/************************************************************
* mq_receive.c
*
* Copyright (C) 2007 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 Gregory Nutt 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> /* uint32, etc. */
#include <stdarg.h> /* va_list */
#include <unistd.h>
#include <fcntl.h> /* O_NONBLOCK */
#include <string.h>
#include <assert.h>
#include <errno.h>
#include <mqueue.h>
#include <sched.h>
#include <debug.h>
#include <nuttx/kmalloc.h>
#include <nuttx/arch.h>
#include <nuttx/os_external.h>
#include "os_internal.h"
#include "sig_internal.h"
#include "mq_internal.h"
/************************************************************
* Definitions
************************************************************/
/************************************************************
* Private Type Declarations
************************************************************/
/************************************************************
* Global Variables
************************************************************/
/************************************************************
* Private Variables
************************************************************/
/************************************************************
* Private Functions
************************************************************/
/************************************************************
* Public Functions
************************************************************/
/************************************************************
* Function: mq_receive
*
* 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_receive 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_receive() will block until a message is added
* to the message queue. 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.
*
* If the queue is empty and O_NONBLOCK is set, ERROR will
* be returned.
*
* 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.
*
* 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'
*
* Assumptions:
*
************************************************************/
int mq_receive(mqd_t mqdes, void *msg, size_t msglen, int *prio)
{
FAR _TCB *rtcb;
FAR _TCB *btcb;
FAR msgq_t *msgq;
FAR mqmsg_t *curr;
irqstate_t saved_state;
ubyte rcvmsglen;
int ret = ERROR;
/* Verify the input parameters */
if (!msg || !mqdes)
{
*get_errno_ptr() = EINVAL;
return ERROR;
}
if ((mqdes->oflags & O_RDOK) == 0)
{
*get_errno_ptr() = EPERM;
return ERROR;
}
if (msglen < (size_t)mqdes->msgq->maxmsgsize)
{
*get_errno_ptr() = EMSGSIZE;
return ERROR;
}
/* Get a pointer to the message queue */
sched_lock();
msgq = mqdes->msgq;
/* Several operations must be performed below: We must determine if
* a message is pending and, if not, wait for the message. Since
* messages can be sent from the interrupt level, there is a race
* condition that can only be eliminated by disabling interrupts!
*/
saved_state = irqsave();
/* Get the message from the head of the queue */
while ((curr = (FAR mqmsg_t*)sq_remfirst(&msgq->msglist)) == NULL)
{
/* Should we block until there the above condition has been
* satisfied?
*/
if (!(mqdes->oflags & O_NONBLOCK))
{
/* Block and try again */
rtcb = (FAR _TCB*)g_readytorun.head;
rtcb->msgwaitq = msgq;
msgq->nwaitnotempty++;
*get_errno_ptr() = OK;
up_block_task(rtcb, TSTATE_WAIT_MQNOTEMPTY);
/* When we resume at this point, either (1) the message queue
* is no longer empty, or (2) the wait has been interrupted by
* a signal. We can detect the latter case be examining the
* errno value (should be EINTR).
*/
if (*get_errno_ptr() != OK)
{
break;
}
}
else
{
/* The queue was empty, and the O_NONBLOCK flag was set for the
* message queue description referred to by 'mqdes'.
*/
*get_errno_ptr() = EAGAIN;
break;
}
}
/* If we got message, then decrement the number of messages in
* the queue while we are still in the critical section
*/
if (curr)
{
msgq->nmsgs--;
}
irqrestore(saved_state);
/* Check (again) if we got a message from the message queue*/
if (curr)
{
/* Get the length of the message (also the return value) */
ret = rcvmsglen = curr->msglen;
/* Copy the message into the caller's buffer */
memcpy(msg, (const void*)curr->mail, rcvmsglen);
/* Copy the message priority as well (if a buffer is provided) */
if (prio)
{
*prio = curr->priority;
}
/* We are done with the message. Deallocate it now. */
mq_msgfree(curr);
/* Check if any tasks are waiting for the MQ not full event. */
if (msgq->nwaitnotfull > 0)
{
/* Find the highest priority task that is waiting for
* this queue to be not-full in g_waitingformqnotfull list.
* This must be performed in a critical section because
* messages can be sent from interrupt handlers.
*/
saved_state = irqsave();
for (btcb = (FAR _TCB*)g_waitingformqnotfull.head;
btcb && btcb->msgwaitq != msgq;
btcb = btcb->flink);
/* If one was found, unblock it. NOTE: There is a race
* condition here: the queue might be full again by the
* time the task is unblocked
*/
if (!btcb)
{
PANIC(OSERR_MQNOTFULLCOUNT);
}
else
{
btcb->msgwaitq = NULL;
msgq->nwaitnotfull--;
up_unblock_task(btcb);
}
irqrestore(saved_state);
}
}
sched_unlock();
return ret;
}
