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/*-
* Copyright (c) 2001, 2003 Daniel Eischen <deischen@freebsd.org>.
* All rights reserved.
*
* Redistribution and use in source and binary forms, with or without
* modification, are permitted provided that the following conditions
* are met:
* 1. Redistributions of source code must retain the above copyright
* notice, this list of conditions and the following disclaimer.
* 2. Redistributions in binary form must reproduce the above copyright
* notice, this list of conditions and the following disclaimer in the
* documentation and/or other materials provided with the distribution.
*
* THIS SOFTWARE IS PROVIDED BY THE AUTHORS AND CONTRIBUTORS ``AS IS'' AND
* ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
* IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
* ARE DISCLAIMED. IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE
* FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
* DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
* OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
* HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
* LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
* OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
* SUCH DAMAGE.
*
* $FreeBSD$
*/
#include <sys/types.h>
#include <machine/atomic.h>
#include <assert.h>
#include <stdlib.h>
#include "atomic_ops.h"
#include "lock.h"
#ifdef _LOCK_DEBUG
#define LCK_ASSERT(e) assert(e)
#else
#define LCK_ASSERT(e)
#endif
#define MAX_SPINS 500
void
_lock_destroy(struct lock *lck)
{
if ((lck != NULL) && (lck->l_head != NULL)) {
free(lck->l_head);
lck->l_head = NULL;
lck->l_tail = NULL;
}
}
int
_lock_init(struct lock *lck, enum lock_type ltype,
lock_handler_t *waitfunc, lock_handler_t *wakeupfunc)
{
if (lck == NULL)
return (-1);
else if ((lck->l_head = malloc(sizeof(struct lockreq))) == NULL)
return (-1);
else {
lck->l_type = ltype;
lck->l_wait = waitfunc;
lck->l_wakeup = wakeupfunc;
lck->l_head->lr_locked = 0;
lck->l_head->lr_watcher = NULL;
lck->l_head->lr_owner = NULL;
lck->l_head->lr_active = 1;
lck->l_tail = lck->l_head;
}
return (0);
}
int
_lockuser_init(struct lockuser *lu, void *priv)
{
if (lu == NULL)
return (-1);
else if ((lu->lu_myreq == NULL) &&
((lu->lu_myreq = malloc(sizeof(struct lockreq))) == NULL))
return (-1);
else {
lu->lu_myreq->lr_locked = 1;
lu->lu_myreq->lr_watcher = NULL;
lu->lu_myreq->lr_owner = lu;
lu->lu_myreq->lr_active = 0;
lu->lu_watchreq = NULL;
lu->lu_priority = 0;
lu->lu_private = priv;
lu->lu_private2 = NULL;
}
return (0);
}
void
_lockuser_destroy(struct lockuser *lu)
{
if ((lu != NULL) && (lu->lu_myreq != NULL))
free(lu->lu_myreq);
}
/*
* Acquire a lock waiting (spin or sleep) for it to become available.
*/
void
_lock_acquire(struct lock *lck, struct lockuser *lu, int prio)
{
int i;
int lval;
/**
* XXX - We probably want to remove these checks to optimize
* performance. It is also a bug if any one of the
* checks fail, so it's probably better to just let it
* SEGV and fix it.
*/
#if 0
if (lck == NULL || lu == NULL || lck->l_head == NULL)
return;
#endif
if ((lck->l_type & LCK_PRIORITY) == 0)
atomic_swap_ptr(&lck->l_head, lu->lu_myreq, &lu->lu_watchreq);
else {
LCK_ASSERT(lu->lu_myreq->lr_locked == 1);
LCK_ASSERT(lu->lu_myreq->lr_watcher == NULL);
LCK_ASSERT(lu->lu_myreq->lr_owner == lu);
LCK_ASSERT(lu->lu_watchreq == NULL);
lu->lu_priority = prio;
/*
* Atomically swap the head of the lock request with
* this request.
*/
atomic_swap_ptr(&lck->l_head, lu->lu_myreq, &lu->lu_watchreq);
}
if (lu->lu_watchreq->lr_locked != 0) {
atomic_store_rel_ptr(&lu->lu_watchreq->lr_watcher, lu);
if ((lck->l_wait == NULL) ||
((lck->l_type & LCK_ADAPTIVE) == 0)) {
while (lu->lu_watchreq->lr_locked == 0)
; /* spin, then yield? */
} else {
/*
* Spin for a bit before invoking the wait function.
*
* We should be a little smarter here. If we're
* running on a single processor, then the lock
* owner got preempted and spinning will accomplish
* nothing but waste time. If we're running on
* multiple processors, the owner could be running
* on another CPU and we might acquire the lock if
* we spin for a bit.
