refcount_c11.c revision 53b272a2813a0b11f107d77100ff8805ada8fbd2 
1/* Copyright (c) 2015, Google Inc.
2 *
3 * Permission to use, copy, modify, and/or distribute this software for any
4 * purpose with or without fee is hereby granted, provided that the above
5 * copyright notice and this permission notice appear in all copies.
6 *
7 * THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
8 * WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
9 * MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY
10 * SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
11 * WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN ACTION
12 * OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF OR IN
13 * CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE. */
14
15#include "internal.h"
16
17
18#if defined(OPENSSL_C11_ATOMIC)
19
20#include <assert.h>
21#include <stdalign.h>
22#include <stdatomic.h>
23#include <stdlib.h>
24
25#include <openssl/type_check.h>
26
27
28/* See comment above the typedef of CRYPTO_refcount_t about these tests. */
29static_assert(alignof(CRYPTO_refcount_t) == alignof(_Atomic CRYPTO_refcount_t),
30              "_Atomic alters the needed alignment of a reference count");
31static_assert(sizeof(CRYPTO_refcount_t) == sizeof(_Atomic CRYPTO_refcount_t),
32              "_Atomic alters the size of a reference count");
33
34static_assert((CRYPTO_refcount_t)-1 == CRYPTO_REFCOUNT_MAX,
35              "CRYPTO_REFCOUNT_MAX is incorrect");
36
37void CRYPTO_refcount_inc(CRYPTO_refcount_t *in_count) {
38  _Atomic CRYPTO_refcount_t *count = (_Atomic CRYPTO_refcount_t *) in_count;
39  uint32_t expected = atomic_load(count);
40
41  while (expected != CRYPTO_REFCOUNT_MAX) {
42    uint32_t new_value = expected + 1;
43    if (atomic_compare_exchange_weak(count, &expected, new_value)) {
44      break;
45    }
46  }
47}
48
49int CRYPTO_refcount_dec_and_test_zero(CRYPTO_refcount_t *in_count) {
50  _Atomic CRYPTO_refcount_t *count = (_Atomic CRYPTO_refcount_t *)in_count;
51  uint32_t expected = atomic_load(count);
52
53  for (;;) {
54    if (expected == 0) {
55      abort();
56    } else if (expected == CRYPTO_REFCOUNT_MAX) {
57      return 0;
58    } else {
59      const uint32_t new_value = expected - 1;
60      if (atomic_compare_exchange_weak(count, &expected, new_value)) {
61        return new_value == 0;
62      }
63    }
64  }
65}
66
67#endif  /* OPENSSL_C11_ATOMIC */
68