os_spin.c

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/*-
 * See the file LICENSE for redistribution information.
 *
 * Copyright (c) 1997, 1998, 1999, 2000
 *      Sleepycat Software.  All rights reserved.
 */

#include "config.h"

#ifndef lint
static const char revid[] = "$Id: os__spin_8c-source.html,v 1.1 2008/06/08 10:21:31 sebdiaz Exp $";
#endif /* not lint */

#ifndef NO_SYSTEM_INCLUDES
#include <sys/types.h>
#if defined(HAVE_PSTAT_GETDYNAMIC)
#include <sys/pstat.h>
#endif

#include <limits.h>
#include <unistd.h>
#endif

#include "db_int.h"
#include "os_jump.h"

#if defined(HAVE_PSTAT_GETDYNAMIC)
/*
 * __os_pstat_getdynamic --
 *      HP/UX.
 */
static int
__os_pstat_getdynamic()
{
        struct pst_dynamic psd;

        return (pstat_getdynamic(&psd,
            sizeof(psd), (size_t)1, 0) == -1 ? 1 : psd.psd_proc_cnt);
}
#endif

#if defined(HAVE_SYSCONF) && defined(_SC_NPROCESSORS_ONLN)
/*
 * __os_sysconf --
 *      Solaris, Linux.
 */
static int
__os_sysconf()
{
        int nproc;

        return ((nproc = sysconf(_SC_NPROCESSORS_ONLN)) > 1 ? nproc : 1);
}
#endif

/*
 * CDB___os_spin --
 *      Return the number of default spins before blocking.
 *
 * PUBLIC: int CDB___os_spin __P((void));
 */
int
CDB___os_spin()
{
        /*
         * If the application specified a value or we've already figured it
         * out, return it.
         *
         * XXX
         * We don't want to repeatedly call the underlying function because
         * it can be expensive (e.g., requiring multiple filesystem accesses
         * under Debian Linux).
         */
        if (DB_GLOBAL(db_tas_spins) != 0)
                return (DB_GLOBAL(db_tas_spins));

        DB_GLOBAL(db_tas_spins) = 1;
#if defined(HAVE_PSTAT_GETDYNAMIC)
        DB_GLOBAL(db_tas_spins) = __os_pstat_getdynamic();
#endif
#if defined(HAVE_SYSCONF) && defined(_SC_NPROCESSORS_ONLN)
        DB_GLOBAL(db_tas_spins) = __os_sysconf();
#endif

        /*
         * Spin 50 times per processor, we have anecdotal evidence that this
         * is a reasonable value.
         */
        if (DB_GLOBAL(db_tas_spins) != 1)
                DB_GLOBAL(db_tas_spins) *= 50;

        return (DB_GLOBAL(db_tas_spins));
}

/*
 * CDB___os_yield --
 *      Yield the processor.
 *
 * PUBLIC: void CDB___os_yield __P((DB_ENV*, u_long));
 */
void
CDB___os_yield(dbenv, usecs)
        DB_ENV *dbenv;
        u_long usecs;
{
        if (CDB___db_jump.j_yield != NULL && CDB___db_jump.j_yield() == 0)
                return;
        CDB___os_sleep(dbenv, 0, usecs);
}

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