mediaplayer: Improve MPD failure handling

Changes:
- Avoid crashing in the MPD event handler code when our connection
  times out because it has hung.  Additionally, attempt to update
  the front end UI to a sane state with respect to metadata when
  this happens.
- Lower the MPD connection timeout and keepalive timeouts to try to
  catch MPD failures faster.  There are still problems in this area
  with respect to the front end UI getting stuck if it does an
  operation that would attempt to use the MPD API while it is hung.
  Fixing that completely would require a significant refactoring to
  move all the MPD API code to a separate thread so that the QML
  rendering thread does not get stuck.  It's unclear at present if
  such a refactoring is justified, as the MPD hang in this case is
  fixed by changes in MPD 0.23.8.

Bug-AGL: SPEC-4661

Signed-off-by: Scott Murray <scott.murray@konsulko.com>
Change-Id: Ia5e74d00acdc6b3b28cdf87b26486dbddfa02a98

1 files changed, 52 insertions, 30 deletions

diff --git a/mediaplayer/MediaplayerMpdBackend.cpp b/mediaplayer/MediaplayerMpdBackend.cpp
index 5cc9dce..8ffb346 100644
--- a/mediaplayer/MediaplayerMpdBackend.cpp
+++ b/mediaplayer/MediaplayerMpdBackend.cpp
@@ -19,14 +19,15 @@
 #include "MpdEventHandler.h"
 #include "mediaplayer.h"
 
-// Use a 60s timeout on our MPD connection
+// Use a 30s timeout on our MPD connection
 // NOTE: The connection is actively poked at a higher frequency than
 //       this to ensure we don't hit the timeout.  The alternatives
 //       are to either open and close a connection for every command,
 //       or try to keep the connection in idle mode when not using it.
 //       The latter is deemed too complicated for our purposes for now,
 //       due to it likely requiring another thread.
-#define MPD_CONNECTION_TIMEOUT	60000
+#define MPD_CONNECTION_TIMEOUT	30000
+#define MPD_KEEPALIVE_TIMEOUT	5000
 
 MediaplayerMpdBackend::MediaplayerMpdBackend(Mediaplayer *player, QQmlContext *context, QObject *parent) :
 	MediaplayerBackend(player, parent)
@@ -43,7 +44,7 @@ MediaplayerMpdBackend::MediaplayerMpdBackend(Mediaplayer *player, QQmlContext *c
 	// Set up connection keepalive timer
 	m_mpd_conn_timer = new QTimer(this);
 	connect(m_mpd_conn_timer, &QTimer::timeout, this, &MediaplayerMpdBackend::connectionKeepaliveTimeout);
-	m_mpd_conn_timer->start(MPD_CONNECTION_TIMEOUT / 2);
+	m_mpd_conn_timer->start(MPD_KEEPALIVE_TIMEOUT);
 
 	m_song_pos_timer = new QTimer(this);
 	connect(m_song_pos_timer, &QTimer::timeout, this, &MediaplayerMpdBackend::songPositionTimeout);
@@ -57,6 +58,7 @@ MediaplayerMpdBackend::MediaplayerMpdBackend(Mediaplayer *player, QQmlContext *c
 	// Create thread to handle polling for MPD events
 	MpdEventHandler *handler = new MpdEventHandler();
 	handler->moveToThread(&m_handlerThread);
+	connect(&m_handlerThread, &QThread::finished, this, &MediaplayerMpdBackend::handleHandlerFinish);
 	connect(&m_handlerThread, &QThread::finished, handler, &QObject::deleteLater);
 	connect(this,
 		&MediaplayerMpdBackend::startHandler,
@@ -169,25 +171,37 @@ void MediaplayerMpdBackend::connectionKeepaliveTimeout(void)
 	m_mpd_conn_mutex.lock();
 
 	// Clear any lingering non-fatal errors
-	if (!mpd_connection_clear_error(m_mpd_conn)) {
+	if (m_mpd_conn && !mpd_connection_clear_error(m_mpd_conn)) {
 		// NOTE: There should likely be an attempt to reconnect here,
 		//       but it definitely would complicate things for all the
 		//       other users.
 		qWarning() << "MPD connection in error state!";
-		m_mpd_conn_mutex.unlock();
-		return;
+		mpd_connection_free(m_mpd_conn);
+		m_mpd_conn = NULL;
+		m_mpd_conn_timer->stop();
 	}
+	m_mpd_conn_mutex.unlock();
+}
 
