1/* sem_wait -- wait on a semaphore. Generic futex-using version.
2 Copyright (C) 2003-2021 Free Software Foundation, Inc.
3 This file is part of the GNU C Library.
4 Contributed by Paul Mackerras <paulus@au.ibm.com>, 2003.
5
6 The GNU C Library is free software; you can redistribute it and/or
7 modify it under the terms of the GNU Lesser General Public
8 License as published by the Free Software Foundation; either
9 version 2.1 of the License, or (at your option) any later version.
10
11 The GNU C Library is distributed in the hope that it will be useful,
12 but WITHOUT ANY WARRANTY; without even the implied warranty of
13 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
14 Lesser General Public License for more details.
15
16 You should have received a copy of the GNU Lesser General Public
17 License along with the GNU C Library; if not, see
18 <https://www.gnu.org/licenses/>. */
19
20#include <lowlevellock.h> /* lll_futex* used by the old code. */
21#include "semaphoreP.h"
22#include "sem_waitcommon.c"
23
24int
25__new_sem_wait (sem_t *sem)
26{
27 /* We need to check whether we need to act upon a cancellation request here
28 because POSIX specifies that cancellation points "shall occur" in
29 sem_wait and sem_timedwait, which also means that they need to check
30 this regardless whether they block or not (unlike "may occur"
31 functions). See the POSIX Rationale for this requirement: Section
32 "Thread Cancellation Overview" [1] and austin group issue #1076 [2]
33 for thoughs on why this may be a suboptimal design.
34
35 [1] http://pubs.opengroup.org/onlinepubs/9699919799/xrat/V4_xsh_chap02.html
36 [2] http://austingroupbugs.net/view.php?id=1076 for thoughts on why this
37 */
38 __pthread_testcancel ();
39
40 if (__new_sem_wait_fast ((struct new_sem *) sem, 0) == 0)
41 return 0;
42 else
43 return __new_sem_wait_slow64 ((struct new_sem *) sem,
44 CLOCK_REALTIME, NULL);
45}
46versioned_symbol (libpthread, __new_sem_wait, sem_wait, GLIBC_2_1);
47
48#if SHLIB_COMPAT (libpthread, GLIBC_2_0, GLIBC_2_1)
49int
50attribute_compat_text_section
51__old_sem_wait (sem_t *sem)
52{
53 int *futex = (int *) sem;
54 int err;
55
56 do
57 {
58 if (atomic_decrement_if_positive (futex) > 0)
59 return 0;
60
61 /* Always assume the semaphore is shared. */
62 err = lll_futex_wait_cancel (futex, 0, LLL_SHARED);
63 }
64 while (err == 0 || err == -EWOULDBLOCK);
65
66 __set_errno (-err);
67 return -1;
68}
69
70compat_symbol (libpthread, __old_sem_wait, sem_wait, GLIBC_2_0);
71#endif
72
73int
74__new_sem_trywait (sem_t *sem)
75{
76 /* We must not fail spuriously, so require a definitive result even if this
77 may lead to a long execution time. */
78 if (__new_sem_wait_fast ((struct new_sem *) sem, 1) == 0)
79 return 0;
80 __set_errno (EAGAIN);
81 return -1;
82}
83versioned_symbol (libpthread, __new_sem_trywait, sem_trywait, GLIBC_2_1);
84#if SHLIB_COMPAT (libpthread, GLIBC_2_0, GLIBC_2_1)
85int
86__old_sem_trywait (sem_t *sem)
87{
88 int *futex = (int *) sem;
89 int val;
90
91 if (*futex > 0)
92 {
93 val = atomic_decrement_if_positive (futex);
94 if (val > 0)
95 return 0;
96 }
97
98 __set_errno (EAGAIN);
99 return -1;
100}
101compat_symbol (libpthread, __old_sem_trywait, sem_trywait, GLIBC_2_0);
102#endif
103