add sequential consistency test

tests/mm_seq_cst.c

@@ -0,0 +1,115 @@
+
+#include <stdatomic.h>
+#include <threads.h>
+#include <stdio.h>
+
+#if 1
+    enum memory_order store_memory_order = memory_order_acquire;
+    enum memory_order load_memory_order = memory_order_release;
+#else
+    enum memory_order store_memory_order = memory_order_seq_cst;
+    enum memory_order load_memory_order = memory_order_seq_cst;
+#endif
+
+// Scheduler on linux has too coarse granularity
+// to allow a thread to a very tiny bit of work
+// before switching to another thread. If we
+// introduce an arbitrary delay, the threads will
+// be able to be run in a random order better.
+// Without it, the threads seem to be run as they are
+// created, i.e. the scheduling is too convenient and
+// hides a potential bug that we're testing for here
+#define delay_that_works 1000000
+#define arbitrary_delay(n) for(volatile int i = 0; i < n; ++i)
+
+// This is all the explicit shared state between threads.
+struct Shared_State typedef Shared_State;
+struct Shared_State {
+    _Atomic(int) x;
+    _Atomic(int) y;
+    _Atomic(int) cnt;
+};
+static Shared_State g_shared_state = {0};
+
+// Sets the atomic flag x
+int tx(void *ctx) {
+    arbitrary_delay(delay_that_works);
+    Shared_State *ss = ctx;
+    char msg[] = "Thread tx running\n";
+    fwrite(msg, 1, sizeof msg, stdout);
+    atomic_store_explicit(&ss->x, 1, store_memory_order);
+    return 0;
+}
+
+// Set the atomic flag y
+int ty(void *ctx) {
+    arbitrary_delay(delay_that_works);
+    Shared_State *ss = ctx;
+    char msg[] = "Thread ty running\n";
+    fwrite(msg, 1, sizeof msg, stdout);
+    atomic_store_explicit(&ss->y, 1, store_memory_order);
+    return 0;
+}
+
+// Spinlock until flag x is set, if y is also set, add 1 to cnt
+int t1(void *ctx) {
+    arbitrary_delay(delay_that_works);
+    Shared_State *ss = ctx;
+    char msg[] = "Thread t1 running\n";
+    fwrite(msg, 1, sizeof msg, stdout);
+    while(atomic_load_explicit(&ss->x, load_memory_order) == 0)
+        ;
+    if(atomic_load_explicit(&ss->y, load_memory_order) == 1) {
+        atomic_fetch_add_explicit(&ss->cnt, 1, memory_order_relaxed);
+    }
+    return 0;
+}
+
+// Spinlock until flag y is set, if x is also set, add 1 to cnt
+int t2(void *ctx) {
+    arbitrary_delay(delay_that_works);
+    Shared_State *ss = ctx;
+    char msg[] = "Thread t2 running\n";
+    fwrite(msg, 1, sizeof msg, stdout);
+    while(atomic_load_explicit(&ss->y, load_memory_order) == 0)
+        ;
+    if(atomic_load_explicit(&ss->x, load_memory_order) == 1) {
+        atomic_fetch_add_explicit(&ss->cnt, 1, memory_order_relaxed);
+    }
+    return 0;
+} 
+
+int main() {
+    // TODO: rewrite this to run in a loop after I
+    // fix stack leaking on thread destruction
+    thrd_start_t thread_funcs[4] = {tx,ty,t1,t2};
+    thrd_t threads[4];
+    // Spawn the threads
+    for(int i = 0; i < 4; ++i) {
+        int status = thrd_create(&threads[i], thread_funcs[i], &g_shared_state);
+        if(status != thrd_success) {
+            char msg[] = "Thread unable to start\n";
+            fwrite(msg, 1, sizeof msg, stdout);
+        }
+    }
+    // Wait for threads to complete
+    for(int i = 0; i < 4; ++i) {
+        int _exit_code;
+        thrd_join(threads[i], &_exit_code);
+    }
+    // Check to see the cnt variable
+    int result = atomic_load_explicit(&g_shared_state.cnt, memory_order_relaxed);
+    if(result == 0) {
+        char msg[] = "Result was 0\n";
+        fwrite(msg, 1, sizeof msg, stdout);
+    }
+    else if(result == 1) {
+        char msg[] = "Result was 1\n";
+        fwrite(msg, 1, sizeof msg, stdout);
+    }
+    else {
+        char msg[] = "Result was 2\n";
+        fwrite(msg, 1, sizeof msg, stdout);
+    }
+    return 0;
+}