-/* Copyright (C) 2002 Free Software Foundation, Inc.
+/* 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.
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. */
+ 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 =
{
iattr = ((const struct pthread_rwlockattr *) attr) ?: &default_attr;
- rwlock->__data.__lock = 0;
+ memset (rwlock, '\0', sizeof (*rwlock));
+
rwlock->__data.__flags
= iattr->lockkind == PTHREAD_RWLOCK_PREFER_WRITER_NONRECURSIVE_NP;
- rwlock->__data.__nr_readers = 0;
- rwlock->__data.__writer = 0;
- rwlock->__data.__readers_wakeup = 0;
- rwlock->__data.__writer_wakeup = 0;
- rwlock->__data.__nr_readers_queued = 0;
- rwlock->__data.__nr_writers_queued = 0;
+
+ /* 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;
}