mirror of
https://sourceware.org/git/glibc.git
synced 2024-11-25 14:30:06 +00:00
b634486d57
This adds wake-ups that would be missing if assuming that for a non-writer-preferring rwlock, if one thread has acquired a rdlock and does not release it, another thread will eventually acquire a rdlock too despite concurrent write lock acquisition attempts. BZ 14958 is about supporting this assumption. Strictly speaking, this isn't a valid test case, but nonetheless worth supporting (see comment 7 of BZ 14958).
72 lines
2.1 KiB
C
72 lines
2.1 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 <errno.h>
|
|
#include "pthreadP.h"
|
|
#include <lowlevellock.h>
|
|
#include <elide.h>
|
|
#include <stdbool.h>
|
|
|
|
|
|
int
|
|
__pthread_rwlock_tryrdlock (pthread_rwlock_t *rwlock)
|
|
{
|
|
int result = EBUSY;
|
|
bool wake = false;
|
|
|
|
if (ELIDE_TRYLOCK (rwlock->__data.__rwelision,
|
|
rwlock->__data.__lock == 0
|
|
&& rwlock->__data.__nr_readers == 0
|
|
&& rwlock->__data.__writer, 0))
|
|
return 0;
|
|
|
|
lll_lock (rwlock->__data.__lock, rwlock->__data.__shared);
|
|
|
|
if (rwlock->__data.__writer == 0
|
|
&& (rwlock->__data.__nr_writers_queued == 0
|
|
|| PTHREAD_RWLOCK_PREFER_READER_P (rwlock)))
|
|
{
|
|
if (__glibc_unlikely (++rwlock->__data.__nr_readers == 0))
|
|
{
|
|
--rwlock->__data.__nr_readers;
|
|
result = EAGAIN;
|
|
}
|
|
else
|
|
{
|
|
result = 0;
|
|
/* See pthread_rwlock_rdlock. */
|
|
if (rwlock->__data.__nr_readers == 1
|
|
&& rwlock->__data.__nr_readers_queued > 0
|
|
&& rwlock->__data.__nr_writers_queued > 0)
|
|
{
|
|
++rwlock->__data.__readers_wakeup;
|
|
wake = true;
|
|
}
|
|
}
|
|
}
|
|
|
|
lll_unlock (rwlock->__data.__lock, rwlock->__data.__shared);
|
|
|
|
if (wake)
|
|
lll_futex_wake (&rwlock->__data.__readers_wakeup, INT_MAX,
|
|
rwlock->__data.__shared);
|
|
|
|
return result;
|
|
}
|
|
strong_alias (__pthread_rwlock_tryrdlock, pthread_rwlock_tryrdlock)
|