model: enforce rule: current_action != NULL

Now that I've fixed THREAD_JOIN, modify the comments and safety checks.

diff --git a/model.cc b/model.cc
index d171ad0b83a7a97b86caa6e9aed48ea1c1411378..0bb96175eff46b3cfc00b8d926b13055ff8e9c9a 100644 (file)
--- a/model.cc
+++ b/model.cc
@@ -953,10 +953,7 @@ void ModelChecker::remove_thread(Thread *t)
  * context). This switch is made with the intention of exploring a particular
  * model-checking action (described by a ModelAction object). Must be called
  * from a user-thread context.
- * @param act The current action that will be explored. May be NULL, although
- * there is little reason to switch to the model-checker without an action to
- * explore (note: act == NULL is sometimes used as a hack to allow a thread to
- * yield control without performing any progress; see thrd_join()).
+ * @param act The current action that will be explored. Must not be NULL.
  * @return Return status from the 'swap' call (i.e., success/fail, 0/-1)
  */
 int ModelChecker::switch_to_master(ModelAction *act)
@@ -978,10 +975,9 @@ bool ModelChecker::take_step() {
        curr = thread_current();
        if (curr) {
                if (curr->get_state() == THREAD_READY) {
-                       if (current_action) {
-                               nextThread = check_current_action(current_action);
-                               current_action = NULL;
-                       }
+                       ASSERT(current_action);
+                       nextThread = check_current_action(current_action);
+                       current_action = NULL;
                        if (!curr->is_blocked())
                                scheduler->add_thread(curr);
                } else if (curr->get_state() == THREAD_RUNNING) {