1 /* sem_wait -- wait on a semaphore. Generic futex-using version.
2 Copyright (C) 2003-2022 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 <lowlevellock.h> /* lll_futex* used by the old code. */
20 #include "semaphoreP.h"
21 #include "sem_waitcommon.c"
22
23 int
__new_sem_wait(sem_t * sem)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_slow64 ((struct new_sem *) sem,
43 CLOCK_REALTIME, NULL);
44 }
45 versioned_symbol (libc, __new_sem_wait, sem_wait, GLIBC_2_34);
46
47 #if OTHER_SHLIB_COMPAT (libpthread, GLIBC_2_1, GLIBC_2_34)
48 compat_symbol (libpthread, __new_sem_wait, sem_wait, GLIBC_2_1);
49 #endif
50
51 #if OTHER_SHLIB_COMPAT (libpthread, GLIBC_2_0, GLIBC_2_1)
52 int
53 attribute_compat_text_section
__old_sem_wait(sem_t * sem)54 __old_sem_wait (sem_t *sem)
55 {
56 int *futex = (int *) sem;
57 int err;
58
59 do
60 {
61 if (atomic_decrement_if_positive (futex) > 0)
62 return 0;
63
64 /* Always assume the semaphore is shared. */
65 err = lll_futex_wait_cancel (futex, 0, LLL_SHARED);
66 }
67 while (err == 0 || err == -EWOULDBLOCK);
68
69 __set_errno (-err);
70 return -1;
71 }
72
73 compat_symbol (libpthread, __old_sem_wait, sem_wait, GLIBC_2_0);
74 #endif
75
76 int
__new_sem_trywait(sem_t * sem)77 __new_sem_trywait (sem_t *sem)
78 {
79 /* We must not fail spuriously, so require a definitive result even if this
80 may lead to a long execution time. */
81 if (__new_sem_wait_fast ((struct new_sem *) sem, 1) == 0)
82 return 0;
83 __set_errno (EAGAIN);
84 return -1;
85 }
86 versioned_symbol (libc, __new_sem_trywait, sem_trywait, GLIBC_2_34);
87
88 #if OTHER_SHLIB_COMPAT (libpthread, GLIBC_2_1, GLIBC_2_34)
89 compat_symbol (libpthread, __new_sem_trywait, sem_trywait, GLIBC_2_1);
90 #endif
91
92 #if OTHER_SHLIB_COMPAT (libpthread, GLIBC_2_0, GLIBC_2_1)
93 int
__old_sem_trywait(sem_t * sem)94 __old_sem_trywait (sem_t *sem)
95 {
96 int *futex = (int *) sem;
97 int val;
98
99 if (*futex > 0)
100 {
101 val = atomic_decrement_if_positive (futex);
102 if (val > 0)
103 return 0;
104 }
105
106 __set_errno (EAGAIN);
107 return -1;
108 }
109 compat_symbol (libpthread, __old_sem_trywait, sem_trywait, GLIBC_2_0);
110 #endif
111