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74 lines
2.6 KiB
C
74 lines
2.6 KiB
C
/* Copyright (C) 2002,2007,2009,2011 Free Software Foundation, Inc.
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This file is part of the GNU C Library.
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Contributed by Ulrich Drepper <drepper@redhat.com>, 2002.
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The GNU C Library is free software; you can redistribute it and/or
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modify it under the terms of the GNU Lesser General Public
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License as published by the Free Software Foundation; either
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version 2.1 of the License, or (at your option) any later version.
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The GNU C Library is distributed in the hope that it will be useful,
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but WITHOUT ANY WARRANTY; without even the implied warranty of
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MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
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Lesser General Public License for more details.
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You should have received a copy of the GNU Lesser General Public
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License along with the GNU C Library; if not, see
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<http://www.gnu.org/licenses/>. */
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#include "pthreadP.h"
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#include <string.h>
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#include <kernel-features.h>
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static const struct pthread_rwlockattr default_attr =
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{
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.lockkind = PTHREAD_RWLOCK_DEFAULT_NP,
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.pshared = PTHREAD_PROCESS_PRIVATE
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};
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int
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__pthread_rwlock_init (rwlock, attr)
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pthread_rwlock_t *rwlock;
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const pthread_rwlockattr_t *attr;
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{
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const struct pthread_rwlockattr *iattr;
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iattr = ((const struct pthread_rwlockattr *) attr) ?: &default_attr;
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memset (rwlock, '\0', sizeof (*rwlock));
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rwlock->__data.__flags
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= iattr->lockkind == PTHREAD_RWLOCK_PREFER_WRITER_NONRECURSIVE_NP;
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/* The __SHARED field is computed to minimize the work that needs to
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be done while handling the futex. There are two inputs: the
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availability of private futexes and whether the rwlock is shared
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or private. Unfortunately the value of a private rwlock is
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fixed: it must be zero. The PRIVATE_FUTEX flag has the value
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0x80 in case private futexes are available and zero otherwise.
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This leads to the following table:
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| pshared | result
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| shared private | shared private |
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------------+-----------------+-----------------+
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!avail 0 | 0 0 | 0 0 |
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avail 0x80 | 0x80 0 | 0 0x80 |
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If the pshared value is in locking functions XORed with avail
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we get the expected result. */
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#ifdef __ASSUME_PRIVATE_FUTEX
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rwlock->__data.__shared = (iattr->pshared == PTHREAD_PROCESS_PRIVATE
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? 0 : FUTEX_PRIVATE_FLAG);
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#else
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rwlock->__data.__shared = (iattr->pshared == PTHREAD_PROCESS_PRIVATE
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? 0
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: THREAD_GETMEM (THREAD_SELF,
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header.private_futex));
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#endif
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return 0;
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}
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strong_alias (__pthread_rwlock_init, pthread_rwlock_init)
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