[userspace-rcu.git] / compat_futex.c

/*
 * compat_futex.c
 *
 * Userspace RCU library - sys_futex compatibility code
 *
 * Copyright (c) 2009 Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
 *
 * This 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.
 *
 * This 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 this library; if not, write to the Free Software
 * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
 */

#include <stdio.h>
#include <pthread.h>
#include <signal.h>
#include <assert.h>
#include <errno.h>
#include <poll.h>
#include <stdint.h>

#include <urcu/arch.h>
#include <urcu/futex.h>
#include <urcu/system.h>

/*
 * Using attribute "weak" for __urcu_compat_futex_lock and
 * __urcu_compat_futex_cond. Those are globally visible by the entire
 * program, even though many shared objects may have their own version.
 * The first version that gets loaded will be used by the entire program
 * (executable and all shared objects).
 */

__attribute__((weak))
pthread_mutex_t __urcu_compat_futex_lock = PTHREAD_MUTEX_INITIALIZER;
__attribute__((weak))
pthread_cond_t __urcu_compat_futex_cond = PTHREAD_COND_INITIALIZER;

/*
 * _NOT SIGNAL-SAFE_. pthread_cond is not signal-safe anyway. Though.
 * For now, timeout, uaddr2 and val3 are unused.
 * Waiter will relinquish the CPU until woken up.
 */

int compat_futex_noasync(int32_t *uaddr, int op, int32_t val,
	const struct timespec *timeout, int32_t *uaddr2, int32_t val3)
{
	int ret;

	/*
	 * Check if NULL. Don't let users expect that they are taken into
	 * account. 
	 */
	assert(!timeout);
	assert(!uaddr2);
	assert(!val3);

	/*
	 * memory barriers to serialize with the previous uaddr modification.
	 */
	cmm_smp_mb();

	ret = pthread_mutex_lock(&__urcu_compat_futex_lock);
	if (ret) {
		errno = ret;
		ret = -1;
		goto end;
	}
	switch (op) {
	case FUTEX_WAIT:
		/*
		 * Wait until *uaddr is changed to something else than "val".
		 * Comparing *uaddr content against val figures out which
		 * thread has been awakened.
		 */
		while (CMM_LOAD_SHARED(*uaddr) == val)
			pthread_cond_wait(&__urcu_compat_futex_cond,
				&__urcu_compat_futex_lock);
		break;
	case FUTEX_WAKE:
		/*
		 * Each wake is sending a broadcast, thus attempting wakeup of
		 * all awaiting threads, independently of their respective
		 * uaddr.
		 */
		pthread_cond_broadcast(&__urcu_compat_futex_cond);
		break;
	default:
		errno = EINVAL;
		ret = -1;
	}
	ret = pthread_mutex_unlock(&__urcu_compat_futex_lock);
	if (ret) {
		errno = ret;
		ret = -1;
	}
end:
	return ret;
}

/*
 * _ASYNC SIGNAL-SAFE_.
 * For now, timeout, uaddr2 and val3 are unused.
 * Waiter will busy-loop trying to read the condition.
 */

int compat_futex_async(int32_t *uaddr, int op, int32_t val,
	const struct timespec *timeout, int32_t *uaddr2, int32_t val3)
{
	int ret = 0;

	/*
	 * Check if NULL. Don't let users expect that they are taken into
	 * account. 
	 */
	assert(!timeout);
	assert(!uaddr2);
	assert(!val3);

	/*
	 * Ensure previous memory operations on uaddr have completed.
	 */
	cmm_smp_mb();

