2006-02-01 Ludovic Courtès <ludovic.courtes@laas.fr>

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

/* Copyright (C) 1995,1996,1997,1998,2000,2001, 2003, 2004 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., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
 */


\f

#include <stdio.h>
#include "libguile/_scm.h"
#include "libguile/async.h"
#include "libguile/smob.h"
#include "libguile/alist.h"
#include "libguile/eval.h"
#include "libguile/eq.h"
#include "libguile/dynwind.h"
#include "libguile/backtrace.h"
#include "libguile/debug.h"
#include "libguile/continuations.h"
#include "libguile/stackchk.h"
#include "libguile/stacks.h"
#include "libguile/fluids.h"
#include "libguile/ports.h"
#include "libguile/lang.h"
#include "libguile/validate.h"
#include "libguile/throw.h"
#include "libguile/init.h"

\f
/* the jump buffer data structure */
static scm_t_bits tc16_jmpbuffer;

#define SCM_JMPBUFP(OBJ)	SCM_TYP16_PREDICATE (tc16_jmpbuffer, OBJ)

#define JBACTIVE(OBJ)		(SCM_CELL_WORD_0 (OBJ) & (1L << 16L))
#define ACTIVATEJB(x)	\
  (SCM_SET_CELL_WORD_0 ((x), (SCM_CELL_WORD_0 (x) | (1L << 16L))))
#define DEACTIVATEJB(x) \
  (SCM_SET_CELL_WORD_0 ((x), (SCM_CELL_WORD_0 (x) & ~(1L << 16L))))

#define JBJMPBUF(OBJ)           ((jmp_buf *) SCM_CELL_WORD_1 (OBJ))
#define SETJBJMPBUF(x, v)        (SCM_SET_CELL_WORD_1 ((x), (scm_t_bits) (v)))
#define SCM_JBDFRAME(x)         ((scm_t_debug_frame *) SCM_CELL_WORD_2 (x))
#define SCM_SETJBDFRAME(x, v)    (SCM_SET_CELL_WORD_2 ((x), (scm_t_bits) (v)))

static int
jmpbuffer_print (SCM exp, SCM port, scm_print_state *pstate SCM_UNUSED)
{
  scm_puts ("#<jmpbuffer ", port);
  scm_puts (JBACTIVE(exp) ? "(active) " : "(inactive) ", port);
  scm_uintprint((scm_t_bits) JBJMPBUF (exp), 16, port);
  scm_putc ('>', port);
  return 1 ;
}

static SCM
make_jmpbuf (void)
{
  SCM answer;
  SCM_CRITICAL_SECTION_START;
  {
    SCM_NEWSMOB2 (answer, tc16_jmpbuffer, 0, 0);
    SETJBJMPBUF(answer, (jmp_buf *)0);
    DEACTIVATEJB(answer);
  }
  SCM_CRITICAL_SECTION_END;
  return answer;
}

\f
/* scm_internal_catch (the guts of catch) */

struct jmp_buf_and_retval	/* use only on the stack, in scm_catch */
{
  jmp_buf buf;			/* must be first */
  SCM throw_tag;
  SCM retval;
};


/* scm_internal_catch is the guts of catch.  It handles all the
   mechanics of setting up a catch target, invoking the catch body,
   and perhaps invoking the handler if the body does a throw.

   The function is designed to be usable from C code, but is general
   enough to implement all the semantics Guile Scheme expects from
   throw.

   TAG is the catch tag.  Typically, this is a symbol, but this
   function doesn't actually care about that.

   BODY is a pointer to a C function which runs the body of the catch;
   this is the code you can throw from.  We call it like this:
      BODY (BODY_DATA)
   where:
      BODY_DATA is just the BODY_DATA argument we received; we pass it
	 through to BODY as its first argument.  The caller can make
	 BODY_DATA point to anything useful that BODY might need.

