mirror of
https://sourceware.org/git/glibc.git
synced 2024-12-23 11:20:07 +00:00
74 lines
2.6 KiB
C
74 lines
2.6 KiB
C
/* Copyright (C) 2002-2015 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)
|