diff options
Diffstat (limited to 'libpthread/nptl/pthread_rwlock_init.c')
-rw-r--r-- | libpthread/nptl/pthread_rwlock_init.c | 73 |
1 files changed, 73 insertions, 0 deletions
diff --git a/libpthread/nptl/pthread_rwlock_init.c b/libpthread/nptl/pthread_rwlock_init.c new file mode 100644 index 000000000..aab832eea --- /dev/null +++ b/libpthread/nptl/pthread_rwlock_init.c @@ -0,0 +1,73 @@ +/* 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, write to the Free + Software Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA + 02111-1307 USA. */ + +#include "pthreadP.h" +#include <bits/kernel-features.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) |