packed_array: add a little atomic access logic

1 files changed, 6 insertions, 3 deletions

diff --git a/packed_array.hpp b/packed_array.hpp
index 9fb2c59..f4fa041 100644
--- a/packed_array.hpp
+++ b/packed_array.hpp
@@ -18,9 +18,12 @@ struct packed_array {
     element(word_t *base, uint shift) : base(base), shift(shift) {}
 
     T operator= (T val) {
-      word_t mask = ~(((((word_t) 1) << bit_sz) - 1) << shift);
-      *base &= mask;
-      *base ^= val << shift;
+      word_t old_val, new_val;
+      do {
+	word_t mask = ~(((((word_t) 1) << bit_sz) - 1) << shift);
+	old_val = *((volatile word_t*) base);
+	new_val = (old_val & mask) ^ (val << shift);
+      } while (!__sync_bool_compare_and_swap(base, old_val, new_val));
       return val;
     }