in queue.c [1740:1888]
BaseType_t xQueuePeek( QueueHandle_t xQueue,
void * const pvBuffer,
TickType_t xTicksToWait )
{
BaseType_t xEntryTimeSet = pdFALSE;
TimeOut_t xTimeOut;
int8_t * pcOriginalReadPosition;
Queue_t * const pxQueue = xQueue;
/* Check the pointer is not NULL. */
configASSERT( ( pxQueue ) );
/* The buffer into which data is received can only be NULL if the data size
* is zero (so no data is copied into the buffer. */
configASSERT( !( ( ( pvBuffer ) == NULL ) && ( ( pxQueue )->uxItemSize != ( UBaseType_t ) 0U ) ) );
/* Cannot block if the scheduler is suspended. */
#if ( ( INCLUDE_xTaskGetSchedulerState == 1 ) || ( configUSE_TIMERS == 1 ) )
{
configASSERT( !( ( xTaskGetSchedulerState() == taskSCHEDULER_SUSPENDED ) && ( xTicksToWait != 0 ) ) );
}
#endif
/*lint -save -e904 This function relaxes the coding standard somewhat to
* allow return statements within the function itself. This is done in the
* interest of execution time efficiency. */
for( ; ; )
{
taskENTER_CRITICAL();
{
const UBaseType_t uxMessagesWaiting = pxQueue->uxMessagesWaiting;
/* Is there data in the queue now? To be running the calling task
* must be the highest priority task wanting to access the queue. */
if( uxMessagesWaiting > ( UBaseType_t ) 0 )
{
/* Remember the read position so it can be reset after the data
* is read from the queue as this function is only peeking the
* data, not removing it. */
pcOriginalReadPosition = pxQueue->u.xQueue.pcReadFrom;
prvCopyDataFromQueue( pxQueue, pvBuffer );
traceQUEUE_PEEK( pxQueue );
/* The data is not being removed, so reset the read pointer. */
pxQueue->u.xQueue.pcReadFrom = pcOriginalReadPosition;
/* The data is being left in the queue, so see if there are
* any other tasks waiting for the data. */
if( listLIST_IS_EMPTY( &( pxQueue->xTasksWaitingToReceive ) ) == pdFALSE )
{
if( xTaskRemoveFromEventList( &( pxQueue->xTasksWaitingToReceive ) ) != pdFALSE )
{
/* The task waiting has a higher priority than this task. */
queueYIELD_IF_USING_PREEMPTION();
}
else
{
mtCOVERAGE_TEST_MARKER();
}
}
else
{
mtCOVERAGE_TEST_MARKER();
}
taskEXIT_CRITICAL();
return pdPASS;
}
else
{
if( xTicksToWait == ( TickType_t ) 0 )
{
/* The queue was empty and no block time is specified (or
* the block time has expired) so leave now. */
taskEXIT_CRITICAL();
traceQUEUE_PEEK_FAILED( pxQueue );
return errQUEUE_EMPTY;
}
else if( xEntryTimeSet == pdFALSE )
{
/* The queue was empty and a block time was specified so
* configure the timeout structure ready to enter the blocked
* state. */
vTaskInternalSetTimeOutState( &xTimeOut );
xEntryTimeSet = pdTRUE;
}
else
{
/* Entry time was already set. */
mtCOVERAGE_TEST_MARKER();
}
}
}
taskEXIT_CRITICAL();
/* Interrupts and other tasks can send to and receive from the queue
* now that the critical section has been exited. */
vTaskSuspendAll();
prvLockQueue( pxQueue );
/* Update the timeout state to see if it has expired yet. */
if( xTaskCheckForTimeOut( &xTimeOut, &xTicksToWait ) == pdFALSE )
{
/* Timeout has not expired yet, check to see if there is data in the
* queue now, and if not enter the Blocked state to wait for data. */
if( prvIsQueueEmpty( pxQueue ) != pdFALSE )
{
traceBLOCKING_ON_QUEUE_PEEK( pxQueue );
vTaskPlaceOnEventList( &( pxQueue->xTasksWaitingToReceive ), xTicksToWait );
prvUnlockQueue( pxQueue );
if( xTaskResumeAll() == pdFALSE )
{
portYIELD_WITHIN_API();
}
else
{
mtCOVERAGE_TEST_MARKER();
}
}
else
{
/* There is data in the queue now, so don't enter the blocked
* state, instead return to try and obtain the data. */
prvUnlockQueue( pxQueue );
( void ) xTaskResumeAll();
}
}
else
{
/* The timeout has expired. If there is still no data in the queue
* exit, otherwise go back and try to read the data again. */
prvUnlockQueue( pxQueue );
( void ) xTaskResumeAll();
if( prvIsQueueEmpty( pxQueue ) != pdFALSE )
{
traceQUEUE_PEEK_FAILED( pxQueue );
return errQUEUE_EMPTY;
}
else
{
mtCOVERAGE_TEST_MARKER();
}
}
} /*lint -restore */
}