guile/libguile/scmsigs.c

/* Copyright (C) 1995,1996,1997,1998,1999,2000,2001 Free Software Foundation, Inc.
 *
 * This program is free software; you can redistribute it and/or modify
 * it under the terms of the GNU General Public License as published by
 * the Free Software Foundation; either version 2, or (at your option)
 * any later version.
 *
 * This program 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 General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License
 * along with this software; see the file COPYING.  If not, write to
 * the Free Software Foundation, Inc., 59 Temple Place, Suite 330,
 * Boston, MA 02111-1307 USA
 *
 * As a special exception, the Free Software Foundation gives permission
 * for additional uses of the text contained in its release of GUILE.
 *
 * The exception is that, if you link the GUILE library with other files
 * to produce an executable, this does not by itself cause the
 * resulting executable to be covered by the GNU General Public License.
 * Your use of that executable is in no way restricted on account of
 * linking the GUILE library code into it.
 *
 * This exception does not however invalidate any other reasons why
 * the executable file might be covered by the GNU General Public License.
 *
 * This exception applies only to the code released by the
 * Free Software Foundation under the name GUILE.  If you copy
 * code from other Free Software Foundation releases into a copy of
 * GUILE, as the General Public License permits, the exception does
 * not apply to the code that you add in this way.  To avoid misleading
 * anyone as to the status of such modified files, you must delete
 * this exception notice from them.
 *
 * If you write modifications of your own for GUILE, it is your choice
 * whether to permit this exception to apply to your modifications.
 * If you do not wish that, delete this exception notice.  */

/* Software engineering face-lift by Greg J. Badros, 11-Dec-1999,
   gjb@cs.washington.edu, http://www.cs.washington.edu/homes/gjb */



#include <signal.h>
#include <errno.h>

#include "libguile/_scm.h"

#include "libguile/async.h"
#include "libguile/eval.h"
#include "libguile/vectors.h"

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

#ifdef HAVE_UNISTD_H
#include <unistd.h>
#endif

/* The thread system has its own sleep and usleep functions.  */
#ifndef USE_THREADS

#if defined(MISSING_SLEEP_DECL)
int sleep ();
#endif

#if defined(HAVE_USLEEP) && defined(MISSING_USLEEP_DECL)
int usleep ();
#endif

#endif



/* SIGRETTYPE is the type that signal handlers return.  See <signal.h> */

#ifdef RETSIGTYPE
# define SIGRETTYPE RETSIGTYPE
#else
# ifdef STDC_HEADERS
#  define SIGRETTYPE void
# else
#  define SIGRETTYPE int
# endif
#endif



/* take_signal is installed as the C signal handler whenever a Scheme
   handler is set.  when a signal arrives, take_signal marks the corresponding
   element of got_signal and marks signal_async.  the thunk in signal_async
   (sys_deliver_signals) will be run at the next opportunity, outside a
   critical section. sys_deliver_signals runs each Scheme handler for
   which got_signal is set.  */

static SCM signal_async;

static char got_signal[NSIG];

/* a Scheme vector of handler procedures.  */
static SCM *signal_handlers;

/* saves the original C handlers, when a new handler is installed.
   set to SIG_ERR if the original handler is installed.  */
#ifdef HAVE_SIGACTION
static struct sigaction orig_handlers[NSIG];
#else
static SIGRETTYPE (*orig_handlers[NSIG])(int);
#endif

static SIGRETTYPE
take_signal (int signum)
{
  int saved_errno = errno;
  SCM ignored;

  if (!scm_ints_disabled)
    {
      /* For reasons of speed, the SCM_NEWCELL macro doesn't defer
	 interrupts.  Instead, it first sets its argument to point to
	 the first cell in the list, and then advances the freelist
	 pointer to the next cell.  Now, if this procedure is
	 interrupted, the only anomalous state possible is to have
	 both SCM_NEWCELL's argument and scm_freelist pointing to the
	 same cell.  To deal with this case, we always throw away the
	 first cell in scm_freelist here.

	 At least, that's the theory.  I'm not convinced that that's
	 the only anomalous path we need to worry about.  */
      SCM_NEWCELL (ignored);
    }
  got_signal[signum] = 1;
#if HAVE_SIGACTION
  /* unblock the signal before the scheme handler gets to run, since
     it may use longjmp to escape (i.e., throw an exception).  */
  {
    sigset_t set;
    sigemptyset (&set);
    sigaddset (&set, signum);
    sigprocmask (SIG_UNBLOCK, &set, NULL);
  }
#endif
  scm_system_async_mark (signal_async);
  errno = saved_errno;
}

static SCM
sys_deliver_signals (void)
{
  int i;

  for (i = 0; i < NSIG; i++)
    {
      if (got_signal[i])
	{
	  /* The flag is reset before calling the handler in case the
	     handler doesn't return.  If the handler doesn't return
	     but leaves other signals flagged, they their handlers
	     will be applied some time later when the async is checked
	     again.  It would probably be better to reset the flags
	     after doing a longjmp.  */
	  got_signal[i] = 0;
#ifndef HAVE_SIGACTION
	  signal (i, take_signal);
#endif
	  scm_apply (SCM_VELTS (*signal_handlers)[i],
		     SCM_LIST1 (SCM_MAKINUM (i)),
		     SCM_EOL);
	}
    }
  return SCM_UNSPECIFIED;
}

