {
+				// no more subscribers, remove channel from here
+				// (we will re-create it later if we need to subscribe again)
+				inner.item_subscriptions.remove(&key);
+			}
+		}
+
+		// 2. Notify range subscribers,
+		// removing subscriptions with no more listeners if any
+		inner.range_subscriptions.retain(|sub, chan| {
+			if sub.matches(&item) {
+				chan.send(item.clone()).is_ok()
+			} else {
+				chan.receiver_count() != 0
+			}
+		});
+	}
+}
+
+impl PollRange {
+	fn matches(&self, item: &K2VItem) -> bool {
+		item.partition == self.partition
+			&& self
+				.prefix
+				.as_ref()
+				.map(|x| item.sort_key.starts_with(x))
+				.unwrap_or(true)
+			&& self
+				.start
+				.as_ref()
+				.map(|x| item.sort_key >= *x)
+				.unwrap_or(true)
+			&& self
+				.end
+				.as_ref()
+				.map(|x| item.sort_key < *x)
+				.unwrap_or(true)
+	}
+}