/*-
 * 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.
 *
 * $FreeBSD: src/lib/libpthread/thread/thr_rwlock.c,v 1.14 2004/01/08 15:37:09 deischen Exp $
 */

#include "namespace.h"
#include <machine/tls.h>
#include <errno.h>
#include <limits.h>
#include <stdlib.h>
#include <pthread.h>
#include "un-namespace.h"
#include "thr_private.h"

#ifdef _PTHREADS_DEBUGGING

#include <stdio.h>
#include <stdarg.h>
#include <string.h>
#include <sys/file.h>

#endif

/* maximum number of times a read lock may be obtained */
#define MAX_READ_LOCKS          (INT_MAX - 1)

umtx_t  _rwlock_static_lock;

#ifdef _PTHREADS_DEBUGGING

static
void
rwlock_log(const char *ctl, ...)
{
        char buf[256];
        va_list va;
        size_t len;

        va_start(va, ctl);
        len = vsnprintf(buf, sizeof(buf), ctl, va);
        va_end(va);
        _thr_log(buf, len);
}

#else

static __inline
void
rwlock_log(const char *ctl __unused, ...)
{
}

#endif

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

        /* allocate rwlock object */
        prwlock = __malloc(sizeof(struct __pthread_rwlock_s));
        if (prwlock == NULL)
                return (ENOMEM);

        /* initialize the lock */
        if ((ret = _pthread_mutex_init(&prwlock->lock, NULL)) != 0) {
                __free(prwlock);
        } else {
                /* initialize the read condition signal */
                ret = _pthread_cond_init(&prwlock->read_signal, NULL);

                if (ret != 0) {
                        _pthread_mutex_destroy(&prwlock->lock);
                        __free(prwlock);
                } else {
                        /* initialize the write condition signal */
                        ret = _pthread_cond_init(&prwlock->write_signal, NULL);

                        if (ret != 0) {
                                _pthread_cond_destroy(&prwlock->read_signal);
                                _pthread_mutex_destroy(&prwlock->lock);
                                __free(prwlock);
                        } else {
                                /* success */
                                prwlock->state = 0;
                                prwlock->blocked_writers = 0;
                                *rwlock = prwlock;
                        }
                }
        }

        return (ret);
}

#if 0
void
_rwlock_reinit(pthread_rwlock_t prwlock)
{
        _mutex_reinit(&prwlock->lock);
        _cond_reinit(prwlock->read_signal);
        prwlock->state = 0;
        prwlock->blocked_writers = 0;
}
#endif

int
_pthread_rwlock_destroy (pthread_rwlock_t *rwlock)
{
        int ret;

        if (rwlock == NULL) {
                ret = EINVAL;
        } else if (*rwlock == NULL) {
                ret = 0;
        } else {
                pthread_rwlock_t prwlock;

                prwlock = *rwlock;
                rwlock_log("rwlock_destroy %p\n", prwlock);

                _pthread_mutex_destroy(&prwlock->lock);
                _pthread_cond_destroy(&prwlock->read_signal);
                _pthread_cond_destroy(&prwlock->write_signal);
                __free(prwlock);

                *rwlock = NULL;

                ret = 0;
        }
        return (ret);
}

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

        THR_LOCK_ACQUIRE(thread, &_rwlock_static_lock);

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

        THR_LOCK_RELEASE(thread, &_rwlock_static_lock);

        return (ret);
}

int
_pthread_rwlock_init(pthread_rwlock_t *rwlock, const pthread_rwlockattr_t *attr)
{
        *rwlock = NULL;
        return (rwlock_init(rwlock, attr));
}

static int
rwlock_rdlock_common(pthread_rwlock_t *rwlock, const struct timespec *abstime)
{
        pthread_t curthread = tls_get_curthread();
        pthread_rwlock_t prwlock;
        int ret;

        if (rwlock == NULL)
                return (EINVAL);

        prwlock = *rwlock;

        /* check for static initialization */
        if (prwlock == NULL) {
                if ((ret = init_static(curthread, rwlock)) != 0)
                        return (ret);

                prwlock = *rwlock;
        }
        rwlock_log("rwlock_rdlock_common %p\n", prwlock);

