1 /*
2 * Copyright (c) 2025 Google LLC
3 *
4 * SPDX-License-Identifier: Apache-2.0
5 */
6
7 #include <atomic>
8 #include <cstdint>
9 #include <zephyr/ztest.h>
10
11 namespace
12 {
13 std::atomic<uint8_t> atomic_u8;
14 std::atomic<uint16_t> atomic_u16;
15 std::atomic<uint32_t> atomic_u32;
16 } // namespace
17
18 /**
19 * @brief This `before` function is run before each test in the suite.
20 *
21 * It ensures that all atomic variables are reset to a known state (0)
22 * so that the tests are independent and repeatable.
23 */
cxx_atomic_before(void * fixture)24 static void cxx_atomic_before(void *fixture)
25 {
26 atomic_u8.store(0);
27 atomic_u16.store(0);
28 atomic_u32.store(0);
29 }
30
31 /**
32 * @brief Tests the 1-byte (uint8_t) atomic implementation.
33 */
ZTEST(cxx_atomic,test_u8_compare_exchange_weak)34 ZTEST(cxx_atomic, test_u8_compare_exchange_weak)
35 {
36 /* === Test 1: Successful exchange === */
37 /* We expect the value to be 0, so this exchange should succeed. */
38 uint8_t expected = 0;
39 const uint8_t desired = 42;
40
41 /* Loop until the weak exchange succeeds. */
42 while (!atomic_u8.compare_exchange_weak(expected, desired)) {
43 }
44 zassert_equal(atomic_u8.load(), desired, "Value should have been updated to 42");
45
46 /* === Test 2: Failed exchange === */
47 /* Now, the atomic value is 42. We will set `expected` to 0, so the exchange must fail. */
48 expected = 0;
49 const uint8_t new_desired = 99;
50 bool success = atomic_u8.compare_exchange_weak(expected, new_desired);
51
52 zassert_false(success, "Exchange should have failed");
53 zassert_equal(atomic_u8.load(), desired, "Value should remain 42");
54 /* Crucially, `expected` should be updated with the value that caused the failure. */
55 zassert_equal(expected, desired, "Expected should be updated to 42");
56 }
57
58 /**
59 * @brief Tests the 2-byte (uint16_t) atomic implementation.
60 */
ZTEST(cxx_atomic,test_u16_compare_exchange_weak)61 ZTEST(cxx_atomic, test_u16_compare_exchange_weak)
62 {
63 /* === Test 1: Successful exchange === */
64 uint16_t expected = 0;
65 const uint16_t desired = 1337;
66 while (!atomic_u16.compare_exchange_weak(expected, desired)) {
67 }
68 zassert_equal(atomic_u16.load(), desired, "Value should have been updated to 1337");
69
70 /* === Test 2: Failed exchange === */
71 expected = 0;
72 const uint16_t new_desired = 9999;
73 bool success = atomic_u16.compare_exchange_weak(expected, new_desired);
74
75 zassert_false(success, "Exchange should have failed");
76 zassert_equal(atomic_u16.load(), desired, "Value should remain 1337");
77 zassert_equal(expected, desired, "Expected should be updated to 1337");
78 }
79
80 /**
81 * @brief Tests the 4-byte (uint32_t) atomic implementation.
82 */
ZTEST(cxx_atomic,test_u32_compare_exchange_weak)83 ZTEST(cxx_atomic, test_u32_compare_exchange_weak)
84 {
85 /* === Test 1: Successful exchange === */
86 uint32_t expected = 0;
87 const uint32_t desired = 0xDEADBEEF;
88 while (!atomic_u32.compare_exchange_weak(expected, desired)) {
89 }
90 zassert_equal(atomic_u32.load(), desired, "Value should have been updated to 0xDEADBEEF");
91
92 /* === Test 2: Failed exchange === */
93 expected = 0;
94 const uint32_t new_desired = 0x12345678;
95 bool success = atomic_u32.compare_exchange_weak(expected, new_desired);
96
97 zassert_false(success, "Exchange should have failed");
98 zassert_equal(atomic_u32.load(), desired, "Value should remain 0xDEADBEEF");
99 zassert_equal(expected, desired, "Expected should be updated to 0xDEADBEEF");
100 }
101
102 ZTEST_SUITE(cxx_atomic, nullptr, nullptr, cxx_atomic_before, nullptr, nullptr);
103