*
* The other thing to keep in mind is that threads
* acquiring these locks are considered to be in
* critical regions; they will not be preempted by
* the _UTS_ until they release the lock. It is
* therefore safe to assume that if a lock can't
* be acquired, it is currently held by a thread
* running in another KSE.
*/
for (i = 0; i < MAX_SPINS; i++) {
if (lu->lu_watchreq->lr_locked == 0)
return;
if (lu->lu_watchreq->lr_active == 0)
break;
}
atomic_swap_int((int *)&lu->lu_watchreq->lr_locked,
2, &lval);
if (lval == 0)
lu->lu_watchreq->lr_locked = 0;
else
lck->l_wait(lck, lu);
}
}
lu->lu_myreq->lr_active = 1;
}
/*
* Release a lock.
*/
void
_lock_release(struct lock *lck, struct lockuser *lu)
{
struct lockuser *lu_tmp, *lu_h;
struct lockreq *myreq;
int prio_h;
int lval;
/**
* XXX - We probably want to remove these checks to optimize
* performance. It is also a bug if any one of the
* checks fail, so it's probably better to just let it
* SEGV and fix it.
*/
#if 0
if ((lck == NULL) || (lu == NULL))
return;
#endif
if ((lck->l_type & LCK_PRIORITY) != 0) {
prio_h = 0;
lu_h = NULL;
/* Update tail if our request is last. */
if (lu->lu_watchreq->lr_owner == NULL) {
atomic_store_rel_ptr(&lck->l_tail, lu->lu_myreq);
atomic_store_rel_ptr(&lu->lu_myreq->lr_owner, NULL);
} else {
/* Remove ourselves from the list. */
atomic_store_rel_ptr(&lu->lu_myreq->lr_owner,
lu->lu_watchreq->lr_owner);
atomic_store_rel_ptr(
&lu->lu_watchreq->lr_owner->lu_myreq, lu->lu_myreq);
}
/*
* The watch request now becomes our own because we've
* traded away our previous request. Save our previous
* request so that we can grant the lock.
*/
myreq = lu->lu_myreq;
lu->lu_myreq = lu->lu_watchreq;
lu->lu_watchreq = NULL;
lu->lu_myreq->lr_locked = 1;
lu->lu_myreq->lr_owner = lu;
lu->lu_myreq->lr_watcher = NULL;
/*
* Traverse the list of lock requests in reverse order
* looking for the user with the highest priority.
*/
for (lu_tmp = lck->l_tail->lr_watcher; lu_tmp != NULL;
lu_tmp = lu_tmp->lu_myreq->lr_watcher) {
if (lu_tmp->lu_priority > prio_h) {
lu_h = lu_tmp;
prio_h = lu_tmp->lu_priority;
}
}
if (lu_h != NULL) {
/* Give the lock to the highest priority user. */
if (lck->l_wakeup != NULL) {
atomic_swap_int(
(int *)&lu_h->lu_watchreq->lr_locked,
0, &lval);
if (lval == 2)
/* Notify the sleeper */
lck->l_wakeup(lck,
lu_h->lu_myreq->lr_watcher);
}
else
atomic_store_rel_int(
&lu_h->lu_watchreq->lr_locked, 0);
} else {
if (lck->l_wakeup != NULL) {
atomic_swap_int((int *)&myreq->lr_locked,
0, &lval);
if (lval == 2)
/* Notify the sleeper */
lck->l_wakeup(lck, myreq->lr_watcher);
}
else
/* Give the lock to the previous request. */
atomic_store_rel_int(&myreq->lr_locked, 0);
}
} else {
/*
* The watch request now becomes our own because we've
* traded away our previous request. Save our previous
* request so that we can grant the lock.
*/
myreq = lu->lu_myreq;
lu->lu_myreq = lu->lu_watchreq;
lu->lu_watchreq = NULL;
lu->lu_myreq->lr_locked = 1;
if (lck->l_wakeup) {
atomic_swap_int((int *)&myreq->lr_locked, 0, &lval);
if (lval == 2)
/* Notify the sleeper */
lck->l_wakeup(lck, myreq->lr_watcher);
}
else
/* Give the lock to the previous request. */
atomic_store_rel_int(&myreq->lr_locked, 0);
}
lu->lu_myreq->lr_active = 0;
}
void
_lock_grant(struct lock *lck /* unused */, struct lockuser *lu)
{
atomic_store_rel_int(&lu->lu_watchreq->lr_locked, 3);
}
void
_lockuser_setactive(struct lockuser *lu, int active)
{
lu->lu_myreq->lr_active = active;
}
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