model/threads: add documentation comments

[model-checker.git] / model.cc

diff --git a/model.cc b/model.cc
index f5dd7cbda419209acf023c27d340218d146ebcff..856a33d2cdfa13d2db741797d4fc0f1681a9fd04 100644 (file)
--- a/model.cc
+++ b/model.cc
@@ -39,7 +39,6 @@ struct bug_message {
  */
 struct model_snapshot_members {
        model_snapshot_members() :
-               current_action(NULL),
                /* First thread created will have id INITIAL_THREAD_ID */
                next_thread_id(INITIAL_THREAD_ID),
                used_sequence_numbers(0),
@@ -59,7 +58,6 @@ struct model_snapshot_members {
                bugs.clear();
        }
 
-       ModelAction *current_action;
        unsigned int next_thread_id;
        modelclock_t used_sequence_numbers;
        ModelAction *next_backtrack;
@@ -161,6 +159,14 @@ void ModelChecker::reset_to_initial_state()
        /* Print all model-checker output before rollback */
        fflush(model_out);
 
+       /**
+        * FIXME: if we utilize partial rollback, we will need to free only
+        * those pending actions which were NOT pending before the rollback
+        * point
+        */
+       for (unsigned int i = 0; i < get_num_threads(); i++)
+               delete get_thread(int_to_id(i))->get_pending();
+
        snapshot_backtrack_before(0);
 }
 
@@ -218,7 +224,7 @@ Thread * ModelChecker::get_next_thread(ModelAction *curr)
        if (curr != NULL) {
                /* Do not split atomic actions. */
                if (curr->is_rmwr())
-                       return thread_current();
+                       return get_thread(curr);
                else if (curr->get_type() == THREAD_CREATE)
                        return curr->get_thread_operand();
        }
@@ -295,11 +301,8 @@ void ModelChecker::execute_sleep_set()
        for (unsigned int i = 0; i < get_num_threads(); i++) {
                thread_id_t tid = int_to_id(i);
                Thread *thr = get_thread(tid);
-               if (scheduler->is_sleep_set(thr) && thr->get_pending() == NULL) {
-                       scheduler->next_thread(thr);
-                       Thread::swap(&system_context, thr);
-                       priv->current_action->set_sleep_flag();
-                       thr->set_pending(priv->current_action);
+               if (scheduler->is_sleep_set(thr) && thr->get_pending()) {
+                       thr->get_pending()->set_sleep_flag();
                }
        }
 }
@@ -324,11 +327,22 @@ void ModelChecker::set_bad_synchronization()
        priv->bad_synchronization = true;
 }
 
+/**
+ * Check whether the current trace has triggered an assertion which should halt
+ * its execution.
+ *
+ * @return True, if the execution should be aborted; false otherwise
+ */
 bool ModelChecker::has_asserted() const
 {
        return priv->asserted;
 }
 
+/**
+ * Trigger a trace assertion which should cause this execution to be halted.
+ * This can be due to a detected bug or due to an infeasibility that should
+ * halt ASAP.
+ */
 void ModelChecker::set_assert()
 {
        priv->asserted = true;
@@ -1215,16 +1229,6 @@ bool ModelChecker::check_action_enabled(ModelAction *curr) {
        return true;
 }
 
-/**
- * Stores the ModelAction for the current thread action.  Call this
- * immediately before switching from user- to system-context to pass
- * data between them.
- * @param act The ModelAction created by the user-thread action
- */
-void ModelChecker::set_current_action(ModelAction *act) {
-       priv->current_action = act;
-}
-
 /**
  * This is the heart of the model checker routine. It performs model-checking
  * actions corresponding to a given "current action." Among other processes, it
@@ -2678,7 +2682,8 @@ uint64_t ModelChecker::switch_to_master(ModelAction *act)
 {
        DBG();
        Thread *old = thread_current();
-       set_current_action(act);
+       ASSERT(!old->get_pending());
+       old->set_pending(act);
        if (Thread::swap(old, &system_context) < 0) {
                perror("swap threads");
                exit(EXIT_FAILURE);
@@ -2694,9 +2699,6 @@ uint64_t ModelChecker::switch_to_master(ModelAction *act)
  */
 Thread * ModelChecker::take_step(ModelAction *curr)
 {
-       if (has_asserted())
-               return NULL;
-
        Thread *curr_thrd = get_thread(curr);
        ASSERT(curr_thrd->get_state() == THREAD_READY);
 
@@ -2738,7 +2740,7 @@ Thread * ModelChecker::take_step(ModelAction *curr)
                ModelAction *fixup = new ModelAction(MODEL_FIXUP_RELSEQ,
                                std::memory_order_seq_cst, NULL, VALUE_NONE,
                                model_thread);
-               set_current_action(fixup);
+               model_thread->set_pending(fixup);
                return model_thread;
        }
 
@@ -2746,13 +2748,6 @@ Thread * ModelChecker::take_step(ModelAction *curr)
        if (!next_thrd)
                return NULL;
 
-       if (next_thrd->get_pending() != NULL) {
-               /* restart a pending action */
-               set_current_action(next_thrd->get_pending());
-               next_thrd->set_pending(NULL);
-               return next_thrd;
-       }
-
        return next_thrd;
 }
 
@@ -2771,9 +2766,30 @@ void ModelChecker::run()
                add_thread(t);
 
                do {
-                       scheduler->next_thread(t);
-                       Thread::swap(&system_context, t);
-                       t = take_step(priv->current_action);
+                       /*
+                        * Stash next pending action(s) for thread(s). There
+                        * should only need to stash one thread's action--the
+                        * thread which just took a step--plus the first step
+                        * for any newly-created thread
+                        */
+                       for (unsigned int i = 0; i < get_num_threads(); i++) {
+                               thread_id_t tid = int_to_id(i);
+                               Thread *thr = get_thread(tid);
+                               if (!thr->is_model_thread() && !thr->is_complete() && !thr->get_pending()) {
+                                       scheduler->next_thread(thr);
+                                       Thread::swap(&system_context, thr);
+                               }
+                       }
+
+                       /* Catch assertions from prior take_step or from
+                        * between-ModelAction bugs (e.g., data races) */
+                       if (has_asserted())
+                               break;
+
+                       /* Consume the next action for a Thread */
+                       ModelAction *curr = t->get_pending();
+                       t->set_pending(NULL);
+                       t = take_step(curr);
                } while (t && !t->is_model_thread());
                /** @TODO Re-write release sequence fixups here */
        } while (next_execution());