db2/os/os_spin.c

   1 /*-
   2  * See the file LICENSE for redistribution information.
   3  *
   4  * Copyright (c) 1997, 1998
   5  *      Sleepycat Software.  All rights reserved.
   6  */
   7
   8 #include "config.h"
   9
  10 #ifndef lint
  11 static const char sccsid[] = "@(#)os_spin.c     10.7 (Sleepycat) 5/20/98";
  12 #endif /* not lint */
  13
  14 #ifndef NO_SYSTEM_INCLUDES
  15 #include <sys/types.h>
  16
  17 #include <limits.h>
  18 #include <unistd.h>
  19 #endif
  20
  21 #include "db_int.h"
  22
  23 /*
  24  * __os_spin --
  25  *      Return the number of default spins before blocking.
  26  *
  27  * PUBLIC: int __os_spin __P((void));
  28  */
  29 int
  30 __os_spin()
  31 {
  32         static long sys_val;
  33
  34         /* If the application specified the spins, use its value. */
  35         if (DB_GLOBAL(db_tsl_spins) != 0)
  36                 return (DB_GLOBAL(db_tsl_spins));
  37
  38         /* If we've already figured this out, return the value. */
  39         if (sys_val != 0)
  40                 return (sys_val);
  41
  42         /*
  43          * XXX
  44          * Solaris and Linux use _SC_NPROCESSORS_ONLN to return the number of
  45          * online processors.  We don't want to repeatedly call sysconf because
  46          * it's quite expensive (requiring multiple filesystem accesses) under
  47          * Debian Linux.
  48          *
  49          * Spin 50 times per processor -- we have anecdotal evidence that this
  50          * is a reasonable value.
  51          */
  52 #if defined(HAVE_SYSCONF) && defined(_SC_NPROCESSORS_ONLN)
  53         if ((sys_val = sysconf(_SC_NPROCESSORS_ONLN)) > 1)
  54                 sys_val *= 50;
  55         else
  56                 sys_val = 1;
  57 #else
  58         sys_val = 1;
  59 #endif
  60         return (sys_val);
  61 }