incubator-nuttx/sched/sched_unlock.c

/************************************************************************
 * sched/sched_unlock.c
 *
 *   Copyright (C) 2007, 2009, 2014 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
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 * 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 <nuttx/clock.h>
#include <nuttx/arch.h>

#include "os_internal.h"

/************************************************************************
 * Pre-processor Definitions
 ************************************************************************/

/************************************************************************
 * Private Type Declarations
 ************************************************************************/

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

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

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

/************************************************************************
 * Private Functions
 ************************************************************************/

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

/************************************************************************
 * Name:  sched_unlock
 *
 * Description:
 *   This function decrements the preemption lock count.  Typically this
 *   is paired with sched_lock() and concludes a critical section of
 *   code.  Preemption will not be unlocked until sched_unlock() has
 *   been called as many times as sched_lock().  When the lockcount is
 *   decremented to zero, any tasks that were eligible to preempt the
 *   current task will execute.
 *
 ************************************************************************/

int sched_unlock(void)
{
  FAR struct tcb_s *rtcb = (FAR struct tcb_s*)g_readytorun.head;

  /* Check for some special cases:  (1) rtcb may be NULL only during
   * early boot-up phases, and (2) sched_unlock() should have no
   * effect if called from the interrupt level.
   */

  if (rtcb && !up_interrupt_context())
    {
      /* Prevent context switches throughout the following */

      irqstate_t flags = irqsave();

      /* Decrement the preemption lock counter */

      if (rtcb->lockcount)
        {
          rtcb->lockcount--;
        }

      /* Check if the lock counter has decremented to zero.  If so,
       * then pre-emption has been re-enabled.
       */

      if (rtcb->lockcount <= 0)
        {
          rtcb->lockcount = 0;

          /* Release any ready-to-run tasks that have collected in
           * g_pendingtasks.
           */

          if (g_pendingtasks.head)
            {
              up_release_pending();
            }

#if CONFIG_RR_INTERVAL > 0
          /* If (1) the task that was running supported round-robin
           * scheduling and (2) if its time slice has already expired, but
           * (3) it could not slice out because pre-emption was disabled,
           * then we need to swap the task out now and reassess the interval
           * timer for the next time slice.
           */

          if ((rtcb->flags & TCB_FLAG_ROUND_ROBIN) != 0 &&
              rtcb->timeslice == 0)
            {
              /* Yes.. that is the situation.  But one more thing.  The call
               * to up_release_pending() above may have actually replaced
               * the task at the head of the read-to-run list.  In that case,
               * we need only to reset the timeslice value back to the
               * maximum.
               */

              if (rtcb != (FAR struct tcb_s*)g_readytorun.head)
                {
                  rtcb->timeslice = MSEC2TICK(CONFIG_RR_INTERVAL);
                }
#ifdef CONFIG_SCHED_TICKLESS
              else
               {
                 sched_timer_reassess();
               }
#endif
            }
#endif
        }

      irqrestore(flags);
    }

  return OK;
}