| /* Copyright (C) 2002-2014 Free Software Foundation, Inc. |
| This file is part of the GNU C Library. |
| Contributed by Ulrich Drepper <drepper@redhat.com>, 2002. |
| |
| The GNU C Library is free software; you can redistribute it and/or |
| modify it under the terms of the GNU Lesser General Public |
| License as published by the Free Software Foundation; either |
| version 2.1 of the License, or (at your option) any later version. |
| |
| The GNU C Library is distributed in the hope that it will be useful, |
| but WITHOUT ANY WARRANTY; without even the implied warranty of |
| MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU |
| Lesser General Public License for more details. |
| |
| You should have received a copy of the GNU Lesser General Public |
| License along with the GNU C Library; if not, see |
| <http://www.gnu.org/licenses/>. */ |
| |
| #include "pthreadP.h" |
| #include <string.h> |
| #include <kernel-features.h> |
| |
| |
| static const struct pthread_rwlockattr default_rwlockattr = |
| { |
| .lockkind = PTHREAD_RWLOCK_DEFAULT_NP, |
| .pshared = PTHREAD_PROCESS_PRIVATE |
| }; |
| |
| |
| int |
| __pthread_rwlock_init (rwlock, attr) |
| pthread_rwlock_t *rwlock; |
| const pthread_rwlockattr_t *attr; |
| { |
| const struct pthread_rwlockattr *iattr; |
| |
| iattr = ((const struct pthread_rwlockattr *) attr) ?: &default_rwlockattr; |
| |
| memset (rwlock, '\0', sizeof (*rwlock)); |
| |
| rwlock->__data.__flags |
| = iattr->lockkind == PTHREAD_RWLOCK_PREFER_WRITER_NONRECURSIVE_NP; |
| |
| /* The __SHARED field is computed to minimize the work that needs to |
| be done while handling the futex. There are two inputs: the |
| availability of private futexes and whether the rwlock is shared |
| or private. Unfortunately the value of a private rwlock is |
| fixed: it must be zero. The PRIVATE_FUTEX flag has the value |
| 0x80 in case private futexes are available and zero otherwise. |
| This leads to the following table: |
| |
| | pshared | result |
| | shared private | shared private | |
| ------------+-----------------+-----------------+ |
| !avail 0 | 0 0 | 0 0 | |
| avail 0x80 | 0x80 0 | 0 0x80 | |
| |
| If the pshared value is in locking functions XORed with avail |
| we get the expected result. */ |
| #ifdef __ASSUME_PRIVATE_FUTEX |
| rwlock->__data.__shared = (iattr->pshared == PTHREAD_PROCESS_PRIVATE |
| ? 0 : FUTEX_PRIVATE_FLAG); |
| #else |
| rwlock->__data.__shared = (iattr->pshared == PTHREAD_PROCESS_PRIVATE |
| ? 0 |
| : THREAD_GETMEM (THREAD_SELF, |
| header.private_futex)); |
| #endif |
| |
| return 0; |
| } |
| strong_alias (__pthread_rwlock_init, pthread_rwlock_init) |
