Write docs for subscriptions and reorganize a bit

winit/src/subscription.rs

@@ -0,0 +1,97 @@
+use iced_native::{Event, Hasher, Subscription};
+use std::collections::HashMap;
+
+pub struct Pool {
+    alive: HashMap<u64, Handle>,
+}
+
+pub struct Handle {
+    _cancel: futures::channel::oneshot::Sender<()>,
+    listener: Option<futures::channel::mpsc::Sender<Event>>,
+}
+
+impl Pool {
+    pub fn new() -> Self {
+        Self {
+            alive: HashMap::new(),
+        }
+    }
+
+    pub fn update<Message: Send>(
+        &mut self,
+        subscription: Subscription<Message>,
+        thread_pool: &mut futures::executor::ThreadPool,
+        proxy: &winit::event_loop::EventLoopProxy<Message>,
+    ) {
+        use futures::{future::FutureExt, stream::StreamExt};
+
+        let recipes = subscription.recipes();
+        let mut alive = std::collections::HashSet::new();
+
+        for recipe in recipes {
+            let id = {
+                use std::hash::Hasher as _;
+
+                let mut hasher = Hasher::default();
+                recipe.hash(&mut hasher);
+
+                hasher.finish()
+            };
+
+            let _ = alive.insert(id);
+
+            if !self.alive.contains_key(&id) {
+                let (cancel, cancelled) = futures::channel::oneshot::channel();
+
+                // TODO: Use bus if/when it supports async
+                let (event_sender, event_receiver) =
+                    futures::channel::mpsc::channel(100);
+
+                let stream = recipe.stream(event_receiver.boxed());
+                let proxy = proxy.clone();
+
+                let future = futures::future::select(
+                    cancelled,
+                    stream.for_each(move |message| {
+                        proxy
+                            .send_event(message)
+                            .expect("Send subscription result to event loop");
+
+                        futures::future::ready(())
+                    }),
+                )
+                .map(|_| ());
+
+                thread_pool.spawn_ok(future);
+
+                let _ = self.alive.insert(
+                    id,
+                    Handle {
+                        _cancel: cancel,
+                        listener: if event_sender.is_closed() {
+                            None
+                        } else {
+                            Some(event_sender)
+                        },
+                    },
+                );
+            }
+        }
+
+        self.alive.retain(|id, _| alive.contains(&id));
+    }
+
+    pub fn broadcast_event(&mut self, event: Event) {
+        self.alive
+            .values_mut()
+            .filter_map(|connection| connection.listener.as_mut())
+            .for_each(|listener| {
+                if let Err(error) = listener.try_send(event) {
+                    log::warn!(
+                        "Error sending event to subscription: {:?}",
+                        error
+                    );
+                }
+            });
+    }
+}