-	struct mpd_status *status = mpd_run_status(m_mpd_conn);
-	if (!status) {
-		qWarning() << "MPD connection status check failed";
-	} else {
-		mpd_status_free(status);
-	}
+void MediaplayerMpdBackend::handleHandlerFinish(void)
+{
+	m_mpd_conn_mutex.lock();
+
+	// If the event thread finished, our connection is likely dead.
+	// Given the behavior seen when mpd is hung is most client API
+	// calls hang, trying to determine mpd liveliness here seems
+	// problematic. Attempting to reconnect would probably be the
+	// only robust solution.
+	mpd_connection_free(m_mpd_conn);
+	m_mpd_conn = NULL;
 
 	m_mpd_conn_mutex.unlock();
+
+	m_mpd_conn_timer->stop();
+	delete m_mpd_conn_timer;
 }
 
+
 void MediaplayerMpdBackend::songPositionTimeout(void)
 {
 	m_state_mutex.lock();
@@ -271,7 +285,7 @@ void MediaplayerMpdBackend::play()
 	m_mpd_conn_mutex.lock();
 
 	m_state_mutex.lock();
-	if (!m_playing) {
+	if (m_mpd_conn && !m_playing) {
 		mpd_run_play(m_mpd_conn);
 	}
 	m_state_mutex.unlock();
@@ -284,7 +298,7 @@ void MediaplayerMpdBackend::pause()
 	m_mpd_conn_mutex.lock();
 
 	m_state_mutex.lock();
-	if (m_playing) {
+	if (m_mpd_conn && m_playing) {
 		mpd_run_pause(m_mpd_conn, true);
 	}
 	m_state_mutex.unlock();
@@ -298,7 +312,7 @@ void MediaplayerMpdBackend::previous()
 
 	// MPD only allows next/previous if playing
 	m_state_mutex.lock();
-	if (m_playing) {
+	if (m_mpd_conn && m_playing) {
 		mpd_run_previous(m_mpd_conn);
 	}
 	m_state_mutex.unlock();
@@ -312,7 +326,7 @@ void MediaplayerMpdBackend::next()
 
 	// MPD only allows next/previous if playing
 	m_state_mutex.lock();
-	if (m_playing) {
+	if (m_mpd_conn && m_playing) {
 		mpd_run_next(m_mpd_conn);
 	}
 	m_state_mutex.unlock();
@@ -324,9 +338,11 @@ void MediaplayerMpdBackend::seek(int milliseconds)
 {
 	m_mpd_conn_mutex.lock();
 
-	float t = milliseconds;
-	t /= 1000.0;
-	mpd_run_seek_current(m_mpd_conn, t, false);
+	if (m_mpd_conn) {
+		float t = milliseconds;
+		t /= 1000.0;
+		mpd_run_seek_current(m_mpd_conn, t, false);
+	}
 
 	m_mpd_conn_mutex.unlock();
 }
@@ -336,9 +352,11 @@ void MediaplayerMpdBackend::fastforward(int milliseconds)
 {
 	m_mpd_conn_mutex.lock();
 
-	float t = milliseconds;
-	t /= 1000.0;
-	mpd_run_seek_current(m_mpd_conn, t, true);
+	if (m_mpd_conn) {
+		float t = milliseconds;
+		t /= 1000.0;
+		mpd_run_seek_current(m_mpd_conn, t, true);
+	}
 
 	m_mpd_conn_mutex.unlock();
 }
@@ -348,9 +366,11 @@ void MediaplayerMpdBackend::rewind(int milliseconds)
 {
 	m_mpd_conn_mutex.lock();
 
-	float t = -milliseconds;
-	t /= 1000.0;
-	mpd_run_seek_current(m_mpd_conn, t, true);
+	if (m_mpd_conn) {
+		float t = -milliseconds;
+		t /= 1000.0;
+		mpd_run_seek_current(m_mpd_conn, t, true);
+	}
 
 	m_mpd_conn_mutex.unlock();
 }
@@ -359,7 +379,7 @@ void MediaplayerMpdBackend::picktrack(int track)
 {
 	m_mpd_conn_mutex.lock();
 
-	if (track >= 0) {
+	if (m_mpd_conn && track >= 0) {
 		mpd_run_play_pos(m_mpd_conn, track);
 	}
 
@@ -383,10 +403,12 @@ void MediaplayerMpdBackend::loop(QString state)
 	// mpd_run_single_state(m_mpd_conn, MPD_SINGLE_OFF) (default)
 	// mpd_run_repeat(m_mpd_conn, true) to loop
 
-	if (state == "playlist") {
-		mpd_run_repeat(m_mpd_conn, true);
-	} else {
-		mpd_run_repeat(m_mpd_conn, false);
+	if (m_mpd_conn) {
+		if (state == "playlist") {
+			mpd_run_repeat(m_mpd_conn, true);
+		} else {
+			mpd_run_repeat(m_mpd_conn, false);
+		}
 	}
 
 	m_mpd_conn_mutex.unlock();