libsaria: Notify UI when the idle queue size has changed

When the first task is queued, I trigger a callback so the UI can start
processing when idle.  I return the size of the queue from both
run_task() and queue_task() so the UI knows when to stop processing
callbacks.

include/libsaria/callback.h

@@ -5,6 +5,7 @@ enum callback_t {
 	PLAY,
 	PAUSE,
 	VOLUME,
+	IDLE_TASK_QUEUED,
 };
 
 void register_callback(callback_t, void (*)());

include/libsaria/idle.h

@@ -9,7 +9,7 @@ class IdleTask
 		virtual void run_task() = 0;
 };
 
-void libsaria_idle_task();
-void libsaria_queue_task(IdleTask *);
+int libsaria_idle_task();
+int libsaria_queue_task(IdleTask *);
 
 #endif /* LIBSARIA_IDLE_H */

libsaria/idle.cpp

@@ -1,19 +1,27 @@
 
+#include <libsaria/callback.h>
 #include "idle/idle.h"
 
 static Idle idle;
 
-void libsaria_idle_task()
+int libsaria_idle_task()
 {
-	idle.run_task();
+	return idle.run_task();
 }
 
 /*
  * This will queue a pre-constructed idle task
  * It should be constructed through `new` before calling
  * and will be deleted by the idle queue once run.
+ *
+ * IDLE_TASK_QUEUED will only be triggered when the queue
+ * goes from size is increased from 0 to 1.  This will tell
+ * the UI that idle tasks have been queued.
  */
-void libsaria_queue_task(IdleTask *task)
+int libsaria_queue_task(IdleTask *task)
 {
-	idle.queue_task(task);
+	int queue_size = idle.queue_task(task);
+	if (queue_size == 1)
+		trigger_callback(IDLE_TASK_QUEUED);
+	return queue_size;
 }

libsaria/idle/idle.cpp

@@ -10,18 +10,20 @@ Idle::~Idle()
 {
 }
 
-void Idle::run_task()
+int Idle::run_task()
 {
 	IdleTask *task;
 	if (idle_queue.size() == 0)
-		return;
+		return idle_queue.size();
 	task = idle_queue.front();
 	idle_queue.pop();
 	task->run_task();
 	delete task;
+	return idle_queue.size();
 }
 
-void Idle::queue_task(IdleTask *task)
+int Idle::queue_task(IdleTask *task)
 {
 	idle_queue.push(task);
+	return idle_queue.size();
 }

libsaria/idle/idle.h

@@ -15,8 +15,8 @@ class Idle
 		Idle();
 		~Idle();
 
-		void run_task();
-		void queue_task(IdleTask *);
+		int run_task();
+		int queue_task(IdleTask *);
 };
 
 #endif /* LIBSARIA_IDLE_COMPONENT_H */