common/os/rwstlock.c

	rwstlock.c revision 7c478bd95313f5f23a4c958a745db2134aa03244
/*
 * CDDL HEADER START
 *
 * The contents of this file are subject to the terms of the
 * Common Development and Distribution License, Version 1.0 only
 * (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 2005 Sun Microsystems, Inc.  All rights reserved.
 * Use is subject to license terms.
 */

#pragma ident   "%Z%%M% %I% %E% SMI"

#include <sys/rwstlock.h>
#include <sys/errno.h>
#include <sys/debug.h>
#include <sys/lockstat.h>
#include <sys/sysmacros.h>
#include <sys/condvar_impl.h>

/*
 * Alternate rwlock that is interruptible and can be released by a thread
 * other than the one that acquired the lock.
 *
 * There is no priority inheritance mechanism for these locks.
 * Writers have priority over readers, so reader starvation is possible.
 */

/*
 * Common code to grab a lock.  There are three cases:
 *
 * (1) If RWST_TRYENTER is set, we try the lock without blocking.
 *     In this case we return 1 on success, 0 on failure.
 *
 * (2) If RWST_SIG is set, we block interruptibly until we get the lock.
 *     In this case we return 0 on success, EINTR if we're interrupted.
 *
 * (3) If neither flag is set, we block uninterruptibly until we get the lock.
 *     In this case we return 0 (we always succeed).
 */
static int
rwst_enter_common(rwstlock_t *l, krw_t rw, int flags)
{
    hrtime_t sleep_time;
    int writer;
    intptr_t readers;

    mutex_enter(&l->rwst_lock);
    if (rw == RW_READER) {
        while (RWST_WRITE_HELD(l) || RWST_WRITE_WANTED(l)) {

            if (flags & RWST_TRYENTER) {
                mutex_exit(&l->rwst_lock);
                return (0);
            }
            if (panicstr)
                return (0);

            if (RWST_WRITE_HELD(l)) {
                writer = 1;
                readers = 0;
            } else {
                writer = 0;
                readers = l->rwst_count;
            }
            sleep_time = -gethrtime();
            if (!RWST_READ_WAIT(l, flags)) {
                mutex_exit(&l->rwst_lock);
                return (EINTR);
            }
            sleep_time += gethrtime();
            LOCKSTAT_RECORD4(LS_RW_ENTER_BLOCK, l, sleep_time, rw,
                writer, readers);
        }
        RWST_READ_ENTER(l);
        LOCKSTAT_RECORD(LS_RW_ENTER_ACQUIRE, l, rw);
    } else {
        ASSERT(rw == RW_WRITER);
        while (RWST_HELD(l)) {
            if (flags & RWST_TRYENTER) {
                mutex_exit(&l->rwst_lock);
                return (0);
            }
            if (panicstr)
                return (0);
            if (RWST_WRITE_HELD(l)) {
                writer = 1;
                readers = 0;
            } else {
                writer = 0;
                readers = l->rwst_count;
            }
            sleep_time = -gethrtime();
            if (!RWST_WRITE_WAIT(l, flags)) {
                if (!RWST_WRITE_HELD(l) &&
                    !RWST_WRITE_WANTED(l))
                    RWST_READ_WAKE_ALL(l);
                mutex_exit(&l->rwst_lock);
                return (EINTR);
            }
            sleep_time += gethrtime();
            LOCKSTAT_RECORD4(LS_RW_ENTER_BLOCK, l, sleep_time, rw,
                writer, readers);
        }
        RWST_WRITE_ENTER(l);
        LOCKSTAT_RECORD(LS_RW_ENTER_ACQUIRE, l, rw);
    }
    mutex_exit(&l->rwst_lock);
    return (flags & RWST_TRYENTER);
}

void
rwst_exit(rwstlock_t *l)
{
    mutex_enter(&l->rwst_lock);
    if (RWST_WRITE_HELD(l)) {
        LOCKSTAT_RECORD(LS_RW_EXIT_RELEASE, l, RW_WRITER);
        RWST_WRITE_EXIT(l);
    } else {
        ASSERT(RWST_READ_HELD(l));
        LOCKSTAT_RECORD(LS_RW_EXIT_RELEASE, l, RW_READER);
        RWST_READ_EXIT(l);
    }
    if (!RWST_WRITE_WANTED(l))
        RWST_READ_WAKE_ALL(l);
    else if (!RWST_HELD(l))
        RWST_WRITE_WAKE_ONE(l);
    mutex_exit(&l->rwst_lock);
}

void
rwst_enter(rwstlock_t *l, krw_t rw)
{
    (void) rwst_enter_common(l, rw, 0);
}

int
rwst_enter_sig(rwstlock_t *l, krw_t rw)
{
    return (rwst_enter_common(l, rw, RWST_SIG));
}

int
rwst_tryenter(rwstlock_t *l, krw_t rw)
{
    return (rwst_enter_common(l, rw, RWST_TRYENTER));
}

int
rwst_lock_held(rwstlock_t *l, krw_t rw)
{
    if (rw == RW_READER)
        return (RWST_READ_HELD(l));
    ASSERT(rw == RW_WRITER);
    return (RWST_WRITE_OWNER(l));
}

/*ARGSUSED*/
void
rwst_init(rwstlock_t *l, char *name, krw_type_t krw_t, void *arg)
{
    l->rwst_count = 0;
    mutex_init(&l->rwst_lock, NULL, MUTEX_DEFAULT, NULL);
    cv_init(&l->rwst_rcv, NULL, CV_DEFAULT, NULL);
    cv_init(&l->rwst_wcv, NULL, CV_DEFAULT, NULL);
}

void
rwst_destroy(rwstlock_t *l)
{
    ASSERT(l->rwst_count == 0);
    mutex_destroy(&l->rwst_lock);
    cv_destroy(&l->rwst_rcv);
    cv_destroy(&l->rwst_wcv);
}

struct _kthread *
rwst_owner(rwstlock_t *l)
{
    return (RWST_OWNER(l));
}