/*-
 * SPDX-License-Identifier: BSD-2-Clause
 *
 * Copyright (c) 1998 Alex Nash
 * 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 AUTHOR 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.
 */

#include <errno.h>
#include <limits.h>
#include <stdlib.h>
#include <string.h>

#include "namespace.h"
#include <pthread.h>
#include "un-namespace.h"
#include "thr_private.h"

_Static_assert(sizeof(struct pthread_rwlock) <= THR_PAGE_SIZE_MIN,
    "pthread_rwlock is too large for off-page");

__weak_reference(_thr_rwlock_destroy, pthread_rwlock_destroy);
__weak_reference(_thr_rwlock_destroy, _pthread_rwlock_destroy);
__weak_reference(_thr_rwlock_init, pthread_rwlock_init);
__weak_reference(_thr_rwlock_init, _pthread_rwlock_init);
__weak_reference(_Tthr_rwlock_rdlock, pthread_rwlock_rdlock);
__weak_reference(_Tthr_rwlock_rdlock, _pthread_rwlock_rdlock);
__weak_reference(_pthread_rwlock_timedrdlock, pthread_rwlock_timedrdlock);
__weak_reference(_Tthr_rwlock_tryrdlock, pthread_rwlock_tryrdlock);
__weak_reference(_Tthr_rwlock_tryrdlock, _pthread_rwlock_tryrdlock);
__weak_reference(_Tthr_rwlock_trywrlock, pthread_rwlock_trywrlock);
__weak_reference(_Tthr_rwlock_trywrlock, _pthread_rwlock_trywrlock);
__weak_reference(_Tthr_rwlock_unlock, pthread_rwlock_unlock);
__weak_reference(_Tthr_rwlock_unlock, _pthread_rwlock_unlock);
__weak_reference(_Tthr_rwlock_wrlock, pthread_rwlock_wrlock);
__weak_reference(_Tthr_rwlock_wrlock, _pthread_rwlock_wrlock);
__weak_reference(_pthread_rwlock_timedwrlock, pthread_rwlock_timedwrlock);

static int init_static(struct pthread *thread, pthread_rwlock_t *rwlock);
static int init_rwlock(pthread_rwlock_t *rwlock, pthread_rwlock_t *rwlock_out);

static __always_inline int
check_and_init_rwlock(pthread_rwlock_t *rwlock, pthread_rwlock_t *rwlock_out)
{
        if (__predict_false(*rwlock == THR_PSHARED_PTR ||
            *rwlock <= THR_RWLOCK_DESTROYED))
                return (init_rwlock(rwlock, rwlock_out));
        *rwlock_out = *rwlock;
        return (0);
}

static int __noinline
init_rwlock(pthread_rwlock_t *rwlock, pthread_rwlock_t *rwlock_out)
{
        pthread_rwlock_t prwlock;
        int ret;

        if (*rwlock == THR_PSHARED_PTR) {
                prwlock = __thr_pshared_offpage(rwlock, 0);
                if (prwlock == NULL)
                        return (EINVAL);
        } else if ((prwlock = *rwlock) <= THR_RWLOCK_DESTROYED) {
                if (prwlock == THR_RWLOCK_INITIALIZER) {
                        ret = init_static(_get_curthread(), rwlock);
                        if (ret != 0)
                                return (ret);
                } else if (prwlock == THR_RWLOCK_DESTROYED) {
                        return (EINVAL);
                }
                prwlock = *rwlock;
        }
        *rwlock_out = prwlock;
        return (0);
}

static int
rwlock_init(pthread_rwlock_t *rwlock, const pthread_rwlockattr_t *attr)
{
        pthread_rwlock_t prwlock;

        if (attr == NULL || *attr == NULL ||
            (*attr)->pshared == PTHREAD_PROCESS_PRIVATE) {
                prwlock = aligned_alloc(CACHE_LINE_SIZE,
                    roundup(sizeof(struct pthread_rwlock), CACHE_LINE_SIZE));
                if (prwlock == NULL)
                        return (ENOMEM);
                memset(prwlock, 0, sizeof(struct pthread_rwlock));
                *rwlock = prwlock;
        } else {
                prwlock = __thr_pshared_offpage(rwlock, 1);
                if (prwlock == NULL)
                        return (EFAULT);
                prwlock->lock.rw_flags |= USYNC_PROCESS_SHARED;
                *rwlock = THR_PSHARED_PTR;
        }
        return (0);
}

