Fix a deadlock between SpircManager and Player.

The player was invoking its observers with the state locked, and the
SpircManager’s registered observer would try to lock it again.

Instead, the observers are invoked with a cloned state, and the SpircManager
avoids locking the state again.

src/player.rs

@@ -20,6 +20,7 @@ pub struct Player {
     commands: mpsc::Sender<PlayerCommand>,
 }
 
+#[derive(Clone)]
 pub struct PlayerState {
     status: PlayStatus,
     position_ms: u32,
@@ -38,6 +39,7 @@ struct PlayerInternal {
     commands: mpsc::Receiver<PlayerCommand>,
 }
 
+#[derive(Debug)]
 enum PlayerCommand {
     Load(SpotifyId, bool, u32),
     Play,
@@ -102,8 +104,8 @@ impl Player {
         self.command(PlayerCommand::Seek(position_ms));
     }
 
-    pub fn state(&self) -> MutexGuard<PlayerState> {
-        self.state.lock().unwrap()
+    pub fn state(&self) -> PlayerState {
+        self.state.lock().unwrap().clone()
     }
 
     pub fn volume(&self, vol: u16) {
@@ -315,8 +317,11 @@ impl PlayerInternal {
         let observers = self.observers.lock().unwrap();
         if update {
             guard.update_time = util::now_ms();
+            let state = guard.clone();
+            drop(guard);
+
             for observer in observers.iter() {
-                observer(&guard);
+                observer(&state);
             }
         }
     }

src/spirc.rs

@@ -8,6 +8,7 @@ use util::version::version_string;
 use mercury::{MercuryRequest, MercuryMethod};
 use player::{Player, PlayerState};
 
+use std::borrow::Cow;
 use std::sync::{Mutex, Arc};
 use std::collections::HashMap;
 
@@ -420,8 +421,11 @@ impl<'a> CommandSender<'a> {
     }
 
     fn send(self) {
-        let internal_player_state = self.spirc_internal.player.state();
-        let s = self.player_state.unwrap_or(&*internal_player_state);
+        let state = self.player_state.map_or_else(|| {
+            Cow::Owned(self.spirc_internal.player.state())
+        }, |s| {
+            Cow::Borrowed(s)
+        });
 
         let mut pkt = protobuf_init!(protocol::spirc::Frame::new(), {
             version: 1,
@@ -432,12 +436,12 @@ impl<'a> CommandSender<'a> {
             recipient: RepeatedField::from_vec(
                 self.recipient.map(|r| vec![r.to_owned()] ).unwrap_or(vec![])
                 ),
-            device_state: self.spirc_internal.device_state(s),
-            state_update_id: s.update_time() as i64,
+            device_state: self.spirc_internal.device_state(&state),
+            state_update_id: state.update_time()
         });
 
         if self.spirc_internal.is_active {
-            pkt.set_state(self.spirc_internal.spirc_state(s));
+            pkt.set_state(self.spirc_internal.spirc_state(&state));
         }
 
         self.spirc_internal