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setitimer.c

/* Copyright (C) 1994,1995,1996,1997,2000,2001 Free Software Foundation, Inc.
   This file is part of the GNU C Library.

   The GNU C 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.

   The GNU C 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 the GNU C Library; if not, write to the Free
   Software Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA
   02111-1307 USA.  */

#include <stddef.h>
#include <errno.h>
#include <sys/time.h>
#include <time.h>
#include <hurd.h>
#include <hurd/signal.h>
#include <hurd/sigpreempt.h>
#include <hurd/msg_request.h>
#include <mach/message.h>

/* XXX Temporary cheezoid implementation of ITIMER_REAL/SIGALRM.  */

spin_lock_t _hurd_itimer_lock = SPIN_LOCK_INITIALIZER;
struct itimerval _hurd_itimerval; /* Current state of the timer.  */
mach_port_t _hurd_itimer_port;      /* Port the timer thread blocks on.  */
thread_t _hurd_itimer_thread; /* Thread waiting for timeout.  */
int _hurd_itimer_thread_suspended; /* Nonzero if that thread is suspended.  */
vm_address_t _hurd_itimer_thread_stack_base; /* Base of its stack.  */
vm_address_t _hurd_itimer_thread_stack_size; /* Size of its stack.  */
struct timeval _hurd_itimer_started; /* Time the thread started waiting.  */

static void
quantize_timeval (struct timeval *tv)
{
  static time_t quantum = -1;
  
  if (quantum == -1)
    quantum = 1000000 / __getclktck ();

  tv->tv_usec = ((tv->tv_usec + (quantum - 1)) / quantum) * quantum;
  if (tv->tv_usec >= 1000000)
    {
      ++tv->tv_sec;
      tv->tv_usec -= 1000000;
    }
}

static inline void
subtract_timeval (struct timeval *from, const struct timeval *subtract)
{
  from->tv_usec -= subtract->tv_usec;
  from->tv_sec -= subtract->tv_sec;
  while (from->tv_usec < 0)
    {
      --from->tv_sec;
      from->tv_usec += 1000000;
    }
}

/* Function run by the itimer thread.
   This code must be very careful not ever to require a MiG reply port.  */

static void
timer_thread (void)
{
  while (1)
    {
      error_t err;
      /* The only message we ever expect to receive is the reply from the
         signal thread to a sig_post call we did.  We never examine the
       contents.  */
      struct
      {
        mach_msg_header_t header;
        error_t return_code;
      } msg;

      /* Wait for a message on a port that noone sends to.  The purpose is
       the receive timeout.  Notice interrupts so that if we are
       thread_abort'd, we will loop around and fetch new values from
       _hurd_itimerval.  */
      err = __mach_msg (&msg.header,
                  MACH_RCV_MSG|MACH_RCV_TIMEOUT|MACH_RCV_INTERRUPT,
                  0, 0, _hurd_itimer_port,
                  _hurd_itimerval.it_value.tv_sec * 1000 +
                  _hurd_itimerval.it_value.tv_usec / 1000,
                  MACH_PORT_NULL);
      switch (err)
      {
      case MACH_RCV_TIMED_OUT:
        /* We got the expected timeout.  Send a message to the signal
           thread to tell it to post a SIGALRM signal.  We use
           _hurd_itimer_port as the reply port just so we will block until
           the signal thread has frobnicated things to reload the itimer or
           has terminated this thread.  */
        __msg_sig_post_request (_hurd_msgport,
                          _hurd_itimer_port,
                          MACH_MSG_TYPE_MAKE_SEND_ONCE,
                          SIGALRM, 0, __mach_task_self ());
        break;

      case MACH_RCV_INTERRUPTED:
        /* We were thread_abort'd.  This is to tell us that
           _hurd_itimerval has changed and we need to reexamine it
           and start waiting with the new timeout value.  */
        break;

      case MACH_MSG_SUCCESS:
        /* We got the reply message from the sig_post_request above.
           Ignore it and reexamine the timer value.  */
        __mach_msg_destroy (&msg.header); /* Just in case.  */
        break;

      default:
        /* Unexpected lossage.  Oh well, keep trying.  */
        break;
      }
    }
}


static sighandler_t
restart_itimer (struct hurd_signal_preemptor *preemptor,
            struct hurd_sigstate *ss,
            int *signo, struct hurd_signal_detail *detail)
{
  static int setitimer_locked (const struct itimerval *new,
                         struct itimerval *old, void *crit);

