1 | /* sem_wait -- wait on a semaphore. Generic futex-using version. |
2 | Copyright (C) 2003-2019 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 | <http://www.gnu.org/licenses/>. */ |
19 | |
20 | #include <lowlevellock.h> /* lll_futex* used by the old code. */ |
21 | #include "sem_waitcommon.c" |
22 | |
23 | int |
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 | } |
45 | versioned_symbol (libpthread, __new_sem_wait, sem_wait, GLIBC_2_1); |
46 | |
47 | #if SHLIB_COMPAT (libpthread, GLIBC_2_0, GLIBC_2_1) |
48 | int |
49 | attribute_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 | |
69 | compat_symbol (libpthread, __old_sem_wait, sem_wait, GLIBC_2_0); |
70 | #endif |
71 | |
72 | int |
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 | } |
82 | versioned_symbol (libpthread, __new_sem_trywait, sem_trywait, GLIBC_2_1); |
83 | #if SHLIB_COMPAT (libpthread, GLIBC_2_0, GLIBC_2_1) |
84 | int |
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 | } |
100 | compat_symbol (libpthread, __old_sem_trywait, sem_trywait, GLIBC_2_0); |
101 | #endif |
102 | |