model: refactor the get_thread() selection

get_thread() may or may not be called with a non-NULL 'curr' argument,
and if it non-NULL, it still may not be used. Make the logic cleaner by
pulling the 'curr'-specific functionality out to its own function.

diff --git a/model.cc b/model.cc
index 0a5cda59df858e8d4f35e74e7eb76929032bbefa..d15a094f7d8049e1a1e81ed8ac78527b6d1ca66a 100644 (file)
--- a/model.cc
+++ b/model.cc
@@ -204,34 +204,43 @@ Node * ModelChecker::get_curr_node() const
        return node_stack->get_head();
 }
 
+/**
+ * @brief Select the next thread to execute based on the curren action
+ *
+ * RMW actions occur in two parts, and we cannot split them. And THREAD_CREATE
+ * actions should be followed by the execution of their child thread. In either
+ * case, the current action should determine the next thread schedule.
+ *
+ * @param curr The current action
+ * @return The next thread to run, if the current action will determine this
+ * selection; otherwise NULL
+ */
+Thread * ModelChecker::action_select_next_thread(const ModelAction *curr) const
+{
+       /* Do not split atomic RMW */
+       if (curr->is_rmwr())
+               return get_thread(curr);
+       /* Follow CREATE with the created thread */
+       if (curr->get_type() == THREAD_CREATE)
+               return curr->get_thread_operand();
+       return NULL;
+}
+
 /**
  * @brief Choose the next thread to execute.
  *
- * This function chooses the next thread that should execute. It can force the
- * adjacency of read/write portions of a RMW action, force THREAD_CREATE to be
- * followed by a THREAD_START, or it can enforce execution replay/backtracking.
- * The model-checker may have no preference regarding the next thread (i.e.,
- * when exploring a new execution ordering), in which case we defer to the
- * scheduler.
+ * This function chooses the next thread that should execute. It can enforce
+ * execution replay/backtracking or, if the model-checker has no preference
+ * regarding the next thread (i.e., when exploring a new execution ordering),
+ * we defer to the scheduler.
  *
- * @param curr Optional: The current ModelAction. Only used if non-NULL and it
- * might guide the choice of next thread (i.e., THREAD_CREATE should be
- * followed by THREAD_START, or ATOMIC_RMWR followed by ATOMIC_{RMW,RMWC})
- * @return The next chosen thread to run, if any exist. Or else if no threads
- * remain to be executed, return NULL.
+ * @return The next chosen thread to run, if any exist. Or else if the current
+ * execution should terminate, return NULL.
  */
-Thread * ModelChecker::get_next_thread(ModelAction *curr)
+Thread * ModelChecker::get_next_thread()
 {
        thread_id_t tid;
 
-       if (curr != NULL) {
-               /* Do not split atomic actions. */
-               if (curr->is_rmwr())
-                       return get_thread(curr);
-               else if (curr->get_type() == THREAD_CREATE)
-                       return curr->get_thread_operand();
-       }
-
        /*
         * Have we completed exploring the preselected path? Then let the
         * scheduler decide
@@ -3026,7 +3035,11 @@ Thread * ModelChecker::take_step(ModelAction *curr)
        if (curr_thrd->is_blocked() || curr_thrd->is_complete())
                scheduler->remove_thread(curr_thrd);
 
-       Thread *next_thrd = get_next_thread(curr);
+       Thread *next_thrd = NULL;
+       if (curr)
+               next_thrd = action_select_next_thread(curr);
+       if (!next_thrd)
+               next_thrd = get_next_thread();
 
        DEBUG("(%d, %d)\n", curr_thrd ? id_to_int(curr_thrd->get_id()) : -1,
                        next_thrd ? id_to_int(next_thrd->get_id()) : -1);

diff --git a/model.h b/model.h
index ae668b159cb04d701ff151f099b96c85ae2452a0..c368ce6ef9cc7ca937cf78b580de1b5a80a6dd9d 100644 (file)
--- a/model.h
+++ b/model.h
@@ -176,7 +176,8 @@ private:
        ModelAction * get_last_fence_conflict(ModelAction *act) const;
        ModelAction * get_last_conflict(ModelAction *act) const;
        void set_backtracking(ModelAction *act);
-       Thread * get_next_thread(ModelAction *curr);
+       Thread * action_select_next_thread(const ModelAction *curr) const;
+       Thread * get_next_thread();
        bool set_latest_backtrack(ModelAction *act);
        ModelAction * get_next_backtrack();
        void reset_to_initial_state();