/*
 * CDDL HEADER START
 *
 * The contents of this file are subject to the terms of the
 * Common Development and Distribution License (the "License").
 * You may not use this file except in compliance with the License.
 *
 * You can obtain a copy of the license at usr/src/OPENSOLARIS.LICENSE
 * or http://www.opensolaris.org/os/licensing.
 * See the License for the specific language governing permissions
 * and limitations under the License.
 *
 * When distributing Covered Code, include this CDDL HEADER in each
 * file and include the License file at usr/src/OPENSOLARIS.LICENSE.
 * If applicable, add the following below this CDDL HEADER, with the
 * fields enclosed by brackets "[]" replaced with your own identifying
 * information: Portions Copyright [yyyy] [name of copyright owner]
 *
 * CDDL HEADER END
 */

/*
 * Copyright 2009 Sun Microsystems, Inc.  All rights reserved.
 * Use is subject to license terms.
 */

#ifndef _SYS_CONDVAR_IMPL_H
#define _SYS_CONDVAR_IMPL_H

/*
 * Implementation-private definitions for condition variables
 */

#ifndef _ASM
#include <sys/types.h>
#include <sys/thread.h>
#endif  /* _ASM */

#ifdef  __cplusplus
extern "C" {
#endif

#ifndef _ASM

/*
 * Condtion variables.
 */

typedef struct _condvar_impl {
        ushort_t        cv_waiters;
} condvar_impl_t;

#define CV_HAS_WAITERS(cvp)     (((condvar_impl_t *)(cvp))->cv_waiters != 0)

#endif  /* _ASM */


/*
 * The cvwaitlock_t structure and associated macros provide an implementation
 * of a locking mechanism that allows recursion on the reader lock without
 * danger of a pending write lock elsewhere being able to cause a deadlock.
 * The provision for supporting recursion is necessary for use with the
 * netinfo (neti) kernel module when processing network data.
 *
 * Support for recursion (giving precedence to readers and allowing them
 * to enter even when a write is blocked) can result in write starvation.
 * There is no priority inheritence for this locking interface.
 */
typedef struct  cvwaitlock_s    {
        kmutex_t        cvw_lock;
        kcondvar_t      cvw_waiter;
        int             cvw_refcnt;
} cvwaitlock_t;


#define CVW_INIT(_c)            {                               \
        mutex_init(&(_c)->cvw_lock, NULL, MUTEX_DRIVER, NULL);  \
        cv_init(&(_c)->cvw_waiter, NULL, CV_DRIVER, NULL);      \
        (_c)->cvw_refcnt = 0;                                   \
}

#define CVW_ENTER_READ(_c)      {                               \
        mutex_enter(&(_c)->cvw_lock);                           \
        while ((_c)->cvw_refcnt < 0)                            \
                cv_wait(&((_c)->cvw_waiter), &(_c)->cvw_lock);  \
        (_c)->cvw_refcnt++;                                     \
        mutex_exit(&(_c)->cvw_lock);                            \
}

#define CVW_ENTER_WRITE(_c)     {                               \
        mutex_enter(&(_c)->cvw_lock);                           \
        while ((_c)->cvw_refcnt != 0)                           \
                cv_wait(&((_c)->cvw_waiter), &(_c)->cvw_lock);  \
        (_c)->cvw_refcnt = -1;                                  \
        mutex_exit(&(_c)->cvw_lock);                            \
}

#define CVW_EXIT_READ(_c)       {                       \
        mutex_enter(&(_c)->cvw_lock);                   \
        ASSERT((_c)->cvw_refcnt > 0);                   \
        if ((--((_c)->cvw_refcnt)) == 0)                \
                cv_broadcast(&(_c)->cvw_waiter);        \
        mutex_exit(&(_c)->cvw_lock);                    \
}

#define CVW_EXIT_WRITE(_c)      {                       \
        mutex_enter(&(_c)->cvw_lock);                   \
        ASSERT((_c)->cvw_refcnt == -1);                 \
        (_c)->cvw_refcnt = 0;                           \
        cv_broadcast(&(_c)->cvw_waiter);                \
        mutex_exit(&(_c)->cvw_lock);                    \
}

#define CVW_WRITE_TO_READ(_c)   {                       \
        mutex_enter(&(_c)->cvw_lock);                   \
        ASSERT((_c)->cvw_refcnt == -1);                 \
        (_c)->cvw_refcnt = 1;                           \
        cv_broadcast(&(_c)->cvw_waiter);                \
        mutex_exit(&(_c)->cvw_lock);                    \
}

#define CVW_DESTROY(_c) {                               \
        mutex_destroy(&(_c)->cvw_lock);                 \
        cv_destroy(&(_c)->cvw_waiter);                  \
}

#ifdef  __cplusplus
}
#endif

#endif  /* _SYS_CONDVAR_IMPL_H */