/*****************************************************************************
 * sched/task_childstatus.c
 *
 *   Copyright (C) 2013 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 <sched.h>
#include <errno.h>
#include <debug.h>

#include "os_internal.h"

#if defined(CONFIG_SCHED_HAVE_PARENT) && defined(CONFIG_SCHED_CHILD_STATUS)

/*****************************************************************************
 * Pre-processor Definitions
 *****************************************************************************/
/* Note that there cannot be more that CONFIG_MAX_TASKS tasks in total.
 * However, the number of child status structures may need to be significantly
 * larger because this number includes the maximum number of tasks that are
 * running PLUS the number of tasks that have exit'ed without having their
 * exit status reaped (via wait(), waitid(), or waitpid()).
 *
 * Obviously, if tasks spawn children indefinitely and never have the exit
 * status reaped, then you have a memory leak!
 */

#if !defined(CONFIG_PREALLOC_CHILDSTATUS) || CONFIG_PREALLOC_CHILDSTATUS == 0
#  undef  CONFIG_PREALLOC_CHILDSTATUS
#  define CONFIG_PREALLOC_CHILDSTATUS (2*CONFIG_MAX_TASKS)
#endif

#ifndef CONFIG_DEBUG
#  undef CONFIG_DEBUG_CHILDSTATUS
#endif

/*****************************************************************************
 * Private Types
 *****************************************************************************/
/* Globals are maintained in a structure to minimize name collisions. */

struct child_pool_s
{
  struct child_status_s alloc[CONFIG_PREALLOC_CHILDSTATUS];
  FAR struct child_status_s *freelist;
};

/*****************************************************************************
 * Private Data
 *****************************************************************************/

static struct child_pool_s g_child_pool;

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

/*****************************************************************************
 * Name: task_dumpchildren
 *
 * Description:
 *   Dump all of the children when the part TCB list is modified.
 *
 * Parameters:
 *   tcb - The parent TCB.
 *
 * Return Value:
 *   None.
 *
 * Assumptions:
 *   Called early in initialization.  No special precautions are required.
 *
 *****************************************************************************/

#ifdef CONFIG_DEBUG_CHILDSTATUS
static void task_dumpchildren(FAR _TCB *tcb, FAR const char *msg)
{
  FAR struct child_status_s *child;
  int i;

  dbg("Parent TCB=%p: %s\n", tcb, msg);
  for (i = 0, child = tcb->children; child; i++, child = child->flink)
    {
      dbg("  %d. ch_flags=%02x ch_pid=%d ch_status=%d\n",
          i, child->ch_flags, child->ch_pid, child->ch_status);
    }
}
#else
#  task_dumpchildren(t,m)
#endif

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

/*****************************************************************************
 * Name: task_initialize
 *
 * Description:
 *   Initialize task related status.  At present, this includes only the
 *   initialize of the child status pool.
 *
 * Parameters:
 *   None.
 *
 * Return Value:
 *   None.
 *
 * Assumptions:
 *   Called early in initialization.  No special precautions are required.
 *
 *****************************************************************************/

void task_initialize(void)
{
  FAR struct child_status_s *curr;
  FAR struct child_status_s *prev;
  int i;

  /* Save all of the child status structures in a free list */

  prev = &g_child_pool.alloc[0];
  g_child_pool.freelist = prev;
  for (i = 0; i < CONFIG_PREALLOC_CHILDSTATUS; i++)
    {
      curr        = &g_child_pool.alloc[i];
      prev->flink = curr;
      prev        = curr;
    }
}

/*****************************************************************************
 * Name: task_allocchild
 *
 * Description:
 *   Allocate a child status structure by removing the next entry from a
 *   free list.
 *
 * Parameters:
 *   None.
 *
 * Return Value:
 *   On success, a non-NULL pointer to a child status structure.  NULL is
 *   returned if there are no remaining, pre-allocated child status structures.
 *
 * Assumptions:
 *   Called during task creation in a safe context.  No special precautions
 *   are required here.
 *
 *****************************************************************************/

FAR struct child_status_s *task_allocchild(void)
{
  FAR struct child_status_s *ret;

