138 lines
3.9 KiB
C
138 lines
3.9 KiB
C
/* Copyright (C) 2003, 2004, 2007 Free Software Foundation, Inc.
|
|
This file is part of the GNU C Library.
|
|
Contributed by Martin Schwidefsky <schwidefsky@de.ibm.com>, 2003.
|
|
|
|
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 <errno.h>
|
|
#include <sysdep.h>
|
|
#include <lowlevellock.h>
|
|
#include <pthread.h>
|
|
#include <pthreadP.h>
|
|
|
|
|
|
/* Try to acquire read lock for RWLOCK or return after specfied time. */
|
|
int
|
|
pthread_rwlock_timedrdlock (rwlock, abstime)
|
|
pthread_rwlock_t *rwlock;
|
|
const struct timespec *abstime;
|
|
{
|
|
int result = 0;
|
|
|
|
/* Make sure we are along. */
|
|
lll_mutex_lock(rwlock->__data.__lock);
|
|
|
|
while (1)
|
|
{
|
|
int err;
|
|
|
|
/* Get the rwlock if there is no writer... */
|
|
if (rwlock->__data.__writer == 0
|
|
/* ...and if either no writer is waiting or we prefer readers. */
|
|
&& (!rwlock->__data.__nr_writers_queued
|
|
|| PTHREAD_RWLOCK_PREFER_READER_P (rwlock)))
|
|
{
|
|
/* Increment the reader counter. Avoid overflow. */
|
|
if (++rwlock->__data.__nr_readers == 0)
|
|
{
|
|
/* Overflow on number of readers. */
|
|
--rwlock->__data.__nr_readers;
|
|
result = EAGAIN;
|
|
}
|
|
|
|
break;
|
|
}
|
|
|
|
/* Make sure we are not holding the rwlock as a writer. This is
|
|
a deadlock situation we recognize and report. */
|
|
if (__builtin_expect (rwlock->__data.__writer
|
|
== THREAD_GETMEM (THREAD_SELF, tid), 0))
|
|
{
|
|
result = EDEADLK;
|
|
break;
|
|
}
|
|
|
|
/* Make sure the passed in timeout value is valid. Ideally this
|
|
test would be executed once. But since it must not be
|
|
performed if we would not block at all simply moving the test
|
|
to the front is no option. Replicating all the code is
|
|
costly while this test is not. */
|
|
if (__builtin_expect (abstime->tv_nsec >= 1000000000
|
|
|| abstime->tv_nsec < 0, 0))
|
|
{
|
|
result = EINVAL;
|
|
break;
|
|
}
|
|
|
|
/* Get the current time. So far we support only one clock. */
|
|
struct timeval tv;
|
|
(void) gettimeofday (&tv, NULL);
|
|
|
|
/* Convert the absolute timeout value to a relative timeout. */
|
|
struct timespec rt;
|
|
rt.tv_sec = abstime->tv_sec - tv.tv_sec;
|
|
rt.tv_nsec = abstime->tv_nsec - tv.tv_usec * 1000;
|
|
if (rt.tv_nsec < 0)
|
|
{
|
|
rt.tv_nsec += 1000000000;
|
|
--rt.tv_sec;
|
|
}
|
|
/* Did we already time out? */
|
|
if (rt.tv_sec < 0)
|
|
{
|
|
/* Yep, return with an appropriate error. */
|
|
result = ETIMEDOUT;
|
|
break;
|
|
}
|
|
|
|
/* Remember that we are a reader. */
|
|
if (++rwlock->__data.__nr_readers_queued == 0)
|
|
{
|
|
/* Overflow on number of queued readers. */
|
|
--rwlock->__data.__nr_readers_queued;
|
|
result = EAGAIN;
|
|
break;
|
|
}
|
|
|
|
int waitval = rwlock->__data.__readers_wakeup;
|
|
|
|
/* Free the lock. */
|
|
lll_mutex_unlock (rwlock->__data.__lock);
|
|
|
|
/* Wait for the writer to finish. */
|
|
err = lll_futex_timed_wait (&rwlock->__data.__readers_wakeup,
|
|
waitval, &rt);
|
|
|
|
/* Get the lock. */
|
|
lll_mutex_lock (rwlock->__data.__lock);
|
|
|
|
--rwlock->__data.__nr_readers_queued;
|
|
|
|
/* Did the futex call time out? */
|
|
if (err == -ETIMEDOUT)
|
|
{
|
|
/* Yep, report it. */
|
|
result = ETIMEDOUT;
|
|
break;
|
|
}
|
|
}
|
|
|
|
/* We are done, free the lock. */
|
|
lll_mutex_unlock (rwlock->__data.__lock);
|
|
|
|
return result;
|
|
}
|