Add queue_peek to the kernel (written by Mike Sevakis), and use it to improve upon my previous commit.

git-svn-id: svn://svn.rockbox.org/rockbox/trunk@15336 a1c6a512-1295-4272-9138-f99709370657

apps/playback.c

@@ -2569,6 +2569,7 @@ static void low_buffer_callback(void)
 
 static void audio_fill_file_buffer(bool start_play, size_t offset)
 {
+    struct queue_event ev;
     bool had_next_track = audio_next_track() != NULL;
     bool continue_buffering;
 
@@ -2591,9 +2592,14 @@ static void audio_fill_file_buffer(bool start_play, size_t offset)
         start_play = false;
         offset = 0;
         sleep(1);
-        if (!queue_empty(&audio_queue)) {
+        if (queue_peek(&audio_queue, &ev)) {
+            if (ev.id != Q_AUDIO_FILL_BUFFER)
+            {
                 /* There's a message in the queue. break the loop to treat it,
                 and go back to filling after that. */
+                LOGFQUEUE("buffering > audio Q_AUDIO_FILL_BUFFER");
+                queue_post(&audio_queue, Q_AUDIO_FILL_BUFFER, 0);
+            }
             break;
         }
     } while (continue_buffering);

firmware/export/kernel.h

@@ -219,6 +219,7 @@ extern void queue_reply(struct event_queue *q, intptr_t retval);
 extern bool queue_in_queue_send(struct event_queue *q);
 #endif /* HAVE_EXTENDED_MESSAGING_AND_NAME */
 extern bool queue_empty(const struct event_queue* q);
+extern bool queue_peek(struct event_queue *q, struct queue_event *ev);
 extern void queue_clear(struct event_queue* q);
 extern void queue_remove_from_head(struct event_queue *q, long id);
 extern int queue_count(const struct event_queue *q);

firmware/kernel.c

@@ -537,6 +537,28 @@ bool queue_empty(const struct event_queue* q)
     return ( q->read == q->write );
 }
 
+bool queue_peek(struct event_queue *q, struct queue_event *ev)
+{
+    if (q->read == q->write)
+         return false;
+
+    bool have_msg = false;
+
+    int oldlevel = set_irq_level(HIGHEST_IRQ_LEVEL);
+    corelock_lock(&q->cl);
+
+    if (q->read != q->write)
+    {
+        *ev = q->events[q->read & QUEUE_LENGTH_MASK];
+        have_msg = true;
+    }
+
+    corelock_unlock(&q->cl);
+    set_irq_level(oldlevel);
+
+    return have_msg;
+}
+
 void queue_clear(struct event_queue* q)
 {
     int oldlevel;

uisimulator/sdl/kernel.c

@@ -405,6 +405,26 @@ bool queue_empty(const struct event_queue* q)
     return ( q->read == q->write );
 }
 
+bool queue_peek(struct event_queue *q, struct queue_event *ev)
+{
+    if (q->read == q->write)
+         return false;
+
+    bool have_msg = false;
+
+    int oldlevel = set_irq_level(HIGHEST_IRQ_LEVEL);
+
+    if (q->read != q->write)
+    {
+        *ev = q->events[q->read & QUEUE_LENGTH_MASK];
+        have_msg = true;
+    }
+
+    set_irq_level(oldlevel);
+
+    return have_msg;
+}
+
 void queue_clear(struct event_queue* q)
 {
     int oldlevel = set_irq_level(HIGHEST_IRQ_LEVEL);