  /* This function gets called in the signal thread
     each time a SIGALRM is arriving (even if blocked).  */
  struct itimerval it;

  /* Either reload or disable the itimer.  */
  __spin_lock (&_hurd_itimer_lock);
  it.it_value = it.it_interval = _hurd_itimerval.it_interval;
  setitimer_locked (&it, NULL, NULL);

  /* Continue with normal delivery (or hold, etc.) of SIGALRM.  */
  return SIG_ERR;
}


/* Called before any normal SIGALRM signal is delivered.
   Reload the itimer, or disable the itimer.  */

static int
setitimer_locked (const struct itimerval *new, struct itimerval *old,
              void *crit)
{
  struct itimerval newval;
  struct timeval now, remaining, elapsed;
  struct timeval old_interval;
  error_t err;

  inline void kill_itimer_thread (void)
    {
      __thread_terminate (_hurd_itimer_thread);
      __vm_deallocate (__mach_task_self (),
                   _hurd_itimer_thread_stack_base,
                   _hurd_itimer_thread_stack_size);
      _hurd_itimer_thread = MACH_PORT_NULL;
    }

  if (!new)
    {
      /* Just return the current value in OLD without changing anything.
       This is what BSD does, even though it's not documented. */
      if (old)
      *old = _hurd_itimerval;
      spin_unlock (&_hurd_itimer_lock);
      _hurd_critical_section_unlock (crit);
      return 0;
    }

  newval = *new;
  quantize_timeval (&newval.it_interval);
  quantize_timeval (&newval.it_value);
  if ((newval.it_value.tv_sec | newval.it_value.tv_usec) != 0)
    {
      /* Make sure the itimer thread is set up.  */

      /* Set up a signal preemptor global for all threads to
       run `restart_itimer' each time a SIGALRM would arrive.  */
      static struct hurd_signal_preemptor preemptor =
      {
        __sigmask (SIGALRM), 0, 0,
        &restart_itimer,
      };
      __mutex_lock (&_hurd_siglock);
      if (! preemptor.next && _hurdsig_preemptors != &preemptor)
      {
        preemptor.next = _hurdsig_preemptors;
        _hurdsig_preemptors = &preemptor;
      }
      __mutex_unlock (&_hurd_siglock);

      if (_hurd_itimer_port == MACH_PORT_NULL)
      {
        /* Allocate a receive right that the itimer thread will
           block waiting for a message on.  */
        if (err = __mach_port_allocate (__mach_task_self (),
                                MACH_PORT_RIGHT_RECEIVE,
                                &_hurd_itimer_port))
          goto out;
      }

      if (_hurd_itimer_thread == MACH_PORT_NULL)
      {
        /* Start up the itimer thread running `timer_thread' (below).  */
        if (err = __thread_create (__mach_task_self (),
                             &_hurd_itimer_thread))
          return __hurd_fail (err);
        _hurd_itimer_thread_stack_base = 0; /* Anywhere.  */
        _hurd_itimer_thread_stack_size = __vm_page_size; /* Small stack.  */
        if (err = __mach_setup_thread (__mach_task_self (),
                               _hurd_itimer_thread,
                               &timer_thread,
                               &_hurd_itimer_thread_stack_base,
                               &_hurd_itimer_thread_stack_size))
          {
            __thread_terminate (_hurd_itimer_thread);
            _hurd_itimer_thread = MACH_PORT_NULL;
            goto out;
          }
        _hurd_itimer_thread_suspended = 1;
      }
    }

  if ((newval.it_value.tv_sec | newval.it_value.tv_usec) != 0 || old != NULL)
    {
      /* Calculate how much time is remaining for the pending alarm.  */
      if (__gettimeofday (&now, NULL) < 0)
      {
        __spin_unlock (&_hurd_itimer_lock);
        _hurd_critical_section_unlock (crit);
        return -1;
      }
      elapsed = now;
      subtract_timeval (&elapsed, &_hurd_itimer_started);
      remaining = _hurd_itimerval.it_value;
      if (timercmp (&remaining, &elapsed, <))
      {
        /* Hmm.  The timer should have just gone off, but has not been reset.
           This is a possible timing glitch.  The alarm will signal soon. */
        /* XXX wrong */
        remaining.tv_sec = 0;
        remaining.tv_usec = 0;
      }
      else
      subtract_timeval (&remaining, &elapsed);

