1 | /* sem_wait -- wait on a semaphore. Generic futex-using version. |
2 | Copyright (C) 2003-2017 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, NULL); |
43 | } |
44 | versioned_symbol (libpthread, __new_sem_wait, sem_wait, GLIBC_2_1); |
45 | |
46 | #if SHLIB_COMPAT (libpthread, GLIBC_2_0, GLIBC_2_1) |
47 | int |
48 | attribute_compat_text_section |
49 | __old_sem_wait (sem_t *sem) |
50 | { |
51 | int *futex = (int *) sem; |
52 | int err; |
53 | |
54 | do |
55 | { |
56 | if (atomic_decrement_if_positive (futex) > 0) |
57 | return 0; |
58 | |
59 | /* Enable asynchronous cancellation. Required by the standard. */ |
60 | int oldtype = __pthread_enable_asynccancel (); |
61 | |
62 | /* Always assume the semaphore is shared. */ |
63 | err = lll_futex_wait (futex, 0, LLL_SHARED); |
64 | |
65 | /* Disable asynchronous cancellation. */ |
66 | __pthread_disable_asynccancel (oldtype); |
67 | } |
68 | while (err == 0 || err == -EWOULDBLOCK); |
69 | |
70 | __set_errno (-err); |
71 | return -1; |
72 | } |
73 | |
74 | compat_symbol (libpthread, __old_sem_wait, sem_wait, GLIBC_2_0); |
75 | #endif |
76 | |
77 | int |
78 | __new_sem_trywait (sem_t *sem) |
79 | { |
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) |
83 | return 0; |
84 | __set_errno (EAGAIN); |
85 | return -1; |
86 | } |
87 | versioned_symbol (libpthread, __new_sem_trywait, sem_trywait, GLIBC_2_1); |
88 | #if SHLIB_COMPAT (libpthread, GLIBC_2_0, GLIBC_2_1) |
89 | int |
90 | __old_sem_trywait (sem_t *sem) |
91 | { |
92 | int *futex = (int *) sem; |
93 | int val; |
94 | |
95 | if (*futex > 0) |
96 | { |
97 | val = atomic_decrement_if_positive (futex); |
98 | if (val > 0) |
99 | return 0; |
100 | } |
101 | |
102 | __set_errno (EAGAIN); |
103 | return -1; |
104 | } |
105 | compat_symbol (libpthread, __old_sem_trywait, sem_trywait, GLIBC_2_0); |
106 | #endif |
107 | |