accounts: update EventEmitter on add_account (#2559)

* accounts: update EventEmitter on add_account

* accounts: do not lock waiting for EventEmitter in dc_accounts_add_account

Otherwise dc_accounts_add_account blocks until an event arrives on
some existing account.

src/accounts.rs

@@ -1,5 +1,6 @@
 use std::collections::BTreeMap;
 
+use async_std::channel::{Receiver, Sender};
 use async_std::fs;
 use async_std::path::PathBuf;
 use async_std::prelude::*;
@@ -18,6 +19,7 @@ pub struct Accounts {
     dir: PathBuf,
     config: Config,
     accounts: Arc<RwLock<BTreeMap<u32, Context>>>,
+    emitter: EventEmitter,
 }
 
 impl Accounts {
@@ -52,10 +54,16 @@ impl Accounts {
         let config = Config::from_file(config_file).await?;
         let accounts = config.load_accounts().await?;
 
+        let emitter = EventEmitter::new();
+        for account in accounts.values() {
+            emitter.add_account(account).await?;
+        }
+
         Ok(Self {
             dir,
             config,
             accounts: Arc::new(RwLock::new(accounts)),
+            emitter,
         })
     }
 
@@ -83,6 +91,7 @@ impl Accounts {
         let account_config = self.config.new_account(&self.dir).await?;
 
         let ctx = Context::new(os_name, account_config.dbfile().into(), account_config.id).await?;
+        self.emitter.add_account(&ctx).await?;
         self.accounts.write().await.insert(account_config.id, ctx);
 
         Ok(account_config.id)
@@ -228,30 +237,60 @@ impl Accounts {
 
     /// Unified event emitter.
     pub async fn get_event_emitter(&self) -> EventEmitter {
-        let emitters: Vec<_> = self
-            .accounts
-            .read()
-            .await
-            .iter()
-            .map(|(_id, a)| a.get_event_emitter())
-            .collect();
-
-        EventEmitter(futures::stream::select_all(emitters))
+        self.emitter.clone()
     }
 }
 
-#[derive(Debug)]
-pub struct EventEmitter(futures::stream::SelectAll<crate::events::EventEmitter>);
+#[derive(Debug, Clone)]
+pub struct EventEmitter {
+    /// Aggregate stream of events from all accounts.
+    stream: Arc<RwLock<futures::stream::SelectAll<crate::events::EventEmitter>>>,
+
+    /// Sender for the channel where new account emitters will be pushed.
+    sender: Sender<crate::events::EventEmitter>,
+
+    /// Receiver for the channel where new account emitters will be pushed.
+    receiver: Receiver<crate::events::EventEmitter>,
+}
 
 impl EventEmitter {
-    /// Blocking recv of an event. Return `None` if all `Sender`s have been droped.
-    pub fn recv_sync(&mut self) -> Option<Event> {
-        async_std::task::block_on(self.recv())
+    pub fn new() -> Self {
+        let (sender, receiver) = async_std::channel::unbounded();
+        Self {
+            stream: Arc::new(RwLock::new(futures::stream::SelectAll::new())),
+            sender,
+            receiver,
+        }
     }
 
-    /// Async recv of an event. Return `None` if all `Sender`s have been droped.
-    pub async fn recv(&mut self) -> Option<Event> {
-        self.0.next().await
+    /// Blocking recv of an event. Return `None` if all `Sender`s have been droped.
+    pub fn recv_sync(&mut self) -> Option<Event> {
+        async_std::task::block_on(self.recv()).unwrap_or_default()
+    }
+
+    /// Async recv of an event. Return `None` if all `Sender`s have been dropped.
+    pub async fn recv(&mut self) -> Result<Option<Event>> {
+        let mut stream = self.stream.write().await;
+        loop {
+            match futures::future::select(self.receiver.recv(), stream.next()).await {
+                futures::future::Either::Left((emitter, _)) => {
+                    stream.push(emitter?);
+                }
+                futures::future::Either::Right((ev, _)) => return Ok(ev),
+            }
+        }
+    }
+
+    /// Add event emitter of a new account to the aggregate event emitter.
+    pub async fn add_account(&self, context: &Context) -> Result<()> {
+        self.sender.send(context.get_event_emitter()).await?;
+        Ok(())
+    }
+}
+
+impl Default for EventEmitter {
+    fn default() -> Self {
+        Self::new()
     }
 }
 
@@ -262,7 +301,7 @@ impl async_std::stream::Stream for EventEmitter {
         mut self: std::pin::Pin<&mut Self>,
         cx: &mut std::task::Context<'_>,
     ) -> std::task::Poll<Option<Self::Item>> {
-        std::pin::Pin::new(&mut self.0).poll_next(cx)
+        std::pin::Pin::new(&mut self).poll_next(cx)
     }
 }