test: add double-read-fv

This test fails (!) because we never see r1 = r2 = 42.

diff --git a/test/double-read-fv.c b/test/double-read-fv.c
new file mode 100755 (executable)
index 0000000..120cdc3
--- /dev/null
+++ b/test/double-read-fv.c
@@ -0,0 +1,50 @@
+/*
+ * Try to read the same value as a future value twice.
+ *
+ * This test should be able to see r1 = r2 = 42. Currently, we never see that
+ * (as of 2/21/13) because the r2 load won't have a potential future value of
+ * 42 at the same time as r1, due to our scheduling (the loads for r1 and r2
+ * must occur before the write of x = 42).
+ *
+ * Note that the atomic_int y is simply used to aid in forcing a particularly
+ * interesting scheduling. It is superfluous.
+ */
+#include <stdio.h>
+#include <threads.h>
+#include <stdatomic.h>
+
+#include "librace.h"
+
+atomic_int x;
+atomic_int y;
+
+static void a(void *obj)
+{
+       int r1 = atomic_load_explicit(&x, memory_order_relaxed);
+       int r2 = atomic_load_explicit(&x, memory_order_relaxed);
+       printf("r1 = %d, r2 = %d\n", r1, r2);
+}
+
+static void b(void *obj)
+{
+       atomic_store_explicit(&y, 43, memory_order_relaxed);
+       atomic_store_explicit(&x, 42, memory_order_relaxed);
+}
+
+int user_main(int argc, char **argv)
+{
+       thrd_t t1, t2;
+
+       atomic_init(&x, 0);
+       atomic_init(&y, 0);
+
+       printf("Main thread: creating 2 threads\n");
+       thrd_create(&t1, (thrd_start_t)&a, NULL);
+       thrd_create(&t2, (thrd_start_t)&b, NULL);
+
+       thrd_join(t1);
+       thrd_join(t2);
+       printf("Main thread is finished\n");
+
+       return 0;
+}