int
_thr_rwlock_destroy(pthread_rwlock_t *rwlock)
{
        pthread_rwlock_t prwlock;
        int ret;

        prwlock = *rwlock;
        if (prwlock == THR_RWLOCK_INITIALIZER)
                ret = 0;
        else if (prwlock == THR_RWLOCK_DESTROYED)
                ret = EINVAL;
        else if (prwlock == THR_PSHARED_PTR) {
                *rwlock = THR_RWLOCK_DESTROYED;
                __thr_pshared_destroy(rwlock);
                ret = 0;
        } else {
                *rwlock = THR_RWLOCK_DESTROYED;
                free(prwlock);
                ret = 0;
        }
        return (ret);
}

static int
init_static(struct pthread *thread, pthread_rwlock_t *rwlock)
{
        int ret;

        THR_LOCK_ACQUIRE(thread, &_rwlock_static_lock);

        if (*rwlock == THR_RWLOCK_INITIALIZER)
                ret = rwlock_init(rwlock, NULL);
        else
                ret = 0;

        THR_LOCK_RELEASE(thread, &_rwlock_static_lock);

        return (ret);
}

int
_thr_rwlock_init(pthread_rwlock_t *rwlock, const pthread_rwlockattr_t *attr)
{

        _thr_check_init();
        *rwlock = NULL;
        return (rwlock_init(rwlock, attr));
}

static int
rwlock_rdlock_common(pthread_rwlock_t *rwlock, const struct timespec *abstime)
{
        struct pthread *curthread = _get_curthread();
        pthread_rwlock_t prwlock;
        int flags;
        int ret;

        ret = check_and_init_rwlock(rwlock, &prwlock);
        if (ret != 0)
                return (ret);

        if (curthread->rdlock_count) {
                /*
                 * To avoid having to track all the rdlocks held by
                 * a thread or all of the threads that hold a rdlock,
                 * we keep a simple count of all the rdlocks held by
                 * a thread.  If a thread holds any rdlocks it is
                 * possible that it is attempting to take a recursive
                 * rdlock.  If there are blocked writers and precedence
                 * is given to them, then that would result in the thread
                 * deadlocking.  So allowing a thread to take the rdlock
                 * when it already has one or more rdlocks avoids the
                 * deadlock.  I hope the reader can follow that logic ;-)
                 */
                flags = URWLOCK_PREFER_READER;
        } else {
                flags = 0;
        }

        /*
         * POSIX said the validity of the abstimeout parameter need
         * not be checked if the lock can be immediately acquired.
         */
        ret = _thr_rwlock_tryrdlock(&prwlock->lock, flags);
        if (ret == 0) {
                curthread->rdlock_count++;
                return (ret);
        }

        if (__predict_false(abstime && 
                (abstime->tv_nsec >= 1000000000 || abstime->tv_nsec < 0)))
                return (EINVAL);

        for (;;) {
                /* goto kernel and lock it */
                ret = __thr_rwlock_rdlock(&prwlock->lock, flags, abstime);
                if (ret != EINTR)
                        break;

                /* if interrupted, try to lock it in userland again. */
                if (_thr_rwlock_tryrdlock(&prwlock->lock, flags) == 0) {
                        ret = 0;
                        break;
                }
        }
        if (ret == 0)
                curthread->rdlock_count++;
        return (ret);
}

int
_Tthr_rwlock_rdlock(pthread_rwlock_t *rwlock)
{
        _thr_check_init();
        return (rwlock_rdlock_common(rwlock, NULL));
}

int
_pthread_rwlock_timedrdlock(pthread_rwlock_t * __restrict rwlock,
    const struct timespec * __restrict abstime)
{
        _thr_check_init();
        return (rwlock_rdlock_common(rwlock, abstime));
}

int
_Tthr_rwlock_tryrdlock(pthread_rwlock_t *rwlock)
{
        struct pthread *curthread;
        pthread_rwlock_t prwlock;
        int flags;
        int ret;

