decoder_control: add function _is_current_song()

Replaces _current_song().

src/decoder_control.c

@@ -97,6 +97,27 @@ dc_command_async(struct decoder_control *dc, enum decoder_command cmd)
 	decoder_unlock(dc);
 }
 
+bool
+decoder_is_current_song(const struct decoder_control *dc,
+			const struct song *song)
+{
+	assert(dc != NULL);
+	assert(song != NULL);
+
+	switch (dc->state) {
+	case DECODE_STATE_STOP:
+	case DECODE_STATE_ERROR:
+		return false;
+
+	case DECODE_STATE_START:
+	case DECODE_STATE_DECODE:
+		return dc->song == song;
+	}
+
+	assert(false);
+	return false;
+}
+
 void
 dc_start(struct decoder_control *dc, struct song *song,
 	 unsigned start_ms, unsigned end_ms,

src/decoder_control.h

@@ -276,21 +276,27 @@ decoder_lock_has_failed(struct decoder_control *dc)
 	return ret;
 }
 
-static inline const struct song *
-decoder_current_song(const struct decoder_control *dc)
+/**
+ * Check if the specified song is currently being decoded.  If the
+ * decoder is not running currently (or being started), then this
+ * function returns false in any case.
+ *
+ * Caller must lock the object.
+ */
+gcc_pure
+bool
+decoder_is_current_song(const struct decoder_control *dc,
+			const struct song *song);
+
+gcc_pure
+static inline bool
+decoder_lock_is_current_song(struct decoder_control *dc,
+			     const struct song *song)
 {
-	switch (dc->state) {
-	case DECODE_STATE_STOP:
-	case DECODE_STATE_ERROR:
-		return NULL;
-
-	case DECODE_STATE_START:
-	case DECODE_STATE_DECODE:
-		return dc->song;
-	}
-
-	assert(false);
-	return NULL;
+	decoder_lock(dc);
+	const bool result = decoder_is_current_song(dc, song);
+	decoder_unlock(dc);
+	return result;
 }
 
 /**

src/player_thread.c

@@ -458,7 +458,7 @@ static bool player_seek_decoder(struct player *player)
 
 	assert(pc->next_song != NULL);
 
-	if (decoder_current_song(dc) != song) {
+	if (!decoder_lock_is_current_song(dc, song)) {
 		/* the decoder is already decoding the "next" song -
 		   stop it and start the previous song again */