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.
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 (libpthread
, __new_sem_wait
, sem_wait
, GLIBC_2_1
);
48 #if SHLIB_COMPAT (libpthread, GLIBC_2_0, GLIBC_2_1)
50 attribute_compat_text_section
51 __old_sem_wait (sem_t
*sem
)
53 int *futex
= (int *) sem
;
58 if (atomic_decrement_if_positive (futex
) > 0)
61 /* Always assume the semaphore is shared. */
62 err
= lll_futex_wait_cancel (futex
, 0, LLL_SHARED
);
64 while (err
== 0 || err
== -EWOULDBLOCK
);
70 compat_symbol (libpthread
, __old_sem_wait
, sem_wait
, GLIBC_2_0
);
74 __new_sem_trywait (sem_t
*sem
)
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)
83 versioned_symbol (libpthread
, __new_sem_trywait
, sem_trywait
, GLIBC_2_1
);
84 #if SHLIB_COMPAT (libpthread, GLIBC_2_0, GLIBC_2_1)
86 __old_sem_trywait (sem_t
*sem
)
88 int *futex
= (int *) sem
;
93 val
= atomic_decrement_if_positive (futex
);
101 compat_symbol (libpthread
, __old_sem_trywait
, sem_trywait
, GLIBC_2_0
);