mirror of git://sourceware.org/git/glibc.git
121 lines
3.4 KiB
C
121 lines
3.4 KiB
C
/* Acquire a rwlock for reading. Generic version.
|
|
Copyright (C) 2002-2018 Free Software Foundation, Inc.
|
|
This file is part of the GNU C Library.
|
|
|
|
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 <pthread.h>
|
|
#include <assert.h>
|
|
|
|
#include <pt-internal.h>
|
|
|
|
/* Acquire the rwlock *RWLOCK for reading blocking until *ABSTIME if
|
|
it is already held. As a GNU extension, if TIMESPEC is NULL then
|
|
wait forever. */
|
|
int
|
|
__pthread_rwlock_timedrdlock_internal (struct __pthread_rwlock *rwlock,
|
|
const struct timespec *abstime)
|
|
{
|
|
error_t err;
|
|
int drain;
|
|
struct __pthread *self;
|
|
|
|
__pthread_spin_lock (&rwlock->__lock);
|
|
if (__pthread_spin_trylock (&rwlock->__held) == 0)
|
|
/* Successfully acquired the lock. */
|
|
{
|
|
assert (rwlock->__readerqueue == 0);
|
|
assert (rwlock->__writerqueue == 0);
|
|
assert (rwlock->__readers == 0);
|
|
|
|
rwlock->__readers = 1;
|
|
__pthread_spin_unlock (&rwlock->__lock);
|
|
return 0;
|
|
}
|
|
else
|
|
/* Lock is held, but is held by a reader? */
|
|
if (rwlock->__readers > 0)
|
|
/* Just add ourself to number of readers. */
|
|
{
|
|
assert (rwlock->__readerqueue == 0);
|
|
rwlock->__readers++;
|
|
__pthread_spin_unlock (&rwlock->__lock);
|
|
return 0;
|
|
}
|
|
|
|
/* The lock is busy. */
|
|
|
|
/* Better be blocked by a writer. */
|
|
assert (rwlock->__readers == 0);
|
|
|
|
if (abstime != NULL && (abstime->tv_nsec < 0 || abstime->tv_nsec >= 1000000000))
|
|
return EINVAL;
|
|
|
|
self = _pthread_self ();
|
|
|
|
/* Add ourself to the queue. */
|
|
__pthread_enqueue (&rwlock->__readerqueue, self);
|
|
__pthread_spin_unlock (&rwlock->__lock);
|
|
|
|
/* Block the thread. */
|
|
if (abstime != NULL)
|
|
err = __pthread_timedblock (self, abstime, CLOCK_REALTIME);
|
|
else
|
|
{
|
|
err = 0;
|
|
__pthread_block (self);
|
|
}
|
|
|
|
__pthread_spin_lock (&rwlock->__lock);
|
|
if (self->prevp == NULL)
|
|
/* Another thread removed us from the queue, which means a wakeup message
|
|
has been sent. It was either consumed while we were blocking, or
|
|
queued after we timed out and before we acquired the rwlock lock, in
|
|
which case the message queue must be drained. */
|
|
drain = err ? 1 : 0;
|
|
else
|
|
{
|
|
/* We're still in the queue. Noone attempted to wake us up, i.e. we
|
|
timed out. */
|
|
__pthread_dequeue (self);
|
|
drain = 0;
|
|
}
|
|
__pthread_spin_unlock (&rwlock->__lock);
|
|
|
|
if (drain)
|
|
__pthread_block (self);
|
|
|
|
if (err)
|
|
{
|
|
assert (err == ETIMEDOUT);
|
|
return err;
|
|
}
|
|
|
|
/* The reader count has already been increment by whoever woke us
|
|
up. */
|
|
|
|
assert (rwlock->__readers > 0);
|
|
|
|
return 0;
|
|
}
|
|
|
|
int
|
|
__pthread_rwlock_timedrdlock (struct __pthread_rwlock *rwlock,
|
|
const struct timespec *abstime)
|
|
{
|
|
return __pthread_rwlock_timedrdlock_internal (rwlock, abstime);
|
|
}
|
|
weak_alias (__pthread_rwlock_timedrdlock, pthread_rwlock_timedrdlock)
|