        _thr_check_init();
        ret = check_and_init_rwlock(rwlock, &prwlock);
        if (ret != 0)
                return (ret);

        curthread = _get_curthread();
        if (curthread->rdlock_count) {
                /*
                 * To avoid having to track all the rdlocks held by
                 * a thread or all of the threads that hold a rdlock,
                 * we keep a simple count of all the rdlocks held by
                 * a thread.  If a thread holds any rdlocks it is
                 * possible that it is attempting to take a recursive
                 * rdlock.  If there are blocked writers and precedence
                 * is given to them, then that would result in the thread
                 * deadlocking.  So allowing a thread to take the rdlock
                 * when it already has one or more rdlocks avoids the
                 * deadlock.  I hope the reader can follow that logic ;-)
                 */
                flags = URWLOCK_PREFER_READER;
        } else {
                flags = 0;
        }

        ret = _thr_rwlock_tryrdlock(&prwlock->lock, flags);
        if (ret == 0)
                curthread->rdlock_count++;
        return (ret);
}

int
_Tthr_rwlock_trywrlock(pthread_rwlock_t *rwlock)
{
        struct pthread *curthread;
        pthread_rwlock_t prwlock;
        int ret;

        _thr_check_init();
        ret = check_and_init_rwlock(rwlock, &prwlock);
        if (ret != 0)
                return (ret);

        curthread = _get_curthread();
        ret = _thr_rwlock_trywrlock(&prwlock->lock);
        if (ret == 0)
                prwlock->owner = TID(curthread);
        return (ret);
}

static int
rwlock_wrlock_common(pthread_rwlock_t *rwlock, const struct timespec *abstime)
{
        struct pthread *curthread = _get_curthread();
        pthread_rwlock_t prwlock;
        int ret;

        ret = check_and_init_rwlock(rwlock, &prwlock);
        if (ret != 0)
                return (ret);

        /*
         * POSIX said the validity of the abstimeout parameter need
         * not be checked if the lock can be immediately acquired.
         */
        ret = _thr_rwlock_trywrlock(&prwlock->lock);
        if (ret == 0) {
                prwlock->owner = TID(curthread);
                return (ret);
        }

        if (__predict_false(abstime && 
            (abstime->tv_nsec >= 1000000000 || abstime->tv_nsec < 0)))
                return (EINVAL);

        for (;;) {
                /* goto kernel and lock it */
                ret = __thr_rwlock_wrlock(&prwlock->lock, abstime);
                if (ret == 0) {
                        prwlock->owner = TID(curthread);
                        break;
                }

                if (ret != EINTR)
                        break;

                /* if interrupted, try to lock it in userland again. */
                if (_thr_rwlock_trywrlock(&prwlock->lock) == 0) {
                        ret = 0;
                        prwlock->owner = TID(curthread);
                        break;
                }
        }
        return (ret);
}

int
_Tthr_rwlock_wrlock(pthread_rwlock_t *rwlock)
{
        _thr_check_init();
        return (rwlock_wrlock_common(rwlock, NULL));
}

int
_pthread_rwlock_timedwrlock(pthread_rwlock_t * __restrict rwlock,
    const struct timespec * __restrict abstime)
{
        _thr_check_init();
        return (rwlock_wrlock_common(rwlock, abstime));
}

int
_Tthr_rwlock_unlock(pthread_rwlock_t *rwlock)
{
        struct pthread *curthread = _get_curthread();
        pthread_rwlock_t prwlock;
        int ret;
        int32_t state;

        if (*rwlock == THR_PSHARED_PTR) {
                prwlock = __thr_pshared_offpage(rwlock, 0);
                if (prwlock == NULL)
                        return (EINVAL);
        } else {
                prwlock = *rwlock;
        }

        if (__predict_false(prwlock <= THR_RWLOCK_DESTROYED))
                return (EINVAL);

        state = prwlock->lock.rw_state;
        if (state & URWLOCK_WRITE_OWNER) {
                if (__predict_false(prwlock->owner != TID(curthread)))
                        return (EPERM);
                prwlock->owner = 0;
        }

        ret = _thr_rwlock_unlock(&prwlock->lock);
        if (ret == 0 && (state & URWLOCK_WRITE_OWNER) == 0)
                curthread->rdlock_count--;

        return (ret);
}