1/* sem_wait -- wait on a semaphore. Generic futex-using version.
2 Copyright (C) 2003-2020 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 "sem_waitcommon.c"
22
23int
24__new_sem_wait (sem_t *sem)
25{
26 /* We need to check whether we need to act upon a cancellation request here
27 because POSIX specifies that cancellation points "shall occur" in
28 sem_wait and sem_timedwait, which also means that they need to check
29 this regardless whether they block or not (unlike "may occur"
30 functions). See the POSIX Rationale for this requirement: Section
31 "Thread Cancellation Overview" [1] and austin group issue #1076 [2]
32 for thoughs on why this may be a suboptimal design.
33
34 [1] http://pubs.opengroup.org/onlinepubs/9699919799/xrat/V4_xsh_chap02.html
35 [2] http://austingroupbugs.net/view.php?id=1076 for thoughts on why this
36 */
37 __pthread_testcancel ();
38
39 if (__new_sem_wait_fast ((struct new_sem *) sem, 0) == 0)
40 return 0;
41 else
42 return __new_sem_wait_slow ((struct new_sem *) sem,
43 CLOCK_REALTIME, NULL);
44}
45versioned_symbol (libpthread, __new_sem_wait, sem_wait, GLIBC_2_1);
46
47#if SHLIB_COMPAT (libpthread, GLIBC_2_0, GLIBC_2_1)
48int
49attribute_compat_text_section
50__old_sem_wait (sem_t *sem)
51{
52 int *futex = (int *) sem;
53 int err;
54
55 do
56 {
57 if (atomic_decrement_if_positive (futex) > 0)
58 return 0;
59
60 /* Always assume the semaphore is shared. */
61 err = lll_futex_wait_cancel (futex, 0, LLL_SHARED);
62 }
63 while (err == 0 || err == -EWOULDBLOCK);
64
65 __set_errno (-err);
66 return -1;
67}
68
69compat_symbol (libpthread, __old_sem_wait, sem_wait, GLIBC_2_0);
70#endif
71
72int
73__new_sem_trywait (sem_t *sem)
74{
75 /* We must not fail spuriously, so require a definitive result even if this
76 may lead to a long execution time. */
77 if (__new_sem_wait_fast ((struct new_sem *) sem, 1) == 0)
78 return 0;
79 __set_errno (EAGAIN);
80 return -1;
81}
82versioned_symbol (libpthread, __new_sem_trywait, sem_trywait, GLIBC_2_1);
83#if SHLIB_COMPAT (libpthread, GLIBC_2_0, GLIBC_2_1)
84int
85__old_sem_trywait (sem_t *sem)
86{
87 int *futex = (int *) sem;
88 int val;
89
90 if (*futex > 0)
91 {
92 val = atomic_decrement_if_positive (futex);
93 if (val > 0)
94 return 0;
95 }
96
97 __set_errno (EAGAIN);
98 return -1;
99}
100compat_symbol (libpthread, __old_sem_trywait, sem_trywait, GLIBC_2_0);
101#endif
102