mirror of
https://sourceware.org/git/glibc.git
synced 2024-11-10 07:10:06 +00:00
a2f0363f81
This adds new functions for futex operations, starting with wait, abstimed_wait, reltimed_wait, wake. They add documentation and error checking according to the current draft of the Linux kernel futex manpage. Waiting with absolute or relative timeouts is split into separate functions. This allows for removing a few cases of code duplication in pthreads code, which uses absolute timeouts; also, it allows us to put platform-specific code to go from an absolute to a relative timeout into the platform-specific futex abstractions.. Futex operations that can be canceled are also split out into separate functions suffixed by "_cancelable". There are separate versions for both Linux and NaCl; while they currently differ only slightly, my expectation is that the separate versions of lowlevellock-futex.h will eventually be merged into futex-internal.h when we get to move the lll_ functions over to the new futex API.
138 lines
4.0 KiB
C
138 lines
4.0 KiB
C
/* Copyright (C) 2003-2015 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, see
|
|
<http://www.gnu.org/licenses/>. */
|
|
|
|
#include <errno.h>
|
|
#include <sysdep.h>
|
|
#include <lowlevellock.h>
|
|
#include <futex-internal.h>
|
|
#include <pthread.h>
|
|
#include <pthreadP.h>
|
|
#include <sys/time.h>
|
|
#include <stdbool.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;
|
|
bool wake = false;
|
|
int futex_shared =
|
|
rwlock->__data.__shared == LLL_PRIVATE ? FUTEX_PRIVATE : FUTEX_SHARED;
|
|
|
|
/* Make sure we are alone. */
|
|
lll_lock(rwlock->__data.__lock, rwlock->__data.__shared);
|
|
|
|
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;
|
|
}
|
|
else
|
|
{
|
|
/* 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;
|
|
}
|
|
}
|
|
|
|
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;
|
|
}
|
|
|
|
/* 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_unlock (rwlock->__data.__lock, rwlock->__data.__shared);
|
|
|
|
/* Wait for the writer to finish. We handle ETIMEDOUT below; on other
|
|
return values, we decide how to continue based on the state of the
|
|
rwlock. */
|
|
err = futex_abstimed_wait (&rwlock->__data.__readers_wakeup, waitval,
|
|
abstime, futex_shared);
|
|
|
|
/* Get the lock. */
|
|
lll_lock (rwlock->__data.__lock, rwlock->__data.__shared);
|
|
|
|
--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_unlock (rwlock->__data.__lock, rwlock->__data.__shared);
|
|
|
|
if (wake)
|
|
futex_wake (&rwlock->__data.__readers_wakeup, INT_MAX, futex_shared);
|
|
|
|
return result;
|
|
}
|