   HANDLER is a pointer to a C function to deal with a throw to TAG,
   should one occur.  We call it like this:
      HANDLER (HANDLER_DATA, THROWN_TAG, THROW_ARGS)
   where
      HANDLER_DATA is the HANDLER_DATA argument we recevied; it's the
         same idea as BODY_DATA above.
      THROWN_TAG is the tag that the user threw to; usually this is
         TAG, but it could be something else if TAG was #t (i.e., a
         catch-all), or the user threw to a jmpbuf.
      THROW_ARGS is the list of arguments the user passed to the THROW
         function, after the tag.

   BODY_DATA is just a pointer we pass through to BODY.  HANDLER_DATA
   is just a pointer we pass through to HANDLER.  We don't actually
   use either of those pointers otherwise ourselves.  The idea is
   that, if our caller wants to communicate something to BODY or
   HANDLER, it can pass a pointer to it as MUMBLE_DATA, which BODY and
   HANDLER can then use.  Think of it as a way to make BODY and
   HANDLER closures, not just functions; MUMBLE_DATA points to the
   enclosed variables.

   Of course, it's up to the caller to make sure that any data a
   MUMBLE_DATA needs is protected from GC.  A common way to do this is
   to make MUMBLE_DATA a pointer to data stored in an automatic
   structure variable; since the collector must scan the stack for
   references anyway, this assures that any references in MUMBLE_DATA
   will be found.  */

SCM
scm_internal_catch (SCM tag, scm_t_catch_body body, void *body_data, scm_t_catch_handler handler, void *handler_data)
{
  struct jmp_buf_and_retval jbr;
  SCM jmpbuf;
  SCM answer;

  jmpbuf = make_jmpbuf ();
  answer = SCM_EOL;
  scm_i_set_dynwinds (scm_acons (tag, jmpbuf, scm_i_dynwinds ()));
  SETJBJMPBUF(jmpbuf, &jbr.buf);
  SCM_SETJBDFRAME(jmpbuf, scm_i_last_debug_frame ());
  if (setjmp (jbr.buf))
    {
      SCM throw_tag;
      SCM throw_args;

#ifdef STACK_CHECKING
      scm_stack_checking_enabled_p = SCM_STACK_CHECKING_P;
#endif
      SCM_CRITICAL_SECTION_START;
      DEACTIVATEJB (jmpbuf);
      scm_i_set_dynwinds (SCM_CDR (scm_i_dynwinds ()));
      SCM_CRITICAL_SECTION_END;
      throw_args = jbr.retval;
      throw_tag = jbr.throw_tag;
      jbr.throw_tag = SCM_EOL;
      jbr.retval = SCM_EOL;
      answer = handler (handler_data, throw_tag, throw_args);
    }
  else
    {
      ACTIVATEJB (jmpbuf);
      answer = body (body_data);
      SCM_CRITICAL_SECTION_START;
      DEACTIVATEJB (jmpbuf);
      scm_i_set_dynwinds (SCM_CDR (scm_i_dynwinds ()));
      SCM_CRITICAL_SECTION_END;
    }
  return answer;
}


\f
/* scm_internal_lazy_catch (the guts of lazy catching) */

/* The smob tag for lazy_catch smobs.  */
static scm_t_bits tc16_lazy_catch;

/* This is the structure we put on the wind list for a lazy catch.  It
   stores the handler function to call, and the data pointer to pass
   through to it.  It's not a Scheme closure, but it is a function
   with data, so the term "closure" is appropriate in its broader
   sense.

   (We don't need anything like this in the "eager" catch code,
   because the same C frame runs both the body and the handler.)  */
struct lazy_catch {
  scm_t_catch_handler handler;
  void *handler_data;
};

/* Strictly speaking, we could just pass a zero for our print
   function, because we don't need to print them.  They should never
   appear in normal data structures, only in the wind list.  However,
   it might be nice for debugging someday... */
static int
lazy_catch_print (SCM closure, SCM port, scm_print_state *pstate SCM_UNUSED)
{
  struct lazy_catch *c = (struct lazy_catch *) SCM_CELL_WORD_1 (closure);
  char buf[200];

  sprintf (buf, "#<lazy-catch 0x%lx 0x%lx>",
	   (long) c->handler, (long) c->handler_data);
  scm_puts (buf, port);

  return 1;
}


/* Given a pointer to a lazy catch structure, return a smob for it,