1use collections::{BTreeMap, BTreeSet};
  2use parking_lot::Mutex;
  3use std::{fmt::Debug, mem, sync::Arc};
  4use util::post_inc;
  5
  6pub(crate) struct SubscriberSet<EmitterKey, Callback>(
  7    Arc<Mutex<SubscriberSetState<EmitterKey, Callback>>>,
  8);
  9
 10impl<EmitterKey, Callback> Clone for SubscriberSet<EmitterKey, Callback> {
 11    fn clone(&self) -> Self {
 12        SubscriberSet(self.0.clone())
 13    }
 14}
 15
 16struct SubscriberSetState<EmitterKey, Callback> {
 17    subscribers: BTreeMap<EmitterKey, BTreeMap<usize, Callback>>,
 18    dropped_subscribers: BTreeSet<(EmitterKey, usize)>,
 19    next_subscriber_id: usize,
 20}
 21
 22impl<EmitterKey, Callback> SubscriberSet<EmitterKey, Callback>
 23where
 24    EmitterKey: 'static + Send + Ord + Clone + Debug,
 25    Callback: 'static + Send,
 26{
 27    pub fn new() -> Self {
 28        Self(Arc::new(Mutex::new(SubscriberSetState {
 29            subscribers: Default::default(),
 30            dropped_subscribers: Default::default(),
 31            next_subscriber_id: 0,
 32        })))
 33    }
 34
 35    pub fn insert(&self, emitter_key: EmitterKey, callback: Callback) -> Subscription {
 36        let mut lock = self.0.lock();
 37        let subscriber_id = post_inc(&mut lock.next_subscriber_id);
 38        lock.subscribers
 39            .entry(emitter_key.clone())
 40            .or_default()
 41            .insert(subscriber_id, callback);
 42        let this = self.0.clone();
 43        Subscription {
 44            unsubscribe: Some(Box::new(move || {
 45                let mut lock = this.lock();
 46                if let Some(subscribers) = lock.subscribers.get_mut(&emitter_key) {
 47                    subscribers.remove(&subscriber_id);
 48                    if subscribers.is_empty() {
 49                        lock.subscribers.remove(&emitter_key);
 50                        return;
 51                    }
 52                }
 53
 54                // We didn't manage to remove the subscription, which means it was dropped
 55                // while invoking the callback. Mark it as dropped so that we can remove it
 56                // later.
 57                lock.dropped_subscribers
 58                    .insert((emitter_key, subscriber_id));
 59            })),
 60        }
 61    }
 62
 63    pub fn remove(&self, emitter: &EmitterKey) -> impl IntoIterator<Item = Callback> {
 64        let subscribers = self.0.lock().subscribers.remove(&emitter);
 65        subscribers.unwrap_or_default().into_values()
 66    }
 67
 68    pub fn retain<F>(&self, emitter: &EmitterKey, mut f: F)
 69    where
 70        F: FnMut(&mut Callback) -> bool,
 71    {
 72        let entry = self.0.lock().subscribers.remove_entry(emitter);
 73        if let Some((emitter, mut subscribers)) = entry {
 74            subscribers.retain(|_, callback| f(callback));
 75            let mut lock = self.0.lock();
 76
 77            // Add any new subscribers that were added while invoking the callback.
 78            if let Some(new_subscribers) = lock.subscribers.remove(&emitter) {
 79                subscribers.extend(new_subscribers);
 80            }
 81
 82            // Remove any dropped subscriptions that were dropped while invoking the callback.
 83            for (dropped_emitter, dropped_subscription_id) in
 84                mem::take(&mut lock.dropped_subscribers)
 85            {
 86                debug_assert_eq!(emitter, dropped_emitter);
 87                subscribers.remove(&dropped_subscription_id);
 88            }
 89
 90            if !subscribers.is_empty() {
 91                lock.subscribers.insert(emitter, subscribers);
 92            }
 93        }
 94    }
 95}
 96
 97#[must_use]
 98pub struct Subscription {
 99    unsubscribe: Option<Box<dyn FnOnce() + Send + 'static>>,
100}
101
102impl Subscription {
103    pub fn detach(mut self) {
104        self.unsubscribe.take();
105    }
106}
107
108impl Drop for Subscription {
109    fn drop(&mut self) {
110        if let Some(unsubscribe) = self.unsubscribe.take() {
111            unsubscribe();
112        }
113    }
114}