test/uninit: add an "uninit" test

This is a weird example, where we don't explicitly initialize y, but
synchronization should guarantee that it is initialized.

Right now, this example has a problem where we never see flag == 2.

diff --git a/test/uninit.cc b/test/uninit.cc
new file mode 100644 (file)
index 0000000..edeae43
--- /dev/null
+++ b/test/uninit.cc
@@ -0,0 +1,57 @@
+/**
+ * @file uninit.cc
+ * @brief Uninitialized loads test
+ *
+ * This is a test of the "uninitialized loads" code. While we don't explicitly
+ * initialize y, this example's synchronization pattern should guarantee we
+ * never see it uninitialized.
+ *
+ * @todo (12/11/12) this example currently doesn't run properly; it never sees
+ * the behavior where 'flag == 2'.
+ */
+#include <stdio.h>
+#include <threads.h>
+#include <atomic>
+
+#include "librace.h"
+
+std::atomic_int x;
+std::atomic_int y;
+
+static void a(void *obj)
+{
+       int flag = x.load(std::memory_order_acquire);
+       printf("flag: %d\n", flag);
+       if (flag == 2)
+               printf("Load: %d\n", y.load(std::memory_order_relaxed));
+}
+
+static void b(void *obj)
+{
+       printf("fetch_add: %d\n", x.fetch_add(1, std::memory_order_relaxed));
+}
+
+static void c(void *obj)
+{
+       y.store(3, std::memory_order_relaxed);
+       x.store(1, std::memory_order_release);
+}
+
+int user_main(int argc, char **argv)
+{
+       thrd_t t1, t2, t3;
+
+       std::atomic_init(&x, 0);
+
+       printf("Thread %d: creating 2 threads\n", thrd_current());
+       thrd_create(&t1, (thrd_start_t)&a, NULL);
+       thrd_create(&t2, (thrd_start_t)&b, NULL);
+       thrd_create(&t3, (thrd_start_t)&c, NULL);
+
+       thrd_join(t1);
+       thrd_join(t2);
+       thrd_join(t3);
+       printf("Thread %d is finished\n", thrd_current());
+
+       return 0;
+}