/****************************************************************************
 * sched/task/task_exit.c
 *
 *   Copyright (C) 2008-2009, 2012-2014, 2016, 2018 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  "sched/sched.h"

#ifndef CONFIG_DISABLE_SIGNALS
#  include "signal/signal.h"
#endif
#include "task/task.h"

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

/****************************************************************************
 * Name: task_exit
 *
 * Description:
 *   This is a part of the logic used to implement _exit().  The full
 *   implementation of _exit() is architecture-dependent. The _exit()
 *   function also implements the bottom half of exit() and pthread_exit().
 *
 *   This function causes the currently running task (i.e., the task at the
 *   head of the ready-to-run list) to cease to exist.  This function should
 *   never be called from normal user code, but only from the architecture-
 *   specific implementation of exit.
 *
 *   Threads/tasks could also be terminated via pthread_cancel, task_delete(),
 *   and task_restart().  In the last two cases, the task will be terminated
 *   as though exit() were called.
 *
 * Input Parameters:
 *   None
 *
 * Returned Value:
 *   OK on success; or ERROR on failure
 *
 * Assumeptions:
 *   Executing within a critical section established by the caller.
 *
 ****************************************************************************/

int task_exit(void)
{
  FAR struct tcb_s *dtcb;
  FAR struct tcb_s *rtcb;
  int ret;
#ifdef CONFIG_SMP
  int cpu;

  /* Get the current CPU.  By assumption, we are within a critical section
   * and, hence, the CPU index will remain stable.
   *
   * Avoid using this_task() because it may assume a state that is not
   * appropriate for an exiting task.
   */

  cpu  = this_cpu();
  dtcb = current_task(cpu);
#else
  dtcb = this_task();
#endif

  /* Remove the TCB of the current task from the ready-to-run list.  A context
   * switch will definitely be necessary -- that must be done by the
   * architecture-specific logic.
   *
   * sched_removereadytorun will mark the task at the head of the ready-to-run
   * with state == TSTATE_TASK_RUNNING
   */

  (void)sched_removereadytorun(dtcb);

  /* Get the new task at the head of the ready to run list */

#ifdef CONFIG_SMP
  rtcb = current_task(cpu);
#else
  rtcb = this_task();
#endif

#ifdef CONFIG_SMP
  /* Because clearing the global IRQ control in sched_removereadytorun()
   * was moved to sched_resume_scheduler(). So call the API here.
   */

  sched_resume_scheduler(rtcb);
#endif

  /* We are now in a bad state -- the head of the ready to run task list
   * does not correspond to the thread that is running.  Disabling pre-
   * emption on this TCB and marking the new ready-to-run task as not
   * running (see, for example, get_errno_ptr()).
   *
   * We disable pre-emption here by directly incrementing the lockcount
   * (vs. calling sched_lock()).
   */

  rtcb->lockcount++;

#ifdef CONFIG_SMP
  /* Make sure that the system knows about the locked state */

  spin_setbit(&g_cpu_lockset, this_cpu(), &g_cpu_locksetlock,
              &g_cpu_schedlock);
#endif

  rtcb->task_state = TSTATE_TASK_READYTORUN;

  /* Move the TCB to the specified blocked task list and delete it.  Calling
   * task_terminate with non-blocking true will suppress atexit() and on-exit()
   * calls and will cause buffered I/O to fail to be flushed.  The former
   * is required _exit() behavior; the latter is optional _exit() behavior.
   */

  sched_addblocked(dtcb, TSTATE_TASK_INACTIVE);
  ret = task_terminate(dtcb->pid, true);
  rtcb->task_state = TSTATE_TASK_RUNNING;

  /* Decrement the lockcount on rctb. */

  rtcb->lockcount--;

#ifdef CONFIG_SMP
  if (rtcb->lockcount == 0)
    {
      /* Make sure that the system knows about the unlocked state */

      spin_clrbit(&g_cpu_lockset, this_cpu(), &g_cpu_locksetlock,
                  &g_cpu_schedlock);
    }
#endif

  /* If there are any pending tasks, then add them to the ready-to-run
   * task list now
   */

  if (g_pendingtasks.head != NULL)
    {
      (void)sched_mergepending();
    }

  return ret;
}