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/* Copyright (C) 2002-2017 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 (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. */
rwlock->__data.__shared = (iattr->pshared == PTHREAD_PROCESS_PRIVATE
? 0 : FUTEX_PRIVATE_FLAG);
return 0;
}
strong_alias (__pthread_rwlock_init, pthread_rwlock_init)
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