From: Brian Norris <banorris@uci.edu>
Date: Wed, 7 Nov 2012 03:18:34 +0000 (-0800)
Subject: model: add deadlock detection
X-Git-Url: http://demsky.eecs.uci.edu/git/?a=commitdiff_plain;h=3cf4799ac961046bb2464ae1b6ee72f064d94716;p=cdsspec-compiler.git

model: add deadlock detection

This is only a simple end-of-execution deadlock detection. If we have a
true deadlock, and no other threads are spinning, then our execution
will exit --- we can recognize this state.

For more complicated deadlocks involving other spinning threads, we need
to perform some sort of depth-first-search cycle detection.
---

diff --git a/model.cc b/model.cc
index ff1fdf9..94620ea 100644
--- a/model.cc
+++ b/model.cc
@@ -244,6 +244,26 @@ void ModelChecker::wake_up_sleeping_actions(ModelAction * curr) {
 	}
 }
 
+/**
+ * Check if we are in a deadlock. Should only be called at the end of an
+ * execution, although it should not give false positives in the middle of an
+ * execution (there should be some ENABLED thread).
+ *
+ * @return True if program is in a deadlock; false otherwise
+ */
+bool ModelChecker::is_deadlocked() const
+{
+	bool blocking_threads = false;
+	for (unsigned int i = 0; i < get_num_threads(); i++) {
+		Thread *t = get_thread(int_to_id(i));
+		if (scheduler->is_enabled(t) != THREAD_DISABLED)
+			return false;
+		else if (!t->is_model_thread() && t->get_pending())
+			blocking_threads = true;
+	}
+	return blocking_threads;
+}
+
 /**
  * Queries the model-checker for more executions to explore and, if one
  * exists, resets the model-checker state to execute a new execution.
@@ -257,6 +277,8 @@ bool ModelChecker::next_execution()
 
 	num_executions++;
 
+	if (is_deadlocked())
+		printf("ERROR: DEADLOCK\n");
 	if (isfinalfeasible()) {
 		printf("Earliest divergence point since last feasible execution:\n");
 		if (earliest_diverge)
diff --git a/model.h b/model.h
index 3ef6ee3..6d702b0 100644
--- a/model.h
+++ b/model.h
@@ -115,6 +115,7 @@ public:
 	void finish_execution();
 	bool isfeasibleprefix();
 	void set_assert() {asserted=true;}
+	bool is_deadlocked() const;
 
 	/** @brief Alert the model-checker that an incorrectly-ordered
 	 * synchronization was made */