Guard against multiple calls to fluid_player_seek()

Addresses #634

src/midi/fluid_midi.c

@@ -1646,7 +1646,7 @@ new_fluid_player(fluid_synth_t *synth)
         return NULL;
     }
 
-    player->status = FLUID_PLAYER_READY;
+    fluid_atomic_int_set(&player->status, FLUID_PLAYER_READY);
     player->loop = 1;
     player->ntracks = 0;
 
@@ -1798,7 +1798,7 @@ fluid_player_add_track(fluid_player_t *player, fluid_track_t *track)
 
 /**
  * Change the MIDI callback function. This is usually set to
- * fluid_synth_handle_midi_event, but can optionally be changed
+ * fluid_synth_handle_midi_event(), but can optionally be changed
  * to a user-defined function instead, for intercepting all MIDI
  * messages sent to the synth. You can also use a midi router as
  * the callback function to modify the MIDI messages before sending
@@ -2004,7 +2004,7 @@ fluid_player_playlist_load(fluid_player_t *player, unsigned int msec)
         if(player->currentfile == NULL)
         {
             /* Failed to find next song, probably since we're finished */
-            player->status = FLUID_PLAYER_DONE;
+            fluid_atomic_int_set(&player->status, FLUID_PLAYER_DONE);
             return;
         }
 
@@ -2050,7 +2050,7 @@ fluid_player_callback(void *data, unsigned int msec)
 
     loadnextfile = player->currentfile == NULL ? 1 : 0;
 
-    if(player->status == FLUID_PLAYER_DONE)
+    if(fluid_player_get_status(player) == FLUID_PLAYER_DONE)
     {
         fluid_synth_all_notes_off(synth, -1);
         return 1;
@@ -2108,7 +2108,7 @@ fluid_player_callback(void *data, unsigned int msec)
     }
     while(loadnextfile);
 
-    player->status = status;
+    fluid_atomic_int_set(&player->status, status);
 
     return 1;
 }
@@ -2121,7 +2121,7 @@ fluid_player_callback(void *data, unsigned int msec)
 int
 fluid_player_play(fluid_player_t *player)
 {
-    if(player->status == FLUID_PLAYER_PLAYING ||
+    if(fluid_player_get_status(player) == FLUID_PLAYER_PLAYING ||
        player->playlist == NULL)
     {
         return FLUID_OK;
@@ -2132,7 +2132,7 @@ fluid_player_play(fluid_player_t *player)
         fluid_sample_timer_reset(player->synth, player->sample_timer);
     }
 
-    player->status = FLUID_PLAYER_PLAYING;
+    fluid_atomic_int_set(&player->status, FLUID_PLAYER_PLAYING);
 
     return FLUID_OK;
 }
@@ -2146,7 +2146,7 @@ fluid_player_play(fluid_player_t *player)
 int
 fluid_player_stop(fluid_player_t *player)
 {
-    player->status = FLUID_PLAYER_DONE;
+    fluid_atomic_int_set(&player->status, FLUID_PLAYER_DONE);
     fluid_player_seek(player, fluid_player_get_current_tick(player));
     return FLUID_OK;
 }
@@ -2160,18 +2160,22 @@ fluid_player_stop(fluid_player_t *player)
 int
 fluid_player_get_status(fluid_player_t *player)
 {
-    return player->status;
+    return fluid_atomic_int_get(&player->status);
 }
 
 /**
  * Seek in the currently playing file.
+ *
+ * The actual seek will be performed when the synth calls back the player (i.e. a few
+ * levels above the player's callback set with fluid_player_set_playback_callback()).
+ * If the player's status is #FLUID_PLAYER_PLAYING and a previous seek operation has
+ * not been completed yet, #FLUID_FAILED is returned.
  * @param player MIDI player instance
  * @param ticks the position to seek to in the current file
- * @return #FLUID_FAILED if ticks is negative or after the latest tick of the file,
- *   #FLUID_OK otherwise
+ * @return #FLUID_FAILED if ticks is negative or after the latest tick of the file
+ * [or, since 2.1.3, if another seek operation is currently in progress],
+ * #FLUID_OK otherwise.
  * @since 2.0.0
- *
- * The actual seek is performed during the player_callback.
  */
 int fluid_player_seek(fluid_player_t *player, int ticks)
 {
@@ -2180,8 +2184,26 @@ int fluid_player_seek(fluid_player_t *player, int ticks)
         return FLUID_FAILED;
     }
 
-    fluid_atomic_int_set(&player->seek_ticks, ticks);
-    return FLUID_OK;
+    if(fluid_player_get_status(player) == FLUID_PLAYER_PLAYING)
+    {
+        if(fluid_atomic_int_compare_and_exchange(&player->seek_ticks, -1, ticks))
+        {
+            // new seek position has been set, as no previous seek was in progress
+            return FLUID_OK;
+        }
+    }
+    else
+    {
+        // If the player is not currently playing, a new seek position can be set at any time. This allows
+        // the user to do:
+        // fluid_player_stop();
+        // fluid_player_seek(0); // to beginning
+        fluid_atomic_int_set(&player->seek_ticks, ticks);
+        return FLUID_OK;
+    }
+
+    // a previous seek is still in progress or hasn't been processed yet
+    return FLUID_FAILED;
 }
 
 
@@ -2242,7 +2264,7 @@ int fluid_player_set_bpm(fluid_player_t *player, int bpm)
 int
 fluid_player_join(fluid_player_t *player)
 {
-    while(player->status != FLUID_PLAYER_DONE)
+    while(fluid_player_get_status(player) != FLUID_PLAYER_DONE)
     {
         fluid_msleep(10);
     }

src/midi/fluid_midi.h

@@ -272,7 +272,7 @@ typedef struct
  */
 struct _fluid_player_t
 {
-    int status;
+    fluid_atomic_int_t status;
     int ntracks;
     fluid_track_t *track[MAX_NUMBER_OF_TRACKS];
     fluid_synth_t *synth;