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/* Copyright (C) 2002, 2007, 2009 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 <bits/kernel-features.h> #include <string.h> static const struct pthread_rwlockattr default_attr = { .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_attr; 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) |