source: trunk/third/rpm/db/mutex/mut_tas.c @ 19079

/*-
 * See the file LICENSE for redistribution information.
 *
 * Copyright (c) 1996-2002
 *      Sleepycat Software.  All rights reserved.
 */

#include "db_config.h"

#ifndef lint
static const char revid[] = "Id: mut_tas.c,v 11.32 2002/05/07 18:42:21 bostic Exp ";
#endif /* not lint */

#ifndef NO_SYSTEM_INCLUDES
#include <sys/types.h>

#include <stdlib.h>
#include <string.h>
#include <unistd.h>
#endif

/*
 * This is where we load in the actual test-and-set mutex code.
 */
#define LOAD_ACTUAL_MUTEX_CODE
#include "db_int.h"

/*
 * __db_tas_mutex_init --
 *      Initialize a DB_MUTEX.
 *
 * PUBLIC: int __db_tas_mutex_init __P((DB_ENV *, DB_MUTEX *, u_int32_t));
 */
int
__db_tas_mutex_init(dbenv, mutexp, flags)
        DB_ENV *dbenv;
        DB_MUTEX *mutexp;
        u_int32_t flags;
{
        u_int32_t save;

        /* Check alignment. */
        DB_ASSERT(((db_alignp_t)mutexp & (MUTEX_ALIGN - 1)) == 0);

        /*
         * The only setting/checking of the MUTEX_MPOOL flags is in the mutex
         * mutex allocation code (__db_mutex_alloc/free).  Preserve only that
         * flag.  This is safe because even if this flag was never explicitly
         * set, but happened to be set in memory, it will never be checked or
         * acted upon.
         */
        save = F_ISSET(mutexp, MUTEX_MPOOL);
        memset(mutexp, 0, sizeof(*mutexp));
        F_SET(mutexp, save);

        /*
         * If this is a thread lock or the process has told us that there are
         * no other processes in the environment, use thread-only locks, they
         * are faster in some cases.
         *
         * This is where we decide to ignore locks we don't need to set -- if
         * the application isn't threaded, there aren't any threads to block.
         */
        if (LF_ISSET(MUTEX_THREAD) || F_ISSET(dbenv, DB_ENV_PRIVATE)) {
                if (!F_ISSET(dbenv, DB_ENV_THREAD)) {
                        F_SET(mutexp, MUTEX_IGNORE);
                        return (0);
                }
        }

        /* Initialize the lock. */
        if (MUTEX_INIT(&mutexp->tas))
                return (__os_get_errno());

        mutexp->spins = __os_spin(dbenv);
#ifdef HAVE_MUTEX_SYSTEM_RESOURCES
        mutexp->reg_off = INVALID_ROFF;
#endif
        F_SET(mutexp, MUTEX_INITED);

        return (0);
}

/*
 * __db_tas_mutex_lock
 *      Lock on a mutex, logically blocking if necessary.
 *
 * PUBLIC: int __db_tas_mutex_lock __P((DB_ENV *, DB_MUTEX *));
 */
int
__db_tas_mutex_lock(dbenv, mutexp)
        DB_ENV *dbenv;
        DB_MUTEX *mutexp;
{
        u_long ms;
        int nspins;

        if (F_ISSET(dbenv, DB_ENV_NOLOCKING) || F_ISSET(mutexp, MUTEX_IGNORE))
                return (0);

        ms = 1;

loop:   /* Attempt to acquire the resource for N spins. */
        for (nspins = mutexp->spins; nspins > 0; --nspins) {
#ifdef HAVE_MUTEX_HPPA_MSEM_INIT
relock:
#endif
                if (!MUTEX_SET(&mutexp->tas))
                        continue;
#ifdef HAVE_MUTEX_HPPA_MSEM_INIT
                /*
                 * HP semaphores are unlocked automatically when a holding
                 * process exits.  If the mutex appears to be locked
                 * (mutexp->locked != 0) but we got here, assume this has
                 * happened.  Stick our own pid into mutexp->locked and
                 * lock again.  (The default state of the mutexes used to
                 * block in __lock_get_internal is locked, so exiting with
                 * a locked mutex is reasonable behavior for a process that
                 * happened to initialize or use one of them.)
                 */
                if (mutexp->locked != 0) {
                        __os_id(&mutexp->locked);
                        goto relock;
                }
                /*
                 * If we make it here, locked == 0, the diagnostic won't fire,
                 * and we were really unlocked by someone calling the
                 * DB mutex unlock function.
                 */
#endif
#ifdef DIAGNOSTIC
                if (mutexp->locked != 0)
                        __db_err(dbenv,
                "__db_tas_mutex_lock: ERROR: lock currently in use: ID: %lu",
                            (u_long)mutexp->locked);
#endif
#if defined(DIAGNOSTIC) || defined(HAVE_MUTEX_HPPA_MSEM_INIT)
                __os_id(&mutexp->locked);
#endif
                if (ms == 1)
                        ++mutexp->mutex_set_nowait;
                else
                        ++mutexp->mutex_set_wait;
                return (0);
        }

        /* Yield the processor; wait 1ms initially, up to 1 second. */
        __os_yield(NULL, ms * USEC_PER_MS);
        if ((ms <<= 1) > MS_PER_SEC)
                ms = MS_PER_SEC;

        goto loop;
}

/*
 * __db_tas_mutex_unlock --
 *      Release a lock.
 *
 * PUBLIC: int __db_tas_mutex_unlock __P((DB_ENV *, DB_MUTEX *));
 */
int
__db_tas_mutex_unlock(dbenv, mutexp)
        DB_ENV *dbenv;
        DB_MUTEX *mutexp;
{
        if (F_ISSET(dbenv, DB_ENV_NOLOCKING) || F_ISSET(mutexp, MUTEX_IGNORE))
                return (0);

#ifdef DIAGNOSTIC
        if (!mutexp->locked)
                __db_err(dbenv,
                    "__db_tas_mutex_unlock: ERROR: lock already unlocked");
#endif
#if defined(DIAGNOSTIC) || defined(HAVE_MUTEX_HPPA_MSEM_INIT)
        mutexp->locked = 0;
#endif

        MUTEX_UNSET(&mutexp->tas);

        return (0);
}

/*
 * __db_tas_mutex_destroy --
 *      Destroy a DB_MUTEX.
 *
 * PUBLIC: int __db_tas_mutex_destroy __P((DB_MUTEX *));
 */
int
__db_tas_mutex_destroy(mutexp)
        DB_MUTEX *mutexp;
{
        if (F_ISSET(mutexp, MUTEX_IGNORE))
                return (0);

        MUTEX_DESTROY(&mutexp->tas);

        return (0);
}