From: Brian Norris <banorris@uci.edu>
Date: Tue, 3 Jul 2012 23:31:45 +0000 (-0700)
Subject: threads: add per-thread "return" values for 'model-checking/user context' switch
X-Git-Tag: pldi2013~378
X-Git-Url: http://demsky.eecs.uci.edu/git/?a=commitdiff_plain;h=85c090982c2a8dd6e236aa8f3d0a79f974ab9603;p=model-checker.git

threads: add per-thread "return" values for 'model-checking/user context' switch

The model-checker needs to return a value to the user context when performing
atomic loads, for instance. I will be implementing this by caching the return
value on a per-thread basis. This is because an atomic_load() might result in a
context switch before actually returning the value.

These functions are not yet used.
---

diff --git a/threads.cc b/threads.cc
index 6d290a9..b6eaee4 100644
--- a/threads.cc
+++ b/threads.cc
@@ -69,7 +69,9 @@ void Thread::complete()
 	}
 }
 
-Thread::Thread(thrd_t *t, void (*func)(void *), void *a) {
+Thread::Thread(thrd_t *t, void (*func)(void *), void *a) :
+	last_action_val(VALUE_NONE)
+{
 	int ret;
 
 	user_thread = t;
diff --git a/threads.h b/threads.h
index a97a04c..ed9cbfe 100644
--- a/threads.h
+++ b/threads.h
@@ -41,6 +41,21 @@ public:
 	void set_creation(ModelAction *act) { creation = act; }
 	ModelAction * get_creation() { return creation; }
 
+	/**
+	 * Set a return value for the last action in this thread (e.g., for an
+	 * atomic read).
+	 * @param value The value to return
+	 */
+	void set_return_value(int value) { last_action_val = value; }
+
+	/**
+	 * Retrieve a return value for the last action in this thread. Used,
+	 * for instance, for an atomic read to return the 'read' value. Should
+	 * be called from a user context.
+	 * @return The value 'returned' by the action
+	 */
+	int get_return_value() { return last_action_val; }
+
 	friend void thread_startup();
 
 	SNAPSHOTALLOC
@@ -56,6 +71,13 @@ private:
 	thrd_t *user_thread;
 	thread_id_t id;
 	thread_state state;
+
+	/**
+	 * The value returned by the last action in this thread
+	 * @see Thread::set_return_value()
+	 * @see Thread::get_return_value()
+	 */
+	int last_action_val;
 };
 
 Thread * thread_current();