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.
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.
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.
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/>. */
20 #include <lowlevellock.h> /* lll_futex* used by the old code. */
21 #include "semaphoreP.h"
22 #include "sem_waitcommon.c"
25 __new_sem_wait (sem_t
*sem
)
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.
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
38 __pthread_testcancel ();
40 if (__new_sem_wait_fast ((struct new_sem
*) sem
, 0) == 0)
43 return __new_sem_wait_slow64 ((struct new_sem
*) sem
,
44 CLOCK_REALTIME
, NULL
);
46 versioned_symbol (libc
, __new_sem_wait
, sem_wait
, GLIBC_2_34
);
48 #if OTHER_SHLIB_COMPAT (libpthread, GLIBC_2_1, GLIBC_2_34)
49 compat_symbol (libpthread
, __new_sem_wait
, sem_wait
, GLIBC_2_1
);
52 #if OTHER_SHLIB_COMPAT (libpthread, GLIBC_2_0, GLIBC_2_1)
54 attribute_compat_text_section
55 __old_sem_wait (sem_t
*sem
)
57 int *futex
= (int *) sem
;
62 if (atomic_decrement_if_positive (futex
) > 0)
65 /* Always assume the semaphore is shared. */
66 err
= lll_futex_wait_cancel (futex
, 0, LLL_SHARED
);
68 while (err
== 0 || err
== -EWOULDBLOCK
);
74 compat_symbol (libpthread
, __old_sem_wait
, sem_wait
, GLIBC_2_0
);
78 __new_sem_trywait (sem_t
*sem
)
80 /* We must not fail spuriously, so require a definitive result even if this
81 may lead to a long execution time. */
82 if (__new_sem_wait_fast ((struct new_sem
*) sem
, 1) == 0)
87 versioned_symbol (libc
, __new_sem_trywait
, sem_trywait
, GLIBC_2_34
);
89 #if OTHER_SHLIB_COMPAT (libpthread, GLIBC_2_1, GLIBC_2_34)
90 compat_symbol (libpthread
, __new_sem_trywait
, sem_trywait
, GLIBC_2_1
);
93 #if OTHER_SHLIB_COMPAT (libpthread, GLIBC_2_0, GLIBC_2_1)
95 __old_sem_trywait (sem_t
*sem
)
97 int *futex
= (int *) sem
;
102 val
= atomic_decrement_if_positive (futex
);
107 __set_errno (EAGAIN
);
110 compat_symbol (libpthread
, __old_sem_trywait
, sem_trywait
, GLIBC_2_0
);