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 <stdio.h>
  48 #include "libguile/_scm.h"
  49 #include "libguile/ports.h"
  50 #include "libguile/smob.h"
  51
  52 #include "libguile/validate.h"
  53 #include "libguile/arbiters.h"
  54
  55 \f
  56 /* {Arbiters}
  57  *
  58  * These procedures implement synchronization primitives.  Processors
  59  * with an atomic test-and-set instruction can use it here (and not
  60  * SCM_DEFER_INTS).
  61  */
  62
  63 static scm_bits_t scm_tc16_arbiter;
  64
  65
  66 #define SCM_ARB_LOCKED(arb)  ((SCM_CELL_WORD_0 (arb)) & (1L << 16))
  67 #define SCM_LOCK_ARB(arb)    (SCM_SET_CELL_WORD_0 ((arb), scm_tc16_arbiter | (1L << 16)));
  68 #define SCM_UNLOCK_ARB(arb)  (SCM_SET_CELL_WORD_0 ((arb), scm_tc16_arbiter));
  69
  70 static int
  71 arbiter_print (SCM exp, SCM port, scm_print_state *pstate)
  72 {
  73   scm_puts ("#<arbiter ", port);
  74   if (SCM_ARB_LOCKED (exp))
  75     scm_puts ("locked ", port);
  76   scm_iprin1 (SCM_PACK (SCM_SMOB_DATA (exp)), port, pstate);
  77   scm_putc ('>', port);
  78   return !0;
  79 }
  80
  81 SCM_DEFINE (scm_make_arbiter, "make-arbiter", 1, 0, 0,
  82             (SCM name),
  83             "Return an object of type arbiter and name @var{name}. Its\n"
  84             "state is initially unlocked.  Arbiters are a way to achieve\n"
  85             "process synchronization.")
  86 #define FUNC_NAME s_scm_make_arbiter
  87 {
  88   SCM_RETURN_NEWSMOB (scm_tc16_arbiter, SCM_UNPACK (name));
  89 }
  90 #undef FUNC_NAME
  91
  92 SCM_DEFINE (scm_try_arbiter, "try-arbiter", 1, 0, 0,
  93             (SCM arb),
  94             "Return @code{#t} and lock the arbiter @var{arb} if the arbiter\n"
  95             "was unlocked. Otherwise, return @code{#f}.")
  96 #define FUNC_NAME s_scm_try_arbiter
  97 {
  98   SCM_VALIDATE_SMOB (1, arb, arbiter);
  99   SCM_DEFER_INTS;
 100   if (SCM_ARB_LOCKED(arb))
 101     arb = SCM_BOOL_F;
 102   else
 103     {
 104       SCM_LOCK_ARB(arb);
 105       arb = SCM_BOOL_T;
 106     }
 107   SCM_ALLOW_INTS;
 108   return arb;
 109 }
 110 #undef FUNC_NAME
 111
 112
 113 SCM_DEFINE (scm_release_arbiter, "release-arbiter", 1, 0, 0,
 114             (SCM arb),
 115             "Return @code{#t} and unlock the arbiter @var{arb} if the\n"
 116             "arbiter was locked. Otherwise, return @code{#f}.")
 117 #define FUNC_NAME s_scm_release_arbiter
 118 {
 119   SCM_VALIDATE_SMOB (1, arb, arbiter);
 120   if (!SCM_ARB_LOCKED(arb))
 121     return SCM_BOOL_F;
 122   SCM_UNLOCK_ARB (arb);
 123   return SCM_BOOL_T;
 124 }
 125 #undef FUNC_NAME
 126
 127
 128
 129 void
 130 scm_init_arbiters ()
 131 {
 132   scm_tc16_arbiter = scm_make_smob_type ("arbiter", 0);
 133   scm_set_smob_mark (scm_tc16_arbiter, scm_markcdr);
 134   scm_set_smob_print (scm_tc16_arbiter, arbiter_print);
 135 #ifndef SCM_MAGIC_SNARFER
 136 #include "libguile/arbiters.x"
 137 #endif
 138 }
 139
 140 /*
 141   Local Variables:
 142   c-file-style: "gnu"
 143   End:
 144 */