audio: bug fix: suspend and resume player's stopwatches

Updates #2901

audio/audio.go

@@ -111,6 +111,9 @@ func NewContext(sampleRate int) *Context {
 		if err := c.playerFactory.suspend(); err != nil {
 			return err
 		}
+		if err := c.onSuspend(); err != nil {
+			return err
+		}
 		return nil
 	})
 	h.OnResumeAudio(func() error {
@@ -118,6 +121,9 @@ func NewContext(sampleRate int) *Context {
 		if err := c.playerFactory.resume(); err != nil {
 			return err
 		}
+		if err := c.onResume(); err != nil {
+			return err
+		}
 		return nil
 	})
 
@@ -197,6 +203,48 @@ func (c *Context) removePlayingPlayer(p *playerImpl) {
 	c.m.Unlock()
 }
 
+func (c *Context) onSuspend() error {
+	// A Context must not call playerImpl's functions with a lock, or this causes a deadlock (#2737).
+	// Copy the playerImpls and iterate them without a lock.
+	var players []*playerImpl
+	c.m.Lock()
+	players = make([]*playerImpl, 0, len(c.playingPlayers))
+	for p := range c.playingPlayers {
+		players = append(players, p)
+	}
+	c.m.Unlock()
+
+	for _, p := range players {
+		if err := p.Err(); err != nil {
+			return err
+		}
+		p.onContextSuspended()
+	}
+
+	return nil
+}
+
+func (c *Context) onResume() error {
+	// A Context must not call playerImpl's functions with a lock, or this causes a deadlock (#2737).
+	// Copy the playerImpls and iterate them without a lock.
+	var players []*playerImpl
+	c.m.Lock()
+	players = make([]*playerImpl, 0, len(c.playingPlayers))
+	for p := range c.playingPlayers {
+		players = append(players, p)
+	}
+	c.m.Unlock()
+
+	for _, p := range players {
+		if err := p.Err(); err != nil {
+			return err
+		}
+		p.onContextResumed()
+	}
+
+	return nil
+}
+
 func (c *Context) updatePlayers() error {
 	// A Context must not call playerImpl's functions with a lock, or this causes a deadlock (#2737).
 	// Copy the playerImpls and iterate them without a lock.

audio/player.go

@@ -326,6 +326,28 @@ func (p *playerImpl) source() io.Reader {
 	return p.src
 }
 
+func (p *playerImpl) onContextSuspended() {
+	p.m.Lock()
+	defer p.m.Unlock()
+
+	if p.player == nil {
+		return
+	}
+	p.stopwatch.stop()
+}
+
+func (p *playerImpl) onContextResumed() {
+	p.m.Lock()
+	defer p.m.Unlock()
+
+	if p.player == nil {
+		return
+	}
+	if p.isPlaying() {
+		p.stopwatch.start()
+	}
+}
+
 func (p *playerImpl) updatePosition() {
 	p.m.Lock()
 	defer p.m.Unlock()