/****************************************************************************
 * sched/work_thread.c
 *
 *   Copyright (C) 2009-2011 Gregory Nutt. All rights reserved.
 *   Author: Gregory Nutt <spudmonkey@racsa.co.cr>
 *
 * 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 <stdint.h>
#include <unistd.h>
#include <queue.h>
#include <assert.h>
#include <errno.h>
#include <debug.h>

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

#include "os_internal.h"
#include "work_internal.h"

#ifdef CONFIG_SCHED_WORKQUEUE

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

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

/****************************************************************************
 * Public Variables
 ****************************************************************************/

/* The queue of pending work */

struct dq_queue_s g_work;

/* The task ID of the worker thread */

#ifdef CONFIG_SCHED_WORKQUEUE
pid_t g_worker;
#endif

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

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

/****************************************************************************
 * Public Functions
 ****************************************************************************/
/****************************************************************************
 * Name: work_thread
 *
 * Description:
 *   This is the main worker thread that performs actions placed on the work
 *   list.  It also performs periodic garbage collection (that is performed
 *   by the idle thread if CONFIG_SCHED_WORKQUEUE is not defined).
 *
 * Input parameters:
 *   argc, argv (not used)
 *
 * Returned Value:
 *   Does not return
 *
 ****************************************************************************/

int work_thread(int argc, char *argv[])
{
  volatile FAR struct work_s *work;
  worker_t  worker;
  FAR void *arg;
  uint32_t elapsed;
  uint32_t remaining;
  uint32_t next;
  int usec;
  irqstate_t flags;

  /* Loop forever */

  usec = CONFIG_SCHED_WORKPERIOD;
  flags = irqsave();
  for (;;)
    {
      /* Wait awhile to check the work list.  We will wait here until either
       * the time elapses or until we are awakened by a signal.
       */

      usleep(usec);
      irqrestore(flags);

      /* First, perform garbage collection.  This cleans-up memory de-allocations
       * that were queued because they could not be freed in that execution
       * context (for example, if the memory was freed from an interrupt handler).
       * NOTE: If the work thread is disabled, this clean-up is performed by
       * the IDLE thread (at a very, very lower priority).
       */

      sched_garbagecollection();

      /* Then process queued work.  We need to keep interrupts disabled while
       * we process items in the work list.
       */

      next  = CONFIG_SCHED_WORKPERIOD / USEC_PER_TICK;
      flags = irqsave();
      work  = (FAR struct work_s *)g_work.head;
      while (work)
        {
          /* Is this work ready?  It is ready if there is no delay or if
           * the delay has elapsed. qtime is the time that the work was added
           * to the work queue.  It will always be greater than or equal to
           * zero.  Therefore a delay of zero will always execute immediately.
           */

          elapsed = clock_systimer() - work->qtime;
          if (elapsed >= work->delay)
            {
              /* Remove the ready-to-execute work from the list */

              (void)dq_rem((struct dq_entry_s *)work, &g_work);

              /* Extract the work description from the entry (in case the work
               * instance by the re-used after it has been de-queued).
               */

              worker = work->worker;
              arg    = work->arg;

              /* Mark the work as no longer being queued */

              work->worker = NULL;

              /* Do the work.  Re-enable interrupts while the work is being
               * performed... we don't have any idea how long that will take!
               */

              irqrestore(flags);
              worker(arg);

              /* Now, unfortunately, since we re-enabled interrupts we don't
               * know the state of the work list and we will have to start
               * back at the head of the list.
               */

              flags = irqsave();
              work  = (FAR struct work_s *)g_work.head;
            }
          else
            {
              /* This one is not ready.. will it be ready before the next
               * scheduled wakeup interval?
               */

              remaining = elapsed - work->delay;
              if (remaining < next)
                {
                  /* Yes.. Then schedule to wake up when the work is ready */

                  next = remaining;
                }
              
              /* Then try the next in the list. */

              work = (FAR struct work_s *)work->dq.flink;
            }
        }

      /* Now calculate the microsecond delay we should wait */

      usec = next * USEC_PER_TICK;
    }

  return OK; /* To keep some compilers happy */
}
#endif /* CONFIG_SCHED_WORKQUEUE */
