test: addr-satcycle: add new address-based sat. cycle example

See the comments and assertion in the program for the description.

diff --git a/test/addr-satcycle.cc b/test/addr-satcycle.cc
new file mode 100644 (file)
index 0000000..0d3ba5a
--- /dev/null
+++ b/test/addr-satcycle.cc
@@ -0,0 +1,67 @@
+/**
+ * @file addr-satcycle.cc
+ * @brief Address-based satisfaction cycle test
+ *
+ * This program has a peculiar behavior which is technically legal under the
+ * current C++ memory model but which is a result of a type of satisfaction
+ * cycle. We use this as justification for part of our modifications to the
+ * memory model when proving our model-checker's correctness.
+ */
+
+#include <atomic>
+#include <threads.h>
+#include <stdio.h>
+
+#include "model-assert.h"
+
+using namespace std;
+
+atomic_int x[2], idx, y;
+
+int r1, r2, r3; /* "local" variables */
+
+static void a(void *obj)
+{
+       r1 = idx.load(memory_order_relaxed);
+       x[r1].store(0, memory_order_relaxed);
+
+       /* Key point: can we guarantee that &x[0] == &x[r1]? */
+       r2 = x[0].load(memory_order_relaxed);
+       y.store(r2);
+}
+
+static void b(void *obj)
+{
+       r3 = y.load(memory_order_relaxed);
+       idx.store(r3, memory_order_relaxed);
+}
+
+int user_main(int argc, char **argv)
+{
+       thrd_t t1, t2;
+
+       atomic_init(&x[0], 1);
+       atomic_init(&idx, 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");
+
+       printf("r1 = %d\n", r1);
+       printf("r2 = %d\n", r2);
+       printf("r3 = %d\n", r3);
+
+       /*
+        * This condition should not be hit because it only occurs under a
+        * satisfaction cycle
+        */
+       bool cycle = (r1 == 1 && r2 == 1 && r3 == 1);
+       MODEL_ASSERT(!cycle);
+
+       return 0;
+}