      /* Remember the old reload interval before changing it.  */
      old_interval = _hurd_itimerval.it_interval;

      /* Record the starting time that the timer interval relates to.  */
      _hurd_itimer_started = now;
    }

  /* Load the new itimer value.  */
  _hurd_itimerval = newval;

  if ((newval.it_value.tv_sec | newval.it_value.tv_usec) == 0)
    {
      /* Disable the itimer.  */
      if (_hurd_itimer_thread && !_hurd_itimer_thread_suspended)
      {
        /* Suspend the itimer thread so it does nothing.  Then abort its
           kernel context so that when the thread is resumed, mach_msg
           will return to timer_thread (below) and it will fetch new
           values from _hurd_itimerval.  */
        if ((err = __thread_suspend (_hurd_itimer_thread)) ||
            (err = __thread_abort (_hurd_itimer_thread)))
          /* If we can't save it for later, nuke it.  */
          kill_itimer_thread ();
        else
          _hurd_itimer_thread_suspended = 1;
      }
    }
  /* See if the timeout changed.  If so, we must alert the itimer thread.  */
  else if (remaining.tv_sec != newval.it_value.tv_sec ||
         remaining.tv_usec != newval.it_value.tv_usec)
    {
      /* The timeout value is changing.  Tell the itimer thread to
       reexamine it and start counting down.  If the itimer thread is
       marked as suspended, either we just created it, or it was
       suspended and thread_abort'd last time the itimer was disabled;
       either way it will wake up and start waiting for the new timeout
       value when we resume it.  If it is not suspended, the itimer
       thread is waiting to deliver a pending alarm that we will override
       (since it would come later than the new alarm being set);
       thread_abort will make mach_msg return MACH_RCV_INTERRUPTED, so it
       will loop around and use the new timeout value.  */
      if (err = (_hurd_itimer_thread_suspended
             ? __thread_resume : __thread_abort) (_hurd_itimer_thread))
      {
        kill_itimer_thread ();
        goto out;
      }
      _hurd_itimer_thread_suspended = 0;
    }

  __spin_unlock (&_hurd_itimer_lock);
  _hurd_critical_section_unlock (crit);

  if (old != NULL)
    {
      old->it_value = remaining;
      old->it_interval = old_interval;
    }
  return 0;

 out:
  __spin_unlock (&_hurd_itimer_lock);
  _hurd_critical_section_unlock (crit);
  return __hurd_fail (err);
}

/* Set the timer WHICH to *NEW.  If OLD is not NULL,
   set *OLD to the old value of timer WHICH.
   Returns 0 on success, -1 on errors.  */
int
__setitimer (enum __itimer_which which, const struct itimerval *new,
           struct itimerval *old)
{
  void *crit;

  switch (which)
    {
    default:
      return __hurd_fail (EINVAL);

    case ITIMER_VIRTUAL:
    case ITIMER_PROF:
      return __hurd_fail (ENOSYS);

    case ITIMER_REAL:
      break;
    }

  crit = _hurd_critical_section_lock ();
  __spin_lock (&_hurd_itimer_lock);
  return setitimer_locked (new, old, crit);
}

static void
fork_itimer (void)
{
  /* We must restart the itimer in the child.  */

  struct itimerval it;

  __spin_lock (&_hurd_itimer_lock);
  _hurd_itimer_thread = MACH_PORT_NULL;
  it = _hurd_itimerval;
  it.it_value = it.it_interval;

  setitimer_locked (&it, NULL, NULL);

  (void) &fork_itimer;        /* Avoid gcc optimizing out the function.  */
}
text_set_element (_hurd_fork_child_hook, fork_itimer);

weak_alias (__setitimer, setitimer)

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