  /* Return the status block at the head of the free list */

  ret = g_child_pool.freelist;
  if (ret)
    {
      g_child_pool.freelist = ret->flink;
      ret->flink            = NULL;
    }

  return ret;
}

/*****************************************************************************
 * Name: task_freechild
 *
 * Description:
 *   Release a child status structure by returning it to a free list.
 *
 * Parameters:
 *   status - The child status structure to be freed.
 *
 * Return Value:
 *   None.
 *
 * Assumptions:
 *   Called during task creation in a safe context.  No special precautions
 *   are required here.
 *
 *****************************************************************************/

void task_freechild(FAR struct child_status_s *child)
{
  /* Return the child status structure to the free list  */

  if (child)
    {
      child->flink          = g_child_pool.freelist;
      g_child_pool.freelist = child;
    }
}

/*****************************************************************************
 * Name: task_addchild
 *
 * Description:
 *   Add a child status structure in the given TCB.
 *
 * Parameters:
 *   tcb    - The TCB of the parent task to containing the child status.
 *   child  - The structure to be added
 *
 * Return Value:
 *   N
 *
 * Assumptions:
 *   Called during task creation processing in a safe context.  No special
 *   precautions are required here.
 *
 *****************************************************************************/

void task_addchild(FAR _TCB *tcb, FAR struct child_status_s *child)
{
  /* Add the entry into the TCB list of children */

  child->flink  = tcb->children;
  tcb->children = child;

  task_dumpchildren(tcb, "task_addchild");
}

/*****************************************************************************
 * Name: task_findchild
 *
 * Description:
 *   Find a child status structure in the given TCB.  A reference to the
 *   child structure is returned, but the child remains the the TCB's list
 *   of children.
 *
 * Parameters:
 *   tcb - The TCB of the parent task to containing the child status.
 *   pid - The ID of the child to find.
 *
 * Return Value:
 *   On success, a non-NULL pointer to a child status structure.  NULL is
 *   returned if there is child status structure for that pid in the TCB.
 *
 * Assumptions:
 *   Called during SIGCHLD processing in a safe context.  No special precautions
 *   are required here.
 *
 *****************************************************************************/

FAR struct child_status_s *task_findchild(FAR _TCB *tcb, pid_t pid)
{
  FAR struct child_status_s *child;

  /* Find the status structure with the matching PID  */

  for (child = tcb->children; child; child = child->flink)
    {
      if (child->ch_pid == pid)
        {
          return child;
        }
    }

  return NULL;
}

/*****************************************************************************
 * Name: task_removechild
 *
 * Description:
 *   Remove one child structure from the TCB.  The child is removed, but is
 *   not yet freed.  task_freechild must be called in order to free the child
 *   status structure.
 *
 * Parameters:
 *   tcb - The TCB of the parent task to containing the child status.
 *   pid - The ID of the child to find.
 *
 * Return Value:
 *   On success, a non-NULL pointer to a child status structure.  NULL is
 *   returned if there is child status structure for that pid in the TCB.
 *
 * Assumptions:
 *   Called during SIGCHLD processing in a safe context.  No special precautions
 *   are required here.
 *
 *****************************************************************************/

FAR struct child_status_s *task_removechild(FAR _TCB *tcb, pid_t pid)
{
  FAR struct child_status_s *curr;
  FAR struct child_status_s *prev;

  /* Find the status structure with the matching PID  */

  for (prev = NULL, curr = tcb->children;
       curr;
       prev = curr, curr = curr->flink)
    {
      if (curr->ch_pid == pid)
        {
          break;
        }
    }

  /* Did we find it?  If so, remove it from the TCB. */

  if (curr)
    {
      /* Do we remove it from mid-list?  Or from the head of the list? */

      if (prev)
        {
          prev->flink = curr->flink;
        }
      else
        {
          tcb->children = curr->flink;
        }

      curr->flink = NULL;
      task_dumpchildren(tcb, "task_removechild");
    }
 
  return curr;
}

/*****************************************************************************
 * Name: task_removechildren
 *
 * Description:
 *   Remove and free all child structure from the TCB.
 *
 * Parameters:
 *   tcb - The TCB of the parent task to containing the child status.
 *
 * Return Value:
 *   None.
 *
 * Assumptions:
 *   Called during task exit processing in a safe context.  No special
 *   precautions are required here.
 *
 *****************************************************************************/

void task_removechildren(FAR _TCB *tcb)
{
  FAR struct child_status_s *curr;
  FAR struct child_status_s *next;

  /* Remove all child structures for the TCB and return them to the freelist  */

  for (curr = tcb->children; curr; curr = next)
    {
      next = curr->flink;
      task_freechild(curr);
    }

  tcb->children = NULL;
  task_dumpchildren(tcb, "task_removechildren");
}

#endif /* CONFIG_SCHED_HAVE_PARENT && CONFIG_SCHED_CHILD_STATUS */