From: Brian Norris <banorris@uci.edu>
Date: Wed, 3 Oct 2012 19:07:33 +0000 (-0700)
Subject: model: JOIN/LOCK unification
X-Git-Tag: pldi2013~71
X-Git-Url: http://plrg.eecs.uci.edu/git/?p=model-checker.git;a=commitdiff_plain;h=5d87d23f622d396fd2e1c94d61f901429c5f35ac

model: JOIN/LOCK unification

Make join and lock actions use similar code paths.

This used to trigger a bug, due to the lack of a private snapshotting
heap.
---

diff --git a/model.cc b/model.cc
index 02f290d..e11dcf7 100644
--- a/model.cc
+++ b/model.cc
@@ -557,26 +557,17 @@ bool ModelChecker::process_thread_action(ModelAction *curr)
 		break;
 	}
 	case THREAD_JOIN: {
-		Thread *waiting, *blocking;
-		waiting = get_thread(curr);
-		blocking = (Thread *)curr->get_location();
-		if (!blocking->is_complete()) {
-			blocking->push_wait_list(curr);
-			scheduler->sleep(waiting);
-		} else {
-			do_complete_join(curr);
-			updated = true; /* trigger rel-seq checks */
-		}
+		Thread *blocking = (Thread *)curr->get_location();
+		ModelAction *act = get_last_action(blocking->get_id());
+		curr->synchronize_with(act);
+		updated = true; /* trigger rel-seq checks */
 		break;
 	}
 	case THREAD_FINISH: {
 		Thread *th = get_thread(curr);
 		while (!th->wait_list_empty()) {
 			ModelAction *act = th->pop_wait_list();
-			Thread *wake = get_thread(act);
-			scheduler->wake(wake);
-			do_complete_join(act);
-			updated = true; /* trigger rel-seq checks */
+			scheduler->wake(get_thread(act));
 		}
 		th->complete();
 		updated = true; /* trigger rel-seq checks */
@@ -721,9 +712,12 @@ ModelAction * ModelChecker::initialize_curr_action(ModelAction *curr)
 }
 
 /**
- * This method checks whether a model action is enabled at the given point.
- * At this point, it checks whether a lock operation would be successful at this point.
- * If not, it puts the thread in a waiter list.
+ * @brief Check whether a model action is enabled.
+ *
+ * Checks whether a lock or join operation would be successful (i.e., is the
+ * lock already locked, or is the joined thread already complete). If not, put
+ * the action in a waiter list.
+ *
  * @param curr is the ModelAction to check whether it is enabled.
  * @return a bool that indicates whether the action is enabled.
  */
@@ -736,6 +730,12 @@ bool ModelChecker::check_action_enabled(ModelAction *curr) {
 			lock_waiters_map->get_safe_ptr(curr->get_location())->push_back(curr);
 			return false;
 		}
+	} else if (curr->get_type() == THREAD_JOIN) {
+		Thread *blocking = (Thread *)curr->get_location();
+		if (!blocking->is_complete()) {
+			blocking->push_wait_list(curr);
+			return false;
+		}
 	}
 
 	return true;
@@ -760,7 +760,7 @@ Thread * ModelChecker::check_current_action(ModelAction *curr)
 
 	if (!check_action_enabled(curr)) {
 		/* Make the execution look like we chose to run this action
-		 * much later, when a lock is actually available to release */
+		 * much later, when a lock/join can succeed */
 		get_current_thread()->set_pending(curr);
 		scheduler->sleep(get_current_thread());
 		return get_next_thread(NULL);
@@ -847,19 +847,6 @@ Thread * ModelChecker::check_current_action(ModelAction *curr)
 	return get_next_thread(curr);
 }
 
-/**
- * Complete a THREAD_JOIN operation, by synchronizing with the THREAD_FINISH
- * operation from the Thread it is joining with. Must be called after the
- * completion of the Thread in question.
- * @param join The THREAD_JOIN action
- */
-void ModelChecker::do_complete_join(ModelAction *join)
-{
-	Thread *blocking = (Thread *)join->get_location();
-	ModelAction *act = get_last_action(blocking->get_id());
-	join->synchronize_with(act);
-}
-
 void ModelChecker::check_curr_backtracking(ModelAction * curr) {
 	Node *currnode = curr->get_node();
 	Node *parnode = currnode->get_parent();
diff --git a/model.h b/model.h
index c99e0f8..6e470c0 100644
--- a/model.h
+++ b/model.h
@@ -169,7 +169,6 @@ private:
 	bool w_modification_order(ModelAction *curr);
 	bool release_seq_heads(const ModelAction *rf, rel_heads_list_t *release_heads, struct release_seq *pending) const;
 	bool resolve_release_sequences(void *location, work_queue_t *work_queue);
-	void do_complete_join(ModelAction *join);
 
 	ModelAction *diverge;
 	ModelAction *earliest_diverge;