        /* grab the monitor lock */
        if ((ret = _pthread_mutex_lock(&prwlock->lock)) != 0) {
                rwlock_log("rwlock_rdlock_common %p (failedA)\n", prwlock);
                return (ret);
        }

        /* check lock count */
        if (prwlock->state == MAX_READ_LOCKS) {
                _pthread_mutex_unlock(&prwlock->lock);
                rwlock_log("rwlock_rdlock_common %p (failedB)\n", prwlock);
                return (EAGAIN);
        }

        curthread = tls_get_curthread();
        if ((curthread->rdlock_count > 0) && (prwlock->state > 0)) {
                /*
                 * 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 ;-)
                 */
                ;       /* nothing needed */
        } else {
                /*
                 * Give writers priority over readers
                 *
                 * WARNING: pthread_cond*() temporarily releases the
                 *          mutex.
                 */
                while (prwlock->blocked_writers || prwlock->state < 0) {
                        if (abstime) {
                                ret = _pthread_cond_timedwait(
                                            &prwlock->read_signal,
                                            &prwlock->lock, abstime);
                        } else {
                                ret = _pthread_cond_wait(
                                            &prwlock->read_signal,
                                            &prwlock->lock);
                        }
                        if (ret != 0) {
                                /* can't do a whole lot if this fails */
                                _pthread_mutex_unlock(&prwlock->lock);
                                rwlock_log("rwlock_rdlock_common %p "
                                           "(failedC)\n", prwlock);
                                return (ret);
                        }
                }
        }

        curthread->rdlock_count++;
        prwlock->state++; /* indicate we are locked for reading */

        /*
         * Something is really wrong if this call fails.  Returning
         * error won't do because we've already obtained the read
         * lock.  Decrementing 'state' is no good because we probably
         * don't have the monitor lock.
         */
        _pthread_mutex_unlock(&prwlock->lock);
        rwlock_log("rwlock_rdlock_common %p (return %d)\n", prwlock, ret);

        return (ret);
}

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

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

int
_pthread_rwlock_tryrdlock (pthread_rwlock_t *rwlock)
{
        pthread_t curthread = tls_get_curthread();
        pthread_rwlock_t prwlock;
        int ret;

        if (rwlock == NULL)
                return (EINVAL);

        prwlock = *rwlock;

        /* check for static initialization */
        if (prwlock == NULL) {
                if ((ret = init_static(curthread, rwlock)) != 0)
                        return (ret);

                prwlock = *rwlock;
        }

        /* grab the monitor lock */
        if ((ret = _pthread_mutex_lock(&prwlock->lock)) != 0)
                return (ret);

        curthread = tls_get_curthread();
        if (prwlock->state == MAX_READ_LOCKS)
                ret = EAGAIN;
        else if ((curthread->rdlock_count > 0) && (prwlock->state > 0)) {
                /* see comment for pthread_rwlock_rdlock() */
                curthread->rdlock_count++;
                prwlock->state++;
        }
        /* give writers priority over readers */
        else if (prwlock->blocked_writers || prwlock->state < 0)
                ret = EBUSY;
        else {
                curthread->rdlock_count++;
                prwlock->state++; /* indicate we are locked for reading */
        }

        /* see the comment on this in pthread_rwlock_rdlock */
        _pthread_mutex_unlock(&prwlock->lock);

        return (ret);
}

int
_pthread_rwlock_trywrlock (pthread_rwlock_t *rwlock)
{
        pthread_t curthread = tls_get_curthread();
        pthread_rwlock_t prwlock;
        int ret;

        if (rwlock == NULL)
                return (EINVAL);

        prwlock = *rwlock;

        /* check for static initialization */
        if (prwlock == NULL) {
                if ((ret = init_static(curthread, rwlock)) != 0)
                        return (ret);

                prwlock = *rwlock;
        }

        /* grab the monitor lock */
        if ((ret = _pthread_mutex_lock(&prwlock->lock)) != 0)
                return (ret);

        if (prwlock->state != 0)
                ret = EBUSY;
        else
                /* indicate we are locked for writing */
                prwlock->state = -1;

