(scm_setgroups): Enhance docstring, per doc/ref/posix.texi.

[bpt/guile.git] / libguile / arbiters.c

/*	Copyright (C) 1995,1996, 1997, 2000, 2001 Free Software Foundation, Inc.
 * 
 * This library is free software; you can redistribute it and/or
 * modify it under the terms of the GNU Lesser General Public
 * License as published by the Free Software Foundation; either
 * version 2.1 of the License, or (at your option) any later version.
 *
 * This library is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
 * Lesser General Public License for more details.
 *
 * You should have received a copy of the GNU Lesser General Public
 * License along with this library; if not, write to the Free Software
 * Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA
 */


\f

#include "libguile/_scm.h"
#include "libguile/ports.h"
#include "libguile/smob.h"

#include "libguile/validate.h"
#include "libguile/arbiters.h"

\f
/* {Arbiters}
 *
 * These procedures implement synchronization primitives.  Processors
 * with an atomic test-and-set instruction can use it here (and not
 * SCM_DEFER_INTS). 
 */

static scm_t_bits scm_tc16_arbiter;


#define SCM_ARB_LOCKED(arb)  ((SCM_CELL_WORD_0 (arb)) & (1L << 16))
#define SCM_LOCK_ARB(arb)    (SCM_SET_CELL_WORD_0 ((arb), scm_tc16_arbiter | (1L << 16)));
#define SCM_UNLOCK_ARB(arb)  (SCM_SET_CELL_WORD_0 ((arb), scm_tc16_arbiter));

static int 
arbiter_print (SCM exp, SCM port, scm_print_state *pstate)
{
  scm_puts ("#<arbiter ", port);
  if (SCM_ARB_LOCKED (exp))
    scm_puts ("locked ", port);
  scm_iprin1 (SCM_PACK (SCM_SMOB_DATA (exp)), port, pstate);
  scm_putc ('>', port);
  return !0;
}

SCM_DEFINE (scm_make_arbiter, "make-arbiter", 1, 0, 0, 
	    (SCM name),
	    "Return an object of type arbiter and name @var{name}. Its\n"
	    "state is initially unlocked.  Arbiters are a way to achieve\n"
	    "process synchronization.")
#define FUNC_NAME s_scm_make_arbiter
{
  SCM_RETURN_NEWSMOB (scm_tc16_arbiter, SCM_UNPACK (name));
}
#undef FUNC_NAME

SCM_DEFINE (scm_try_arbiter, "try-arbiter", 1, 0, 0, 
	    (SCM arb),
	    "Return @code{#t} and lock the arbiter @var{arb} if the arbiter\n"
	    "was unlocked. Otherwise, return @code{#f}.")
#define FUNC_NAME s_scm_try_arbiter
{
  SCM_VALIDATE_SMOB (1, arb, arbiter);
  SCM_DEFER_INTS;
  if (SCM_ARB_LOCKED(arb))
    arb = SCM_BOOL_F;
  else
    {
      SCM_LOCK_ARB(arb);
      arb = SCM_BOOL_T;
    }
  SCM_ALLOW_INTS;
  return arb;
}
#undef FUNC_NAME


SCM_DEFINE (scm_release_arbiter, "release-arbiter", 1, 0, 0, 
	    (SCM arb),
	    "Return @code{#t} and unlock the arbiter @var{arb} if the\n"
	    "arbiter was locked. Otherwise, return @code{#f}.")
#define FUNC_NAME s_scm_release_arbiter
{
  SCM_VALIDATE_SMOB (1, arb, arbiter);
  if (!SCM_ARB_LOCKED(arb))
    return SCM_BOOL_F;
  SCM_UNLOCK_ARB (arb);
  return SCM_BOOL_T;
}
#undef FUNC_NAME



void
scm_init_arbiters ()
{
  scm_tc16_arbiter = scm_make_smob_type ("arbiter", 0);
  scm_set_smob_mark (scm_tc16_arbiter, scm_markcdr);
  scm_set_smob_print (scm_tc16_arbiter, arbiter_print);
#include "libguile/arbiters.x"
}

/*
  Local Variables:
  c-file-style: "gnu"
  End:
*/