GThreadPool: Add some queue manipulation api

GTask has a need for an api that boosts an unprocessed
item to the front of the queue, so add one.

https://bugzilla.gnome.org/show_bug.cgi?id=751160

docs/reference/glib/glib-sections.txt

@@ -827,6 +827,7 @@ g_thread_pool_stop_unused_threads
 g_thread_pool_set_sort_function
 g_thread_pool_set_max_idle_time
 g_thread_pool_get_max_idle_time
+g_thread_pool_move_to_front
 </SECTION>
 
 <SECTION>

glib/gthreadpool.c

@@ -962,6 +962,36 @@ g_thread_pool_set_sort_function (GThreadPool      *pool,
   g_async_queue_unlock (real->queue);
 }
 
+/**
+ * g_thread_pool_move_to_front:
+ * @pool: a #GThreadPool
+ * @data: an unprocessed item in the pool
+ *
+ * Moves the item to the front of the queue of unprocessed
+ * items, so that it will be processed next.
+ *
+ * Returns: %TRUE if the item was found and moved
+ *
+ * Since: 2.46
+ */
+gboolean
+g_thread_pool_move_to_front (GThreadPool *pool,
+                             gpointer     data)
+{
+  GRealThreadPool *real = (GRealThreadPool*) pool;
+  gboolean found;
+
+  g_async_queue_lock (real->queue);
+
+  found = g_async_queue_remove_unlocked (real->queue, data);
+  if (found)
+    g_async_queue_push_front_unlocked (real->queue, data);
+
+  g_async_queue_unlock (real->queue);
+
+  return found;
+}
+
 /**
  * g_thread_pool_set_max_idle_time:
  * @interval: the maximum @interval (in milliseconds)

glib/gthreadpool.h

@@ -65,6 +65,10 @@ GLIB_AVAILABLE_IN_ALL
 void            g_thread_pool_set_sort_function (GThreadPool      *pool,
                                                  GCompareDataFunc  func,
                                                  gpointer          user_data);
+GLIB_AVAILABLE_IN_2_46
+gboolean        g_thread_pool_move_to_front     (GThreadPool      *pool,
+                                                 gpointer          data);
+
 GLIB_AVAILABLE_IN_ALL
 gboolean        g_thread_pool_set_max_threads   (GThreadPool     *pool,
                                                  gint             max_threads,