1 /* Copyright (C) 2002, 2007, 2009 Free Software Foundation, Inc.
2 This file is part of the GNU C Library.
3 Contributed by Ulrich Drepper <drepper@redhat.com>, 2002.
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 <http://www.gnu.org/licenses/>. */
18
19 #include "pthreadP.h"
20 #include <bits/kernel-features.h>
21 #include <string.h>
22
23 static const struct pthread_rwlockattr default_attr =
24 {
25 .lockkind = PTHREAD_RWLOCK_DEFAULT_NP,
26 .pshared = PTHREAD_PROCESS_PRIVATE
27 };
28
29
30 int
__pthread_rwlock_init(pthread_rwlock_t * rwlock,const pthread_rwlockattr_t * attr)31 __pthread_rwlock_init (
32 pthread_rwlock_t *rwlock,
33 const pthread_rwlockattr_t *attr)
34 {
35 const struct pthread_rwlockattr *iattr;
36
37 iattr = ((const struct pthread_rwlockattr *) attr) ?: &default_attr;
38
39 memset (rwlock, '\0', sizeof (*rwlock));
40
41 rwlock->__data.__flags
42 = iattr->lockkind == PTHREAD_RWLOCK_PREFER_WRITER_NONRECURSIVE_NP;
43
44 /* The __SHARED field is computed to minimize the work that needs to
45 be done while handling the futex. There are two inputs: the
46 availability of private futexes and whether the rwlock is shared
47 or private. Unfortunately the value of a private rwlock is
48 fixed: it must be zero. The PRIVATE_FUTEX flag has the value
49 0x80 in case private futexes are available and zero otherwise.
50 This leads to the following table:
51
52 | pshared | result
53 | shared private | shared private |
54 ------------+-----------------+-----------------+
55 !avail 0 | 0 0 | 0 0 |
56 avail 0x80 | 0x80 0 | 0 0x80 |
57
58 If the pshared value is in locking functions XORed with avail
59 we get the expected result. */
60 #ifdef __ASSUME_PRIVATE_FUTEX
61 rwlock->__data.__shared = (iattr->pshared == PTHREAD_PROCESS_PRIVATE
62 ? 0 : FUTEX_PRIVATE_FLAG);
63 #else
64 rwlock->__data.__shared = (iattr->pshared == PTHREAD_PROCESS_PRIVATE
65 ? 0
66 : THREAD_GETMEM (THREAD_SELF,
67 header.private_futex));
68 #endif
69
70 return 0;
71 }
72 strong_alias (__pthread_rwlock_init, pthread_rwlock_init)
73