px4-firmware/nuttx/sched/sleep.c

/****************************************************************************
 * sched/sleep.c
 *
 *   Copyright (C) 2007, 2009, 2012 Gregory Nutt. All rights reserved.
 *   Author: Gregory Nutt <gnutt@nuttx.org>
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 *
 * 1. Redistributions of source code must retain the above copyright
 *    notice, this list of conditions and the following disclaimer.
 * 2. Redistributions in binary form must reproduce the above copyright
 *    notice, this list of conditions and the following disclaimer in
 *    the documentation and/or other materials provided with the
 *    distribution.
 * 3. Neither the name NuttX nor the names of its contributors may be
 *    used to endorse or promote products derived from this software
 *    without specific prior written permission.
 *
 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
 * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
 * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS
 * FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE
 * COPYRIGHT OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT,
 * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING,
 * BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS
 * OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED
 * AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN
 * ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
 * POSSIBILITY OF SUCH DAMAGE.
 *
 ****************************************************************************/

/****************************************************************************
 * Included Files
 ****************************************************************************/

#include <nuttx/config.h>

#include <unistd.h>
#include <signal.h>

#include <nuttx/clock.h>
#include <arch/irq.h>

/****************************************************************************
 * Preprocessor Definitions
 ****************************************************************************/

/****************************************************************************
 * Private Type Definitions
 ****************************************************************************/

/****************************************************************************
 * Global Variables
 ****************************************************************************/

/****************************************************************************
 * Private Variables
 ****************************************************************************/

/****************************************************************************
 * Private Function Prototypes
 ****************************************************************************/

/****************************************************************************
 * Public Functions
 ****************************************************************************/

/****************************************************************************
 * Name: sleep
 *
 * Description:
 *   The sleep() function will cause the calling thread to be suspended from
 *   execution until either the number of real-time seconds specified by the
 *   argument 'seconds' has elapsed or a signal is delivered to the calling
 *   thread and its action is to invoke a signal-catching function or to
 *   terminate the process. The suspension time may be longer than requested
 *   due to the scheduling of other activity by the system.
 *
 *   If a SIGALRM signal is generated for the calling process during
 *   execution of sleep() and if the SIGALRM signal is being ignored or
 *   blocked from delivery, it is unspecified whether sleep() returns
 *   when the SIGALRM signal is scheduled. If the signal is being blocked, it
 *   is also unspecified whether it remains pending after sleep() returns or
 *   it is discarded.
 *
 *   If a SIGALRM signal is generated for the calling process during
 *   execution of sleep(), except as a result of a prior call to alarm(),
 *   and if the SIGALRM signal is not being ignored or blocked from delivery,
 *   it is unspecified whether that signal has any effect other than causing
 *   sleep() to return.
 *
 *   If a signal-catching function interrupts sleep() and examines or changes
 *   either the time a SIGALRM is scheduled to be generated, the action
 *   associated with the SIGALRM signal, or whether the SIGALRM signal is
 *   blocked from delivery, the results are unspecified.
 *
 *   If a signal-catching function interrupts sleep() and calls siglongjmp()
 *   or longjmp() to restore an environment saved prior to the sleep() call,
 *   the action associated with the SIGALRM signal and the time at which a
 *   SIGALRM signal is scheduled to be generated are unspecified. It is also
 *   unspecified whether the SIGALRM signal is blocked, unless the process'
 *   signal mask is restored as part of the environment.
 *
 *   Implementations may place limitations on the granularity of timer values.
 *   For each interval timer, if the requested timer value requires a finer
 *   granularity than the implementation supports, the actual timer value will
 *   be rounded up to the next supported value. 
 *
 *   Interactions between sleep() and any of setitimer(), ualarm() or sleep()
 *   are unspecified. 
 *
 * Parameters:
 *   seconds
 *
 * Returned Value:
 *   If sleep() returns because the requested time has elapsed, the value
 *   returned will be 0. If sleep() returns because of premature arousal due
 *   to delivery of a signal, the return value will be the "unslept" amount
 *   (the requested time minus the time actually slept) in seconds.
 *
 * Assumptions:
 *
 ****************************************************************************/

unsigned int sleep(unsigned int seconds)
{
  sigset_t set;
  struct timespec ts;
  struct siginfo value;
  irqstate_t flags;
  uint32_t start;
  int32_t elapsed;
  int32_t remaining = 0;

  /* Don't sleep if seconds == 0 */

  if (seconds)
    {
      /* Set up for the sleep.  Using the empty set means that we are not
       * waiting for any particualar signal.  However, any unmasked signal
       * can still awaken sigtimedwait().
       */

      (void)sigemptyset(&set);
      ts.tv_sec  = seconds;
      ts.tv_nsec = 0;

      /* Interrupts are disabled around the following so that it is atomic */
       
      flags = irqsave();
 
      /* Get the current time then sleep for the requested time.  
       * sigtimedwait() cannot succeed.  It should always return error with
       * either (1) EAGAIN meaning that the timeout occurred, or (2) EINTR
       * meaning that some other unblocked signal was caught.
       */

      start = clock_systimer();
      (void)sigtimedwait(&set, &value, &ts);

      /* Calculate the elapsed time (in clock ticks) when we wake up from the sleep.
       * This is really only necessary if we were awakened from the sleep early
       * due to the receipt of a signal.
       */

      elapsed = clock_systimer() - start;
      irqrestore(flags);

      /* Get the remaining, un-waited seconds. Note that this calculation
       * truncates the elapsed seconds in the division.  We may have slept some
       * fraction of a second longer than this!  But if the calculation is less
       * than the 'seconds', we certainly did not sleep for the complete
       * requested interval.
       */

      remaining = (int32_t)seconds - elapsed / TICK_PER_SEC;

      /* Make sure that the elapsed time is non-negative (this should always
       * be the case unless something exceptional happened while were we
       * sleeping -- like the clock was reset or we went into a low power mode,
       * OR if we had to wait a long time to run again after calling
       * sigtimedwait() making 'elapsed' bigger than it should have been).
       */

      if (remaining < 0)
        {
          remaining = 0;
        }
    }

  return (unsigned int)remaining;
}