nuttx/sched/mq_timedreceive.c

/****************************************************************************
 * sched/mq_timedreceive.c
 *
 *   Copyright (C) 2007, 2008 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 <sys/types.h>
#include <unistd.h>
#include <errno.h>
#include <mqueue.h>
#include <wdog.h>
#include <debug.h>
#include <nuttx/arch.h>
#include "os_internal.h"
#include "clock_internal.h"
#include "mq_internal.h"

/****************************************************************************
 * Definitions
 ****************************************************************************/

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

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

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

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

/****************************************************************************
 * Function:  mq_rcvtimeout
 *
 * Description:
 *   This function is called if the timeout elapses before the message queue
 *   becomes non-empty.
 *
 * Parameters:
 *   argc  - the number of arguments (should be 1)
 *   pid   - the task ID of the task to wakeup
 *
 * Return Value:
 *   None
 *
 * Assumptions:
 *
 ****************************************************************************/

static void mq_rcvtimeout(int argc, uint32 pid)
{
  FAR _TCB *wtcb;
  irqstate_t saved_state;

  /* Disable interrupts.  This is necessary because an
   * interrupt handler may attempt to send a message while we are
   * doing this.
   */

  saved_state = irqsave();

  /* Get the TCB associated with this pid.  It is possible that
   * task may no longer be active when this watchdog goes off.
   */

  wtcb = sched_gettcb((pid_t)pid);

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

  if (wtcb && wtcb->task_state == TSTATE_WAIT_MQNOTEMPTY)
    {
      /* Mark the errno value for the thread. */

      wtcb->pterrno = ETIMEDOUT;

      /* Restart the the task. */

      up_unblock_task(wtcb);
    }

  /* Interrupts may now be enabled. */

  irqrestore(saved_state);
}

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

/****************************************************************************
 * Function:  mq_timedreceive
 *
 * Description:
 *   This function receives the oldest of the highest
 *   priority messages from the message queue specified by
 *   "mqdes."  If the size of the buffer in bytes (msglen) is
 *   less than the "mq_msgsize" attribute of the message
 *   queue, mq_timedreceive will return an error.  Otherwise, the
 *   selected message is removed from the queue and copied to
 *   "msg."
 *
 *   If the message queue is empty and O_NONBLOCK was not
 *   set, mq_timedreceive() will block until a message is added
 *   to the message queue (or until a timeout occurs).  If more
 *   than one task is waiting  to receive a message, only the
 *   task with the highest priority that has waited the longest
 *   will be unblocked.
 *
 *   mq_timedreceive() behaves just like mq_receive(), except
 *   that if the queue is empty and the O_NONBLOCK flag is not
 *   enabled for the message queue description, then abstime
 *   points to a structure which specifies a ceiling on the time
 *   for which the call will block.  This ceiling is an absolute
 *   timeout in seconds and nanoseconds since the Epoch (midnight
 *   on the morning of 1 January 1970).
 *
 *   If no message is available, and the timeout has already
 *   expired by the time of the call, mq_timedreceive() returns
 *   immediately.
 *
 * Parameters:
 *   mqdes - Message Queue Descriptor
 *   msg - Buffer to receive the message
 *   msglen - Size of the buffer in bytes
 *   prio - If not NULL, the location to store message priority.
 *   abstime - the absolute time to wait until a timeout is declared.
 *
 * Return Value:
 *   One success, the length of the selected message in bytes.is
 *   returned.  On failure, -1 (ERROR) is returned and the errno
 *   is set appropriately:
 *
 *   EAGAIN    The queue was empty, and the O_NONBLOCK flag was set
 *             for the message queue description referred to by 'mqdes'.
 *   EPERM     Message queue opened not opened for reading.
 *   EMSGSIZE  'msglen' was less than the maxmsgsize attribute of the
 *             message queue.
 *   EINTR     The call was interrupted by a signal handler.
 *   EINVAL    Invalid 'msg' or 'mqdes' or 'abstime'
 *   ETIMEDOUT The call timed out before a message could be transferred.
 *
 * Assumptions:
 *
 ****************************************************************************/

ssize_t mq_timedreceive(mqd_t mqdes, void *msg, size_t msglen,
                        int *prio, const struct timespec *abstime)
{
  WDOG_ID      wdog;
  FAR mqmsg_t *mqmsg;
  irqstate_t   saved_state;
  int          ret = ERROR;

  DEBUGASSERT(up_interrupt_context() == FALSE);

  /* Verify the input parameters and, in case of an error, set
   * errno appropriately.
   */

  if (mq_verifyreceive(mqdes, msg, msglen) != OK)
    {
      return ERROR;
    }

  if (!abstime || abstime->tv_sec < 0 || abstime->tv_nsec > 1000000000)
    {
      *get_errno_ptr() = EINVAL;
      return ERROR;
    }

  /* Create a watchdog.  We will not actually need this watchdog
   * unless the queue is not empty, but we will reserve it up front
   * before we enter the following critical section.
   */

  wdog = wd_create();
  if (!wdog)
    {
      *get_errno_ptr() = EINVAL;
      return ERROR;
    }

  /* Get the next mesage from the message queue.  We will disable
   * pre-emption until we have completed the message received.  This
   * is not too bad because if the receipt takes a long time, it will
   * be because we are blocked waiting for a message and pre-emption
   * will be re-enabled while we are blocked
   */

  sched_lock();

  /* Furthermore, mq_waitreceive() expects to have interrupts disabled
   * because messages can be sent from interrupt level.
   */

  saved_state = irqsave();

  /* Check if the message queue is empty.  If it is NOT empty, then we
   * will not need to start timer.
   */

  if (mqdes->msgq->msglist.head == NULL)
    {
      int ticks;

      /* Convert the timespec to clock ticks.  We must have interrupts
       * disabled here so that this time stays valid until the wait begins.
       */

      int result = clock_abstime2ticks(CLOCK_REALTIME, abstime, &ticks);

      /* If the time has already expired and the message queue is empty,
       * return immediately.
       */

      if (result == OK && ticks <= 0)
        {
          result = ETIMEDOUT;
        }

      /* Handle any time-related errors */

      if (result != OK)
        {
          *get_errno_ptr() = result;
          irqrestore(saved_state);
          sched_unlock();
          wd_delete(wdog);
          return ERROR;
        }

      /* Start the watchdog */

      wd_start(wdog, ticks, (wdentry_t)mq_rcvtimeout, 1, getpid());
    }

  /* Get the message from the message queue */

  mqmsg = mq_waitreceive(mqdes);

  /* Stop the watchdog timer (this is not harmful in the case where
   * it was never started)
   */

  wd_cancel(wdog);

  /* We can now restore interrupts */

  irqrestore(saved_state);

  /* Check if we got a message from the message queue.  We might
   * not have a message if:
   *
   * - The message queue is empty and O_NONBLOCK is set in the mqdes
   * - The wait was interrupted by a signal
   * - The watchdog timeout expired
   */

  if (mqmsg)
    {
      ret = mq_doreceive(mqdes, mqmsg, msg, prio);
    }

  sched_unlock();
  wd_delete(wdog);
  return ret;
}