db/os/os_spin.c

	os_spin.c revision 7c478bd95313f5f23a4c958a745db2134aa03244
/*-
 * See the file LICENSE for redistribution information.
 *
 * Copyright (c) 1997, 1998
 *  Sleepycat Software.  All rights reserved.
 */

#include "config.h"

#ifndef lint
static const char sccsid[] = "@(#)os_spin.c 10.10 (Sleepycat) 10/12/98";
#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

/*
 * __os_spin --
 *  Return the number of default spins before blocking.
 *
 * PUBLIC: int __os_spin __P((void));
 */
int
__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_tsl_spins) != 0)
        return (DB_GLOBAL(db_tsl_spins));

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

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

    return (DB_GLOBAL(db_tsl_spins));
}

/*
 * __os_yield --
 *  Yield the processor.
 *
 * PUBLIC: void __os_yield __P((u_long));
 */
void
__os_yield(usecs)
    u_long usecs;
{
    if (__db_jump.j_yield != NULL && __db_jump.j_yield() == 0)
        return;
    __os_sleep(0, usecs);
}