/* user interface for installation of signal handlers.  */
SCM_DEFINE (scm_sigaction, "sigaction", 1, 2, 0,
           (SCM signum, SCM handler, SCM flags),
	    "Install or report the signal handler for a specified signal.\n\n"
	    "@var{signum} is the signal number, which can be specified using the value\n"
	    "of variables such as @code{SIGINT}.\n\n"
	    "If @var{action} is omitted, @code{sigaction} returns a pair: the\n"
	    "CAR is the current\n"
	    "signal hander, which will be either an integer with the value @code{SIG_DFL}\n"
	    "(default action) or @code{SIG_IGN} (ignore), or the Scheme procedure which\n"
	    "handles the signal, or @code{#f} if a non-Scheme procedure handles the\n"
	    "signal.  The CDR contains the current @code{sigaction} flags for the handler.\n\n"
	    "If @var{action} is provided, it is installed as the new handler for\n"
	    "@var{signum}.  @var{action} can be a Scheme procedure taking one\n"
	    "argument, or the value of @code{SIG_DFL} (default action) or\n"
	    "@code{SIG_IGN} (ignore), or @code{#f} to restore whatever signal handler\n"
	    "was installed before @code{sigaction} was first used.  Flags can\n"
	    "optionally be specified for the new handler (@code{SA_RESTART} will\n"
	    "always be added if it's available and the system is using restartable\n"
	    "system calls.)  The return value is a pair with information about the\n"
	    "old handler as described above.\n\n"
	    "This interface does not provide access to the \"signal blocking\"\n"
	    "facility.  Maybe this is not needed, since the thread support may\n"
	    "provide solutions to the problem of consistent access to data\n"
	    "structures.")
#define FUNC_NAME s_scm_sigaction
{
  int csig;
#ifdef HAVE_SIGACTION
  struct sigaction action;
  struct sigaction old_action;
#else
  SIGRETTYPE (* chandler) (int);
  SIGRETTYPE (* old_chandler) (int);
#endif
  int query_only = 0;
  int save_handler = 0;
  SCM *scheme_handlers = SCM_VELTS (*signal_handlers);
  SCM old_handler;

  SCM_VALIDATE_INUM_COPY (1,signum,csig);
#if defined(HAVE_SIGACTION)
#if defined(SA_RESTART) && defined(HAVE_RESTARTABLE_SYSCALLS)
  /* don't allow SA_RESTART to be omitted if HAVE_RESTARTABLE_SYSCALLS
     is defined, since libguile would be likely to produce spurious
     EINTR errors.  */
  action.sa_flags = SA_RESTART;
#else
  action.sa_flags = 0;
#endif
  if (!SCM_UNBNDP (flags))
    {
      SCM_VALIDATE_INUM (3,flags);
      action.sa_flags |= SCM_INUM (flags);
    }
  sigemptyset (&action.sa_mask);
#endif
  SCM_DEFER_INTS;
  old_handler = scheme_handlers[csig];
  if (SCM_UNBNDP (handler))
    query_only = 1;
  else if (SCM_EQ_P (scm_integer_p (handler), SCM_BOOL_T))
    {
      if (SCM_NUM2LONG (2, handler) == (long) SIG_DFL
	  || SCM_NUM2LONG (2, handler) == (long) SIG_IGN)
	{
#ifdef HAVE_SIGACTION
	  action.sa_handler = (SIGRETTYPE (*) (int)) SCM_INUM (handler);
#else
	  chandler = (SIGRETTYPE (*) (int)) SCM_INUM (handler);
#endif
	  scheme_handlers[csig] = SCM_BOOL_F;
	}
      else
	SCM_OUT_OF_RANGE (2, handler);
    }
  else if (SCM_FALSEP (handler))
    {
      /* restore the default handler.  */
#ifdef HAVE_SIGACTION
      if (orig_handlers[csig].sa_handler == SIG_ERR)
	query_only = 1;
      else
	{
	  action = orig_handlers[csig];
	  orig_handlers[csig].sa_handler = SIG_ERR;
	  scheme_handlers[csig] = SCM_BOOL_F;
	}
#else
      if (orig_handlers[csig] == SIG_ERR)
	query_only = 1;
      else
	{
	  chandler = orig_handlers[csig];
	  orig_handlers[csig] = SIG_ERR;
	  scheme_handlers[csig] = SCM_BOOL_F;
	}
#endif
    }
  else
    {
      SCM_VALIDATE_NIM (2,handler);
#ifdef HAVE_SIGACTION
      action.sa_handler = take_signal;
      if (orig_handlers[csig].sa_handler == SIG_ERR)
	save_handler = 1;
#else
      chandler = take_signal;
      if (orig_handlers[csig] == SIG_ERR)
	save_handler = 1;
#endif
      scheme_handlers[csig] = handler;
    }

