Fix crash in dummy scheduler

examples/sched_ctx/dummy_sched_with_ctx.c

@@ -1,6 +1,6 @@
 /* StarPU --- Runtime system for heterogeneous multicore architectures.
  *
- * Copyright (C) 2010-2016  Université de Bordeaux
+ * Copyright (C) 2010-2017  Université de Bordeaux
  * Copyright (C) 2010-2013, 2016  CNRS
  *
  * StarPU is free software; you can redistribute it and/or modify
@@ -118,8 +118,14 @@ static struct starpu_task *pop_task_dummy(unsigned sched_ctx_id)
 	 * the calling worker. So we just take the head of the list and give it
 	 * to the worker. */
 	struct dummy_sched_data *data = (struct dummy_sched_data*)starpu_sched_ctx_get_policy_data(sched_ctx_id);
+#ifdef STARPU_NON_BLOCKING_DRIVERS
+	if (starpu_task_list_empty(&data->sched_list))
+		return NULL;
+#endif
 	STARPU_PTHREAD_MUTEX_LOCK(&data->policy_mutex);
-	struct starpu_task *task = starpu_task_list_pop_back(&data->sched_list);
+	struct starpu_task *task = NULL;
+	if (!starpu_task_list_empty(&data->sched_list))
+		task = starpu_task_list_pop_back(&data->sched_list);
 	STARPU_PTHREAD_MUTEX_UNLOCK(&data->policy_mutex);
 	return task;
 }

examples/scheduler/dummy_sched.c

@@ -1,6 +1,6 @@
 /* StarPU --- Runtime system for heterogeneous multicore architectures.
  *
- * Copyright (C) 2010-2016  Université de Bordeaux
+ * Copyright (C) 2010-2017  Université de Bordeaux
  * Copyright (C) 2010-2013, 2016  CNRS
  *
  * StarPU is free software; you can redistribute it and/or modify
@@ -122,7 +122,9 @@ static struct starpu_task *pop_task_dummy(unsigned sched_ctx_id)
 		return NULL;
 #endif
 	STARPU_PTHREAD_MUTEX_LOCK(&data->policy_mutex);
-	struct starpu_task *task = starpu_task_list_pop_back(&data->sched_list);
+	struct starpu_task *task = NULL;
+	if (!starpu_task_list_empty(&data->sched_list))
+		task = starpu_task_list_pop_back(&data->sched_list);
 	STARPU_PTHREAD_MUTEX_UNLOCK(&data->policy_mutex);
 	return task;
 }