	switch (op) {
	case FUTEX_WAIT:
		while (CMM_LOAD_SHARED(*uaddr) == val) {
			if (poll(NULL, 0, 10) < 0) {
				ret = -1;
				/* Keep poll errno. Caller handles EINTR. */
				goto end;
			}
		}
		break;
	case FUTEX_WAKE:
		break;
	default:
		errno = EINVAL;
		ret = -1;
	}
end:
	return ret;
}
Commit	Line	Data
	1	/*
	2	* compat_futex.c
	3	*
	4	* Userspace RCU library - sys_futex compatibility code
	5	*
	6	* Copyright (c) 2009 Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
	7	*
	8	* This library is free software; you can redistribute it and/or
	9	* modify it under the terms of the GNU Lesser General Public
	10	* License as published by the Free Software Foundation; either
	11	* version 2.1 of the License, or (at your option) any later version.
	12	*
	13	* This library is distributed in the hope that it will be useful,
	14	* but WITHOUT ANY WARRANTY; without even the implied warranty of
	15	* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
	16	* Lesser General Public License for more details.
	17	*
	18	* You should have received a copy of the GNU Lesser General Public
	19	* License along with this library; if not, write to the Free Software
	20	* Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
	21	*/
	22
	23	#include <stdio.h>
	24	#include <pthread.h>
	25	#include <signal.h>
	26	#include <assert.h>
	27	#include <errno.h>
	28	#include <poll.h>
	29	#include <stdint.h>
	30
	31	#include <urcu/arch.h>
	32	#include <urcu/futex.h>
	33	#include <urcu/system.h>
	34
	35	/*
	36	* Using attribute "weak" for __urcu_compat_futex_lock and
	37	* __urcu_compat_futex_cond. Those are globally visible by the entire
	38	* program, even though many shared objects may have their own version.
	39	* The first version that gets loaded will be used by the entire program
	40	* (executable and all shared objects).
	41	*/
	42
	43	__attribute__((weak))
	44	pthread_mutex_t __urcu_compat_futex_lock = PTHREAD_MUTEX_INITIALIZER;
	45	__attribute__((weak))
	46	pthread_cond_t __urcu_compat_futex_cond = PTHREAD_COND_INITIALIZER;
	47
	48	/*
	49	* _NOT SIGNAL-SAFE_. pthread_cond is not signal-safe anyway. Though.
	50	* For now, timeout, uaddr2 and val3 are unused.
	51	* Waiter will relinquish the CPU until woken up.
	52	*/
	53
	54	int compat_futex_noasync(int32_t *uaddr, int op, int32_t val,
	55	const struct timespec timeout, int32_t uaddr2, int32_t val3)
	56	{
	57	int ret;
	58
	59	/*
	60	* Check if NULL. Don't let users expect that they are taken into
	61	* account.
	62	*/
	63	assert(!timeout);
	64	assert(!uaddr2);
	65	assert(!val3);
	66
	67	/*
	68	* memory barriers to serialize with the previous uaddr modification.
	69	*/
	70	cmm_smp_mb();
	71
	72	ret = pthread_mutex_lock(&__urcu_compat_futex_lock);
	73	if (ret) {
	74	errno = ret;
	75	ret = -1;
	76	goto end;
	77	}
	78	switch (op) {
	79	case FUTEX_WAIT:
	80	/*
	81	* Wait until *uaddr is changed to something else than "val".
	82	* Comparing *uaddr content against val figures out which
	83	* thread has been awakened.
	84	*/
	85	while (CMM_LOAD_SHARED(*uaddr) == val)
	86	pthread_cond_wait(&__urcu_compat_futex_cond,
	87	&__urcu_compat_futex_lock);
	88	break;
	89	case FUTEX_WAKE:
	90	/*
	91	* Each wake is sending a broadcast, thus attempting wakeup of
	92	* all awaiting threads, independently of their respective
	93	* uaddr.
	94	*/
	95	pthread_cond_broadcast(&__urcu_compat_futex_cond);
	96	break;
	97	default:
	98	errno = EINVAL;
	99	ret = -1;
	100	}
	101	ret = pthread_mutex_unlock(&__urcu_compat_futex_lock);
	102	if (ret) {
	103	errno = ret;
	104	ret = -1;
	105	}
	106	end:
	107	return ret;
	108	}
	109
	110	/*
	111	* _ASYNC SIGNAL-SAFE_.
	112	* For now, timeout, uaddr2 and val3 are unused.
	113	* Waiter will busy-loop trying to read the condition.
	114	*/
	115
	116	int compat_futex_async(int32_t *uaddr, int op, int32_t val,
	117	const struct timespec timeout, int32_t uaddr2, int32_t val3)
	118	{
	119	int ret = 0;
	120
	121	/*
	122	* Check if NULL. Don't let users expect that they are taken into
	123	* account.
	124	*/
	125	assert(!timeout);
	126	assert(!uaddr2);
	127	assert(!val3);
	128
	129	/*
	130	* Ensure previous memory operations on uaddr have completed.
	131	*/
	132	cmm_smp_mb();
	133
	134	switch (op) {
	135	case FUTEX_WAIT:
	136	while (CMM_LOAD_SHARED(*uaddr) == val) {
	137	if (poll(NULL, 0, 10) < 0) {
	138	ret = -1;
	139	/* Keep poll errno. Caller handles EINTR. */
	140	goto end;
	141	}
	142	}
	143	break;
	144	case FUTEX_WAKE:
	145	break;
	146	default:
	147	errno = EINVAL;
	148	ret = -1;
	149	}
	150	end:
	151	return ret;
	152	}