  /* XXX - Silently ignore setting handlers for `program error signals'
     because they can't currently be handled by Scheme code.
  */

  switch (csig)
    {
      /* This list of program error signals is from the GNU Libc
         Reference Manual */
    case SIGFPE:
    case SIGILL:
    case SIGSEGV:
    case SIGBUS:
    case SIGABRT:
#if defined(SIGIOT) && (SIGIOT != SIGABRT)
    case SIGIOT:
#endif
    case SIGTRAP:
#ifdef SIGEMT
    case SIGEMT:
#endif
#ifdef SIGSYS
    case SIGSYS:
#endif
      query_only = 1;
    }

#ifdef HAVE_SIGACTION
  if (query_only)
    {
      if (sigaction (csig, 0, &old_action) == -1)
	SCM_SYSERROR;
    }
  else
    {
      if (sigaction (csig, &action , &old_action) == -1)
	SCM_SYSERROR;
      if (save_handler)
	orig_handlers[csig] = old_action;
    }
  if (old_action.sa_handler == SIG_DFL || old_action.sa_handler == SIG_IGN)
    old_handler = scm_long2num ((long) old_action.sa_handler);
  SCM_ALLOW_INTS;
  return scm_cons (old_handler, SCM_MAKINUM (old_action.sa_flags));
#else
  if (query_only)
    {
      if ((old_chandler = signal (csig, SIG_IGN)) == SIG_ERR)
	SCM_SYSERROR;
      if (signal (csig, old_chandler) == SIG_ERR)
	SCM_SYSERROR;
    }
  else
    {
      if ((old_chandler = signal (csig, chandler)) == SIG_ERR)
	SCM_SYSERROR;
      if (save_handler)
	orig_handlers[csig] = old_chandler;
    }
  if (old_chandler == SIG_DFL || old_chandler == SIG_IGN)
    old_handler = scm_long2num ((long) old_chandler);
  SCM_ALLOW_INTS;
  return scm_cons (old_handler, SCM_MAKINUM (0));
#endif
}
#undef FUNC_NAME

SCM_DEFINE (scm_restore_signals, "restore-signals", 0, 0, 0,
            (void),
	    "Return all signal handlers to the values they had before any call to\n"
	    "@code{sigaction} was made.  The return value is unspecified.")
#define FUNC_NAME s_scm_restore_signals
{
  int i;
  SCM *scheme_handlers = SCM_VELTS (*signal_handlers);

  for (i = 0; i < NSIG; i++)
    {
#ifdef HAVE_SIGACTION
      if (orig_handlers[i].sa_handler != SIG_ERR)
	{
	  if (sigaction (i, &orig_handlers[i], NULL) == -1)
	    SCM_SYSERROR;
	  orig_handlers[i].sa_handler = SIG_ERR;
	  scheme_handlers[i] = SCM_BOOL_F;
	}
#else
      if (orig_handlers[i] != SIG_ERR)
	{
	  if (signal (i, orig_handlers[i]) == SIG_ERR)
	    SCM_SYSERROR;
	  orig_handlers[i] = SIG_ERR;
	  scheme_handlers[i] = SCM_BOOL_F;
	}
#endif
    }
  return SCM_UNSPECIFIED;
}
#undef FUNC_NAME

SCM_DEFINE (scm_alarm, "alarm", 1, 0, 0,
           (SCM i),
	    "Set a timer to raise a @code{SIGALRM} signal after the specified\n"
	    "number of seconds (an integer).  It's advisable to install a signal\n"
	    "handler for\n"
	    "@code{SIGALRM} beforehand, since the default action is to terminate\n"
	    "the process.\n\n"
	    "The return value indicates the time remaining for the previous alarm,\n"
	    "if any.  The new value replaces the previous alarm.  If there was\n"
	    "no previous alarm, the return value is zero.")
#define FUNC_NAME s_scm_alarm
{
  unsigned int j;
  SCM_VALIDATE_INUM (1,i);
  j = alarm (SCM_INUM (i));
  return SCM_MAKINUM (j);
}
#undef FUNC_NAME

