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/*
* "Sequence" lock primitive
*
* Copyright (C) 2015 David Lamparter <equinox@diac24.net>
*
* 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
*/
#define _GNU_SOURCE
#ifdef HAVE_CONFIG_H
#include "config.h"
#endif
#include <unistd.h>
#include <limits.h>
#include <errno.h>
#include <sys/types.h>
#include <sys/time.h>
#include <pthread.h>
#include <assert.h>
#include "seqlock.h"
#ifdef HAVE_SYNC_LINUX_FUTEX
/* Linux-specific - sys_futex() */
#include <sys/syscall.h>
#include <linux/futex.h>
static long sys_futex(void *addr1, int op, int val1, struct timespec *timeout,
void *addr2, int val3)
{
return syscall(SYS_futex, addr1, op, val1, timeout, addr2, val3);
}
#define wait_once(sqlo, val) \
sys_futex((int *)&sqlo->pos, FUTEX_WAIT, (int)val, NULL, NULL, 0)
#define wait_poke(sqlo) \
sys_futex((int *)&sqlo->pos, FUTEX_WAKE, INT_MAX, NULL, NULL, 0)
#elif defined(HAVE_SYNC_OPENBSD_FUTEX)
/* OpenBSD variant of the above. untested, not upstream in OpenBSD. */
#include <sys/syscall.h>
#include <sys/futex.h>
#define wait_once(sqlo, val) \
futex((int *)&sqlo->pos, FUTEX_WAIT, (int)val, NULL, NULL, 0)
#define wait_poke(sqlo) \
futex((int *)&sqlo->pos, FUTEX_WAKE, INT_MAX, NULL, NULL, 0)
#elif defined(HAVE_SYNC_UMTX_OP)
/* FreeBSD-specific: umtx_op() */
#include <sys/umtx.h>
#define wait_once(sqlo, val) \
_umtx_op((void *)&sqlo->pos, UMTX_OP_WAIT_UINT, val, NULL, NULL)
#define wait_poke(sqlo) \
_umtx_op((void *)&sqlo->pos, UMTX_OP_WAKE, INT_MAX, NULL, NULL)
#else
/* generic version. used on *BSD, Solaris and OSX.
*/
#define wait_init(sqlo) do { \
pthread_mutex_init(&sqlo->lock, NULL); \
pthread_cond_init(&sqlo->wake, NULL); \
} while (0)
#define wait_prep(sqlo) pthread_mutex_lock(&sqlo->lock)
#define wait_once(sqlo, val) pthread_cond_wait(&sqlo->wake, &sqlo->lock)
#define wait_done(sqlo) pthread_mutex_unlock(&sqlo->lock)
#define wait_poke(sqlo) do { \
pthread_mutex_lock(&sqlo->lock); \
pthread_cond_broadcast(&sqlo->wake); \
pthread_mutex_unlock(&sqlo->lock); \
} while (0)
#endif
#ifndef wait_init
#define wait_init(sqlo) /**/
#define wait_prep(sqlo) /**/
#define wait_done(sqlo) /**/
#endif /* wait_init */
void seqlock_wait(struct seqlock *sqlo, seqlock_val_t val)
{
seqlock_val_t cur, cal;
seqlock_assert_valid(val);
wait_prep(sqlo);
while (1) {
cur = atomic_load_explicit(&sqlo->pos, memory_order_acquire);
if (!(cur & 1))
break;
cal = cur - val - 1;
assert(cal < 0x40000000 || cal > 0xc0000000);
if (cal < 0x80000000)
break;
wait_once(sqlo, cur);
}
wait_done(sqlo);
}
bool seqlock_check(struct seqlock *sqlo, seqlock_val_t val)
{
seqlock_val_t cur;
seqlock_assert_valid(val);
cur = atomic_load_explicit(&sqlo->pos, memory_order_acquire);
if (!(cur & 1))
return 1;
cur -= val;
assert(cur < 0x40000000 || cur > 0xc0000000);
return cur < 0x80000000;
}
void seqlock_acquire_val(struct seqlock *sqlo, seqlock_val_t val)
{
seqlock_assert_valid(val);
atomic_store_explicit(&sqlo->pos, val, memory_order_release);
wait_poke(sqlo);
}
void seqlock_release(struct seqlock *sqlo)
{
atomic_store_explicit(&sqlo->pos, 0, memory_order_release);
wait_poke(sqlo);
}
void seqlock_init(struct seqlock *sqlo)
{
sqlo->pos = 0;
wait_init(sqlo);
}
seqlock_val_t seqlock_cur(struct seqlock *sqlo)
{
return atomic_load_explicit(&sqlo->pos, memory_order_acquire);
}
seqlock_val_t seqlock_bump(struct seqlock *sqlo)
{
seqlock_val_t val;
val = atomic_fetch_add_explicit(&sqlo->pos, 2, memory_order_release);
wait_poke(sqlo);
return val;
}
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