nuttx/sched/sched/sched_mergepending.c

/****************************************************************************
 * sched/sched/sched_mergepending.c
 *
 *   Copyright (C) 2007, 2009, 2012, 2016 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 <stdbool.h>
#include <sched.h>
#include <queue.h>
#include <assert.h>

#include "sched/sched.h"

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

/****************************************************************************
 * Name: sched_mergepending
 *
 * Description:
 *   This function merges the prioritized g_pendingtasks list into the
 *   prioritized ready-to-run task list.
 *
 * Inputs:
 *   None
 *
 * Return Value:
 *   true if the head of the ready-to-run task list has changed indicating
 *     a context switch is needed.
 *
 * Assumptions:
 * - The caller has established a critical section before
 *   calling this function (calling sched_lock() first is NOT
 *   a good idea -- use irqsave()).
 * - The caller handles the condition that occurs if the
 *   the head of the sched_mergTSTATE_TASK_PENDINGs is changed.
 *
 ****************************************************************************/

#ifndef CONFIG_SMP
bool sched_mergepending(void)
{
  FAR struct tcb_s *ptcb;
  FAR struct tcb_s *pnext;
  FAR struct tcb_s *rtcb;
  FAR struct tcb_s *rprev;
  bool ret = false;

  /* Initialize the inner search loop */

  rtcb = this_task();

  /* Process every TCB in the g_pendingtasks list */

  for (ptcb = (FAR struct tcb_s *)g_pendingtasks.head;
       ptcb;
       ptcb = pnext)
    {
      pnext = ptcb->flink;

      /* REVISIT:  Why don't we just remove the ptcb from pending task list
       * and call sched_addreadytorun?
       */

      /* Search the ready-to-run list to find the location to insert the
       * new ptcb. Each is list is maintained in ascending sched_priority
       * order.
       */

      for (;
           (rtcb && ptcb->sched_priority <= rtcb->sched_priority);
           rtcb = rtcb->flink);

      /* Add the ptcb to the spot found in the list.  Check if the
       * ptcb goes at the ends of the ready-to-run list. This would be
       * error condition since the idle test must always be at the end of
       * the ready-to-run list!
       */

      ASSERT(rtcb);

      /* The ptcb goes just before rtcb */

      rprev = rtcb->blink;
      if (!rprev)
        {
          /* Special case: Inserting ptcb at the head of the list */
          /* Inform the instrumentation layer that we are switching tasks */

          sched_note_switch(rtcb, ptcb);

          /* Then insert at the head of the list */

          ptcb->flink       = rtcb;
          ptcb->blink       = NULL;
          rtcb->blink       = ptcb;
          g_readytorun.head = (FAR dq_entry_t *)ptcb;
          rtcb->task_state  = TSTATE_TASK_READYTORUN;
          ptcb->task_state  = TSTATE_TASK_RUNNING;
          ret               = true;
        }
      else
        {
          /* Insert in the middle of the list */

          ptcb->flink       = rtcb;
          ptcb->blink       = rprev;
          rprev->flink      = ptcb;
          rtcb->blink       = ptcb;
          ptcb->task_state  = TSTATE_TASK_READYTORUN;
        }

      /* Set up for the next time through */

      rtcb = ptcb;
    }

  /* Mark the input list empty */

  g_pendingtasks.head = NULL;
  g_pendingtasks.tail = NULL;

  return ret;
}
#endif /* !CONFIG_SMP */

/****************************************************************************
 * Name: sched_mergepending
 *
 * Description:
 *   This function merges the prioritized g_pendingtasks list into the
 *   prioritized ready-to-run task list.
 *
 * Inputs:
 *   None
 *
 * Return Value:
 *   true if the head of the ready-to-run task list has changed indicating
 *     a context switch is needed.
 *
 * Assumptions:
 * - The caller has established a critical section before
 *   calling this function (calling sched_lock() first is NOT
 *   a good idea -- use irqsave()).
 * - The caller handles the condition that occurs if the
 *   the head of the sched_mergTSTATE_TASK_PENDINGs is changed.
 *
 ****************************************************************************/

#ifdef CONFIG_SMP
bool sched_mergepending(void)
{
  FAR struct tcb_s *ptcb;
  bool ret = false;

  /* Remove and process every TCB in the g_pendingtasks list */

  for (ptcb = (FAR struct tcb_s *)dq_remfirst((FAR dq_queue_t *)&g_pendingtasks);
       ptcb != NULL;
       ptcb = (FAR struct tcb_s *)dq_remfirst((FAR dq_queue_t *)&g_pendingtasks))
    {
      /* Add the pending task to the correct ready-to-run list */

      ret |= sched_addreadytorun(ptcb);
    }

  return ret;
}
#endif /* CONFIG_SMP */