        /* see the comment on this in pthread_rwlock_rdlock */
        _pthread_mutex_unlock(&prwlock->lock);

        return (ret);
}

int
_pthread_rwlock_unlock (pthread_rwlock_t *rwlock)
{
        pthread_t curthread;
        pthread_rwlock_t prwlock;
        int ret;

        if (rwlock == NULL)
                return (EINVAL);

        prwlock = *rwlock;

        if (prwlock == NULL)
                return (EINVAL);

        rwlock_log("rwlock_unlock %p\n", prwlock);

        /* grab the monitor lock */
        if ((ret = _pthread_mutex_lock(&prwlock->lock)) != 0)
                return (ret);

        curthread = tls_get_curthread();
        if (prwlock->state > 0) {
                /*
                 * Unlock reader
                 */
                curthread->rdlock_count--;
                prwlock->state--;
                if (prwlock->state == 0 && prwlock->blocked_writers)
                        ret = _pthread_cond_signal(&prwlock->write_signal);
        } else if (prwlock->state < 0) {
                /*
                 * unlock writer
                 */
                prwlock->state = 0;

                if (prwlock->blocked_writers)
                        ret = _pthread_cond_signal(&prwlock->write_signal);
                else
                        ret = _pthread_cond_broadcast(&prwlock->read_signal);
        } else {
                ret = EINVAL;
        }

        /* see the comment on this in pthread_rwlock_rdlock */
        _pthread_mutex_unlock(&prwlock->lock);
        rwlock_log("rwlock_unlock %p (return %d)\n", prwlock, ret);

        return (ret);
}

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

        if (rwlock == NULL)
                return (EINVAL);

        prwlock = *rwlock;

        /* check for static initialization */
        if (prwlock == NULL) {
                if ((ret = init_static(curthread, rwlock)) != 0)
                        return (ret);

                prwlock = *rwlock;
        }
        rwlock_log("rwlock_wrlock_common %p\n", prwlock);

        /* grab the monitor lock */
        if ((ret = _pthread_mutex_lock(&prwlock->lock)) != 0) {
                rwlock_log("rwlock_wrlock_common %p (failedA)\n", prwlock);
                return (ret);
        }

        while (prwlock->state != 0) {
                prwlock->blocked_writers++;

                /*
                 * WARNING: pthread_cond*() temporarily releases the
                 *          mutex.
                 */
                if (abstime != NULL) {
                        ret = _pthread_cond_timedwait(&prwlock->write_signal,
                                                      &prwlock->lock,
                                                      abstime);
                } else {
                        ret = _pthread_cond_wait(&prwlock->write_signal,
                                                 &prwlock->lock);
                }

                /*
                 * Undo on failure.  When the blocked_writers count drops
                 * to 0 we may have to wakeup blocked readers.
                 */
                if (ret != 0) {
                        prwlock->blocked_writers--;
                        if (prwlock->blocked_writers == 0 &&
                            prwlock->state >= 0) {
                                _pthread_cond_broadcast(&prwlock->read_signal);
                        }
                        _pthread_mutex_unlock(&prwlock->lock);
                        rwlock_log("rwlock_wrlock_common %p (failedB %d)\n",
                                   prwlock, ret);
                        return (ret);
                }

                prwlock->blocked_writers--;
        }

        /* indicate we are locked for writing */
        prwlock->state = -1;

        /* see the comment on this in pthread_rwlock_rdlock */
        _pthread_mutex_unlock(&prwlock->lock);
        rwlock_log("rwlock_wrlock_common %p (returns %d)\n", prwlock, ret);

        return (ret);
}

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

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

__strong_reference(_pthread_rwlock_destroy, pthread_rwlock_destroy);
__strong_reference(_pthread_rwlock_init, pthread_rwlock_init);
__strong_reference(_pthread_rwlock_rdlock, pthread_rwlock_rdlock);
__strong_reference(_pthread_rwlock_timedrdlock, pthread_rwlock_timedrdlock);
__strong_reference(_pthread_rwlock_tryrdlock, pthread_rwlock_tryrdlock);
__strong_reference(_pthread_rwlock_trywrlock, pthread_rwlock_trywrlock);
__strong_reference(_pthread_rwlock_unlock, pthread_rwlock_unlock);
__strong_reference(_pthread_rwlock_wrlock, pthread_rwlock_wrlock);
__strong_reference(_pthread_rwlock_timedwrlock, pthread_rwlock_timedwrlock);