libguile/arbiters.c

   1 /*      Copyright (C) 1995,1996, 1997, 2000 Free Software Foundation, Inc.
   2  *
   3  * This program is free software; you can redistribute it and/or modify
   4  * it under the terms of the GNU General Public License as published by
   5  * the Free Software Foundation; either version 2, or (at your option)
   6  * any later version.
   7  *
   8  * This program is distributed in the hope that it will be useful,
   9  * but WITHOUT ANY WARRANTY; without even the implied warranty of
  10  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  11  * GNU General Public License for more details.
  12  *
  13  * You should have received a copy of the GNU General Public License
  14  * along with this software; see the file COPYING.  If not, write to
  15  * the Free Software Foundation, Inc., 59 Temple Place, Suite 330,
  16  * Boston, MA 02111-1307 USA
  17  *
  18  * As a special exception, the Free Software Foundation gives permission
  19  * for additional uses of the text contained in its release of GUILE.
  20  *
  21  * The exception is that, if you link the GUILE library with other files
  22  * to produce an executable, this does not by itself cause the
  23  * resulting executable to be covered by the GNU General Public License.
  24  * Your use of that executable is in no way restricted on account of
  25  * linking the GUILE library code into it.
  26  *
  27  * This exception does not however invalidate any other reasons why
  28  * the executable file might be covered by the GNU General Public License.
  29  *
  30  * This exception applies only to the code released by the
  31  * Free Software Foundation under the name GUILE.  If you copy
  32  * code from other Free Software Foundation releases into a copy of
  33  * GUILE, as the General Public License permits, the exception does
  34  * not apply to the code that you add in this way.  To avoid misleading
  35  * anyone as to the status of such modified files, you must delete
  36  * this exception notice from them.
  37  *
  38  * If you write modifications of your own for GUILE, it is your choice
  39  * whether to permit this exception to apply to your modifications.
  40  * If you do not wish that, delete this exception notice.  */
  41
  42 /* Software engineering face-lift by Greg J. Badros, 11-Dec-1999,
  43    gjb@cs.washington.edu, http://www.cs.washington.edu/homes/gjb */
  44
  45 \f
  46
  47 #include "libguile/_scm.h"
  48 #include "libguile/ports.h"
  49 #include "libguile/smob.h"
  50
  51 #include "libguile/validate.h"
  52 #include "libguile/arbiters.h"
  53
  54 \f
  55 /* {Arbiters}
  56  *
  57  * These procedures implement synchronization primitives.  Processors
  58  * with an atomic test-and-set instruction can use it here (and not
  59  * SCM_DEFER_INTS).
  60  */
  61
  62 static scm_bits_t scm_tc16_arbiter;
  63
  64
  65 #define SCM_ARB_LOCKED(arb)  ((SCM_CELL_WORD_0 (arb)) & (1L << 16))
  66 #define SCM_LOCK_ARB(arb)    (SCM_SET_CELL_WORD_0 ((arb), scm_tc16_arbiter | (1L << 16)));
  67 #define SCM_UNLOCK_ARB(arb)  (SCM_SET_CELL_WORD_0 ((arb), scm_tc16_arbiter));
  68
  69 static int
  70 arbiter_print (SCM exp, SCM port, scm_print_state *pstate)
  71 {
  72   scm_puts ("#<arbiter ", port);
  73   if (SCM_ARB_LOCKED (exp))
  74     scm_puts ("locked ", port);
  75   scm_iprin1 (SCM_PACK (SCM_SMOB_DATA (exp)), port, pstate);
  76   scm_putc ('>', port);
  77   return !0;
  78 }
  79
  80 SCM_DEFINE (scm_make_arbiter, "make-arbiter", 1, 0, 0,
  81             (SCM name),
  82             "Return an object of type arbiter and name @var{name}. Its\n"
  83             "state is initially unlocked.  Arbiters are a way to achieve\n"
  84             "process synchronization.")
  85 #define FUNC_NAME s_scm_make_arbiter
  86 {
  87   SCM_RETURN_NEWSMOB (scm_tc16_arbiter, SCM_UNPACK (name));
  88 }
  89 #undef FUNC_NAME
  90
  91 SCM_DEFINE (scm_try_arbiter, "try-arbiter", 1, 0, 0,
  92             (SCM arb),
  93             "Return @code{#t} and lock the arbiter @var{arb} if the arbiter\n"
  94             "was unlocked. Otherwise, return @code{#f}.")
  95 #define FUNC_NAME s_scm_try_arbiter
  96 {
  97   SCM_VALIDATE_SMOB (1, arb, arbiter);
  98   SCM_DEFER_INTS;
  99   if (SCM_ARB_LOCKED(arb))
 100     arb = SCM_BOOL_F;
 101   else
 102     {
 103       SCM_LOCK_ARB(arb);
 104       arb = SCM_BOOL_T;
 105     }
 106   SCM_ALLOW_INTS;
 107   return arb;
 108 }
 109 #undef FUNC_NAME
 110
 111
 112 SCM_DEFINE (scm_release_arbiter, "release-arbiter", 1, 0, 0,
 113             (SCM arb),
 114             "Return @code{#t} and unlock the arbiter @var{arb} if the\n"
 115             "arbiter was locked. Otherwise, return @code{#f}.")
 116 #define FUNC_NAME s_scm_release_arbiter
 117 {
 118   SCM_VALIDATE_SMOB (1, arb, arbiter);
 119   if (!SCM_ARB_LOCKED(arb))
 120     return SCM_BOOL_F;
 121   SCM_UNLOCK_ARB (arb);
 122   return SCM_BOOL_T;
 123 }
 124 #undef FUNC_NAME
 125
 126
 127
 128 void
 129 scm_init_arbiters ()
 130 {
 131   scm_tc16_arbiter = scm_make_smob_type ("arbiter", 0);
 132   scm_set_smob_mark (scm_tc16_arbiter, scm_markcdr);
 133   scm_set_smob_print (scm_tc16_arbiter, arbiter_print);
 134 #ifndef SCM_MAGIC_SNARFER
 135 #include "libguile/arbiters.x"
 136 #endif
 137 }
 138
 139 /*
 140   Local Variables:
 141   c-file-style: "gnu"
 142   End:
 143 */