#ifdef HAVE_PAUSE
SCM_DEFINE (scm_pause, "pause", 0, 0, 0,
           (),
	    "Pause the current process (thread?) until a signal arrives whose\n"
	    "action is to either terminate the current process or invoke a\n"
	    "handler procedure.  The return value is unspecified.")
#define FUNC_NAME s_scm_pause
{
  pause ();
  return SCM_UNSPECIFIED;
}
#undef FUNC_NAME
#endif

SCM_DEFINE (scm_sleep, "sleep", 1, 0, 0,
           (SCM i),
	    "Wait for the given number of seconds (an integer) or until a signal\n"
	    "arrives.  The return value is zero if the time elapses or the number\n"
	    "of seconds remaining otherwise.")
#define FUNC_NAME s_scm_sleep
{
  unsigned long j;
  SCM_VALIDATE_INUM_MIN (1,i,0);
#ifdef USE_THREADS
  j = scm_thread_sleep (SCM_INUM(i));
#else
  j = sleep (SCM_INUM(i));
#endif
  return scm_ulong2num (j);
}
#undef FUNC_NAME

#if defined(USE_THREADS) || defined(HAVE_USLEEP)
SCM_DEFINE (scm_usleep, "usleep", 1, 0, 0,
           (SCM i),
	    "Sleep for I microseconds.  @code{usleep} is not available on\n"
	    "all platforms.")
#define FUNC_NAME s_scm_usleep
{
  SCM_VALIDATE_INUM_MIN (1,i,0);

#ifdef USE_THREADS
  /* If we have threads, we use the thread system's sleep function.  */
  {
    unsigned long j = scm_thread_usleep (SCM_INUM (i));
    return scm_ulong2num (j);
  }
#else
#ifdef USLEEP_RETURNS_VOID
  usleep (SCM_INUM (i));
  return SCM_INUM0;
#else
  {
    int j = usleep (SCM_INUM (i));
    return SCM_MAKINUM (j);
  }
#endif
#endif
}
#undef FUNC_NAME
#endif /* GUILE_ISELECT || HAVE_USLEEP */

SCM_DEFINE (scm_raise, "raise", 1, 0, 0,
           (SCM sig),
	    "\n"
	    "Sends a specified signal @var{sig} to the current process, where\n"
	    "@var{sig} is as described for the kill procedure.")
#define FUNC_NAME s_scm_raise
{
  SCM_VALIDATE_INUM (1,sig);
  SCM_DEFER_INTS;
  if (kill (getpid (), (int) SCM_INUM (sig)) != 0)
    SCM_SYSERROR;
  SCM_ALLOW_INTS;
  return SCM_UNSPECIFIED;
}
#undef FUNC_NAME



void
scm_init_scmsigs ()
{
  SCM thunk;
  int i;

  signal_handlers =
    SCM_CDRLOC (scm_sysintern ("signal-handlers",
			       scm_c_make_vector (NSIG, SCM_BOOL_F)));
  thunk = scm_make_gsubr ("%deliver-signals", 0, 0, 0,
			  sys_deliver_signals);
  signal_async = scm_system_async (thunk);

  for (i = 0; i < NSIG; i++)
    {
      got_signal[i] = 0;
#ifdef HAVE_SIGACTION
      orig_handlers[i].sa_handler = SIG_ERR;

#else
      orig_handlers[i] = SIG_ERR;
#endif

#ifdef HAVE_RESTARTABLE_SYSCALLS
      /* If HAVE_RESTARTABLE_SYSCALLS is defined, it's important that
	 signals really are restartable.  don't rely on the same
	 run-time that configure got: reset the default for every signal.
      */
#ifdef HAVE_SIGINTERRUPT
      siginterrupt (i, 0);
#elif defined(SA_RESTART)
      {
	struct sigaction action;

	sigaction (i, NULL, &action);
	if (!(action.sa_flags & SA_RESTART))
	  {
	    action.sa_flags |= SA_RESTART;
	    sigaction (i, &action, NULL);
	  }
      }
#endif
      /* if neither siginterrupt nor SA_RESTART are available we may
	 as well assume that signals are always restartable.  */
#endif
    }

  scm_sysintern ("NSIG", scm_long2num (NSIG));
  scm_sysintern ("SIG_IGN", scm_long2num ((long) SIG_IGN));
  scm_sysintern ("SIG_DFL", scm_long2num ((long) SIG_DFL));
#ifdef SA_NOCLDSTOP
  scm_sysintern ("SA_NOCLDSTOP", scm_long2num (SA_NOCLDSTOP));
#endif
#ifdef SA_RESTART
  scm_sysintern ("SA_RESTART", scm_long2num (SA_RESTART));
#endif

#ifndef SCM_MAGIC_SNARFER
#include "libguile/scmsigs.x"
#endif
}


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