/****************************************************************************
 * sched/task/task_delete.c
 *
 *   Copyright (C) 2007-2009, 2011-2013, 2016-2017 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 <stdlib.h>
#include <errno.h>

#include <nuttx/sched.h>

#include "sched/sched.h"
#include "task/task.h"

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

/****************************************************************************
 * Name: task_delete
 *
 * Description:
 *   This function causes a specified task to cease to exist.  Its stack and
 *   TCB will be deallocated.  This function is the companion to
 *   task_create().  This is the version of the function exposed to the
 *   user; it is simply a wrapper around the internal, nxtask_terminate
 *   function.
 *
 *   The logic in this function only deletes non-running tasks.  If the
 *   'pid' parameter refers to the currently running task, then processing
 *   is redirected to exit().  This can only happen if a task calls
 *   task_delete()in order to delete itself.
 *
 *   This function obeys the semantics of pthread cancellation:  task
 *   deletion is deferred if cancellation is disabled or if deferred
 *   cancellation is supported (with cancellation points enabled).
 *
 * Input Parameters:
 *   pid - The task ID of the task to delete.  A pid of zero
 *         signifies the calling task.
 *
 * Returned Value:
 *   OK on success; or ERROR on failure with the errno variable set
 *   appropriately.
 *
 ****************************************************************************/

int task_delete(pid_t pid)
{
  FAR struct tcb_s *dtcb;
  FAR struct tcb_s *rtcb;
  int errcode;
  int ret;

  /* Check if the task to delete is the calling task:  PID=0 means to delete
   * the calling task.  In this case, task_delete() is much like exit()
   * except that it obeys the cancellation semantics.
   */

  rtcb = this_task();
  if (pid == 0)
    {
      pid = rtcb->pid;
    }

  /* Get the TCB of the task to be deleted */

  dtcb = (FAR struct tcb_s *)sched_gettcb(pid);
  if (dtcb == NULL)
    {
      /* The pid does not correspond to any known thread.  The task
       * has probably already exited.
       */

      errcode = ESRCH;
      goto errout;
    }

  /* Only tasks and kernel threads can be deleted with this interface
   * (The semantics of the call should be sufficient to prohibit this).
   */

  DEBUGASSERT((dtcb->flags & TCB_FLAG_TTYPE_MASK) != TCB_FLAG_TTYPE_PTHREAD);

  /* Non-privileged tasks and pthreads may not delete privileged kernel
   * threads.
   *
   * REVISIT: We will need to look at this again in the future if/when
   * permissions are supported and a user task might also be privileged.
   */

  if (((rtcb->flags & TCB_FLAG_TTYPE_MASK) != TCB_FLAG_TTYPE_KERNEL) &&
      ((dtcb->flags & TCB_FLAG_TTYPE_MASK) == TCB_FLAG_TTYPE_KERNEL))
    {
      errcode = EACCES;
      goto errout;
    }

  /* Check to see if this task has the non-cancelable bit set in its
   * flags. Suppress context changes for a bit so that the flags are stable.
   * (the flags should not change in interrupt handling).
   */

  sched_lock();
  if ((dtcb->flags & TCB_FLAG_NONCANCELABLE) != 0)
    {
      /* Then we cannot cancel the thread now.  Here is how this is
       * supposed to work:
       *
       * "When cancellability is disabled, all cancels are held pending
       *  in the target thread until the thread changes the cancellability.
       *  When cancellability is deferred, all cancels are held pending in
       *  the target thread until the thread changes the cancellability,
       *  calls a function which is a cancellation point or calls
       *  pthread_testcancel(), thus creating a cancellation point. When
       *  cancellability is asynchronous, all cancels are acted upon
       *  immediately, interrupting the thread with its processing."
       */

      dtcb->flags |= TCB_FLAG_CANCEL_PENDING;
      sched_unlock();
      return OK;
    }

#ifdef CONFIG_CANCELLATION_POINTS
  /* Check if this task supports deferred cancellation */

  if ((dtcb->flags & TCB_FLAG_CANCEL_DEFERRED) != 0)
    {
      /* Then we cannot cancel the task asynchronously.  Mark the
       * cancellation as pending.
       */

      dtcb->flags |= TCB_FLAG_CANCEL_PENDING;

      /* If the task is waiting at a cancellation point, then notify of the
       * cancellation thereby waking the task up with an ECANCELED error.
       */

      if (dtcb->cpcount > 0)
        {
          nxnotify_cancellation(dtcb);
        }

      sched_unlock();
      return OK;
    }
#endif

  /* Check if the task to delete is the calling task */

  sched_unlock();
  if (pid == rtcb->pid)
    {
      /* If it is, then what we really wanted to do was exit. Note that we
       * don't bother to unlock the TCB since it will be going away.
       */

      exit(EXIT_SUCCESS);
    }

  /* Otherwise, perform the asynchronous cancellation, letting
   * nxtask_terminate() do all of the heavy lifting.
   */

  ret = nxtask_terminate(pid, false);
  if (ret < 0)
    {
      errcode = -ret;
      goto errout;
    }

  return OK;

errout:
  set_errno(errcode);
  return ERROR;
}