Properly protect player struct with mutex

The volatile keyword neither guarantees atomic access nor memory
visibility[1]. Although this is usually not a problem on x86, it is
incorrect to rely on this. Use mutex locks to protect all shared player
variables and enforce memory visibility.

[1] https://wiki.sei.cmu.edu/confluence/display/c/CON02-C.+Do+not+use+volatile+as+a+synchronization+primitive

1 files changed, 9 insertions, 4 deletions

diff --git a/src/ui.c b/src/ui.c
index 0512f36..5c4e42d 100644
--- a/src/ui.c
+++ b/src/ui.c
@@ -1,5 +1,5 @@
 /*
-Copyright (c) 2008-2013
+Copyright (c) 2008-2018
 	Lars-Dominik Braun <lars@6xq.net>
 
 Permission is hereby granted, free of charge, to any person obtaining a copy
@@ -814,7 +814,7 @@ size_t BarUiListSongs (const BarApp_t * const app,
  */
 void BarUiStartEventCmd (const BarSettings_t *settings, const char *type,
 		const PianoStation_t *curStation, const PianoSong_t *curSong,
-		const player_t * const player, PianoStation_t *stations,
+		player_t * const player, PianoStation_t *stations,
 		PianoReturn_t pRet, CURLcode wRet) {
 	pid_t chld;
 	int pipeFd[2];
@@ -855,6 +855,11 @@ void BarUiStartEventCmd (const BarSettings_t *settings, const char *type,
 			songStation = PianoFindStationById (stations, curSong->stationId);
 		}
 
+		pthread_mutex_lock (&player->lock);
+		const unsigned int songDuration = player->songDuration;
+		const unsigned int songPlayed = player->songPlayed;
+		pthread_mutex_unlock (&player->lock);
+
 		fprintf (pipeWriteFd,
 				"artist=%s\n"
 				"title=%s\n"
@@ -880,8 +885,8 @@ void BarUiStartEventCmd (const BarSettings_t *settings, const char *type,
 				PianoErrorToStr (pRet),
 				wRet,
 				curl_easy_strerror (wRet),
-				player->songDuration,
-				player->songPlayed,
+				songDuration,
+				songPlayed,
 				curSong == NULL ? PIANO_RATE_NONE : curSong->rating,
 				curSong == NULL ? "" : curSong->detailUrl
 				);