From 4bccf8848a3410795ab66d7f615fa5b98417afc6 Mon Sep 17 00:00:00 2001
From: Jan Huwald <jh@sotun.de>
Date: Tue, 4 Jun 2013 12:08:48 +0200
Subject: packed_array: add a little atomic access logic


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;
     }
 
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