1 /* Lock a semaphore if it does not require blocking. Generic version.
2 Copyright (C) 2005-2021 Free Software Foundation, Inc.
3 This file is part of the GNU C Library.
4
5 The GNU C Library is free software; you can redistribute it and/or
6 modify it under the terms of the GNU Lesser General Public
7 License as published by the Free Software Foundation; either
8 version 2.1 of the License, or (at your option) any later version.
9
10 The GNU C Library is distributed in the hope that it will be useful,
11 but WITHOUT ANY WARRANTY; without even the implied warranty of
12 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
13 Lesser General Public License for more details.
14
15 You should have received a copy of the GNU Lesser General Public
16 License along with the GNU C Library; if not, see
17 <https://www.gnu.org/licenses/>. */
18
19 #include <semaphore.h>
20 #include <errno.h>
21
22 #include <pt-internal.h>
23
24 int
__sem_waitfast(struct new_sem * isem,int definitive_result)25 __sem_waitfast (struct new_sem *isem, int definitive_result)
26 {
27 #if __HAVE_64B_ATOMICS
28 uint64_t d = atomic_load_relaxed (&isem->data);
29
30 do
31 {
32 if ((d & SEM_VALUE_MASK) == 0)
33 break;
34 if (atomic_compare_exchange_weak_acquire (&isem->data, &d, d - 1))
35 /* Successful down. */
36 return 0;
37 }
38 while (definitive_result);
39 return -1;
40 #else
41 unsigned v = atomic_load_relaxed (&isem->value);
42
43 do
44 {
45 if ((v >> SEM_VALUE_SHIFT) == 0)
46 break;
47 if (atomic_compare_exchange_weak_acquire (&isem->value,
48 &v, v - (1 << SEM_VALUE_SHIFT)))
49 /* Successful down. */
50 return 0;
51 }
52 while (definitive_result);
53 return -1;
54 #endif
55 }
56