Add negative test case for CompareAndSwap.

base/atomicops_unittest.cc

 // Copyright (c) 2011 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "base/atomicops.h"
 
 #include <stdint.h>
 #include <string.h>
 
 #include "testing/gtest/include/gtest/gtest.h"
@@ skipping 71 matching lines @@
 #define NUM_BITS(T) (sizeof(T) * 8)
 
 
 template <class AtomicType>
 static void TestCompareAndSwap() {
   AtomicType value = 0;
   AtomicType prev = base::subtle::NoBarrier_CompareAndSwap(&value, 0, 1);
   EXPECT_EQ(1, value);
   EXPECT_EQ(0, prev);
 
+  // Verify that CAS will *not* change "value" if it doesn't match the
+  // expected  number.  CAS will always return the actual value of the

[Alexander Potapenko, 2015/11/02 23:06:43]

Please remove the double space.

[bcwhite, 2015/11/03 15:11:36]

Done.  (As I said in our other review...  It's simply *not possible* for me to
type single spaces after periods. :-D)

+  // variable from before any change.
+  AtomicType fail = base::subtle::NoBarrier_CompareAndSwap(&value, 0, 2);
+  EXPECT_EQ(1, value);
+  EXPECT_EQ(1, fail);
+
   // Use test value that has non-zero bits in both halves, more for testing
   // 64-bit implementation on 32-bit platforms.
   const AtomicType k_test_val = (static_cast<uint64_t>(1) <<
                                  (NUM_BITS(AtomicType) - 2)) + 11;
   value = k_test_val;
   prev = base::subtle::NoBarrier_CompareAndSwap(&value, 0, 5);
   EXPECT_EQ(k_test_val, value);
   EXPECT_EQ(k_test_val, prev);
 
   value = k_test_val;
@@ skipping 130 matching lines @@
 
 TEST(AtomicOpsTest, Store) {
   TestStore<base::subtle::Atomic32>();
   TestStore<base::subtle::AtomicWord>();
 }
 
 TEST(AtomicOpsTest, Load) {
   TestLoad<base::subtle::Atomic32>();
   TestLoad<base::subtle::AtomicWord>();
 }