atomic example

~/C/atomic.c

@@ -0,0 +1,30 @@
+#include <stdio.h>
+#include <threads.h>
+#include <stdatomic.h>
+
+atomic_int acnt;
+int cnt;
+
+int f(void* thr_data)
+{
+    (void)thr_data;
+    for(int n = 0; n < 1000; ++n) {
+        ++cnt;
+        ++acnt;
+        // for this example, relaxed memory order is sufficient, e.g.
+        // atomic_fetch_add_explicit(&acnt, 1, memory_order_relaxed);
+    }
+    return 0;
+}
+
+int main(void)
+{
+    thrd_t thr[10];
+    for(int n = 0; n < 10; ++n)
+        thrd_create(&thr[n], f, NULL);
+    for(int n = 0; n < 10; ++n)
+        thrd_join(thr[n], NULL);
+
+    printf("The atomic counter is %u\n", acnt);
+    printf("The non-atomic counter is %u\n", cnt);
+}