test: mo-satcycle: add new MO satisfaction cycle example

See the comments at the top of the file.

diff --git a/test/mo-satcycle.cc b/test/mo-satcycle.cc
new file mode 100644 (file)
index 0000000..e502161
--- /dev/null
+++ b/test/mo-satcycle.cc
@@ -0,0 +1,68 @@
+/**
+ * @file mo-satcycle.cc
+ * @brief MO 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, y;
+int r0, r1, r2, r3; /* "local" variables */
+
+static void a(void *obj)
+{
+       y.store(10, memory_order_relaxed);
+       x.store(1, memory_order_release);
+}
+
+static void b(void *obj)
+{
+       r0 = x.load(memory_order_relaxed);
+       r1 = x.load(memory_order_acquire);
+       y.store(11, memory_order_relaxed);
+}
+
+static void c(void *obj)
+{
+       r2 = y.load(memory_order_relaxed);
+       r3 = y.load(memory_order_relaxed);
+       if (r2 == 11 && r3 == 10)
+               x.store(0, memory_order_relaxed);
+}
+
+int user_main(int argc, char **argv)
+{
+       thrd_t t1, t2, t3;
+
+       atomic_init(&x, 0);
+       atomic_init(&y, 0);
+
+       printf("Main thread: creating 3 threads\n");
+       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("Main thread is finished\n");
+
+       /*
+        * This condition should not be hit because it only occurs under a
+        * satisfaction cycle
+        */
+       bool cycle = (r0 == 1 && r1 == 0 && r2 == 11 && r3 == 10);
+       MODEL_ASSERT(!cycle);
+
+       return 0;
+}