nuttx/sched/semaphore/sem_waitirq.c

/****************************************************************************
 * sched/semaphore/sem_waitirq.c
 *
 *   Copyright (C) 2007-2010, 2014 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,
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 ****************************************************************************/

/****************************************************************************
 * Included Files
 ****************************************************************************/

#include <nuttx/config.h>

#include <sched.h>
#include <errno.h>
#include <nuttx/arch.h>

#include "semaphore/semaphore.h"

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

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

/****************************************************************************
 * Global Variables
 ****************************************************************************/

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

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

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

/****************************************************************************
 * Name: sem_waitirq
 *
 * Description:
 *   This function is called when either:
 *
 *   1. A signal is received by a task that is waiting on a semaphore.
 *      According to the POSIX spec, "...the calling thread shall not return
 *      from the call to [sem_wait] until it either locks the semaphore or
 *      the call is interrupted by a signal."
 *   2. From logic associated with sem_timedwait().  This function is called
 *      when the timeout elapses without receiving the semaphore.
 *
 * Parameters:
 *   wtcb    - A pointer to the TCB of the task that is waiting on a
 *             semphaphore, but has received a signal or timeout instead.
 *   errcode - EINTR if the semaphore wait was awakened by a signal;
 *             ETIMEDOUT if awakened by a timeout
 *
 * Return Value:
 *   None
 *
 * Assumptions:
 *
 ****************************************************************************/

void sem_waitirq(FAR struct tcb_s *wtcb, int errcode)
{
  irqstate_t saved_state;

  /* Disable interrupts.  This is necessary (unfortunately) because an
   * interrupt handler may attempt to post the semaphore while we are
   * doing this.
   */

  saved_state = irqsave();

  /* It is possible that an interrupt/context switch beat us to the punch
   * and already changed the task's state.
   */

  if (wtcb->task_state == TSTATE_WAIT_SEM)
    {
      sem_t *sem = wtcb->waitsem;
      DEBUGASSERT(sem != NULL && sem->semcount < 0);

      /* Restore the correct priority of all threads that hold references
       * to this semaphore.
       */

      sem_canceled(wtcb, sem);

      /* And increment the count on the semaphore.  This releases the count
       * that was taken by sem_post().  This count decremented the semaphore
       * count to negative and caused the thread to be blocked in the first
       * place.
       */

      sem->semcount++;

      /* Indicate that the semaphore wait is over. */

      wtcb->waitsem = NULL;

      /* Mark the errno value for the thread. */

      wtcb->pterrno = errcode;

      /* Restart the task. */

      up_unblock_task(wtcb);
    }

  /* Interrupts may now be enabled. */

  irqrestore(saved_state);
}