in amazon-freertos/lib/FreeRTOS/queue.c [1414:1629]
BaseType_t xQueueSemaphoreTake( QueueHandle_t xQueue, TickType_t xTicksToWait )
{
BaseType_t xEntryTimeSet = pdFALSE;
TimeOut_t xTimeOut;
Queue_t * const pxQueue = xQueue;
#if( configUSE_MUTEXES == 1 )
BaseType_t xInheritanceOccurred = pdFALSE;
#endif
/* Check the queue pointer is not NULL. */
configASSERT( ( pxQueue ) );
/* Check this really is a semaphore, in which case the item size will be
0. */
configASSERT( pxQueue->uxItemSize == 0 );
/* 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();
{
/* Semaphores are queues with an item size of 0, and where the
number of messages in the queue is the semaphore's count value. */
const UBaseType_t uxSemaphoreCount = 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( uxSemaphoreCount > ( UBaseType_t ) 0 )
{
traceQUEUE_RECEIVE( pxQueue );
/* Semaphores are queues with a data size of zero and where the
messages waiting is the semaphore's count. Reduce the count. */
pxQueue->uxMessagesWaiting = uxSemaphoreCount - ( UBaseType_t ) 1;
#if ( configUSE_MUTEXES == 1 )
{
if( pxQueue->uxQueueType == queueQUEUE_IS_MUTEX )
{
/* Record the information required to implement
priority inheritance should it become necessary. */
pxQueue->u.xSemaphore.xMutexHolder = pvTaskIncrementMutexHeldCount();
}
else
{
mtCOVERAGE_TEST_MARKER();
}
}
#endif /* configUSE_MUTEXES */
/* Check to see if other tasks are blocked waiting to give the
semaphore, and if so, unblock the highest priority such task. */
if( listLIST_IS_EMPTY( &( pxQueue->xTasksWaitingToSend ) ) == pdFALSE )
{
if( xTaskRemoveFromEventList( &( pxQueue->xTasksWaitingToSend ) ) != pdFALSE )
{
queueYIELD_IF_USING_PREEMPTION();
}
else
{
mtCOVERAGE_TEST_MARKER();
}
}
else
{
mtCOVERAGE_TEST_MARKER();
}
taskEXIT_CRITICAL();
return pdPASS;
}
else
{
if( xTicksToWait == ( TickType_t ) 0 )
{
/* For inheritance to have occurred there must have been an
initial timeout, and an adjusted timeout cannot become 0, as
if it were 0 the function would have exited. */
#if( configUSE_MUTEXES == 1 )
{
configASSERT( xInheritanceOccurred == pdFALSE );
}
#endif /* configUSE_MUTEXES */
/* The semaphore count was 0 and no block time is specified
(or the block time has expired) so exit now. */
taskEXIT_CRITICAL();
traceQUEUE_RECEIVE_FAILED( pxQueue );
return errQUEUE_EMPTY;
}
else if( xEntryTimeSet == pdFALSE )
{
/* The semaphore count was 0 and a block time was specified
so configure the timeout structure ready to block. */
vTaskInternalSetTimeOutState( &xTimeOut );
xEntryTimeSet = pdTRUE;
}
else
{
/* Entry time was already set. */
mtCOVERAGE_TEST_MARKER();
}
}
}
taskEXIT_CRITICAL();
/* Interrupts and other tasks can give to and take from the semaphore
now 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 )
{
/* A block time is specified and not expired. If the semaphore
count is 0 then enter the Blocked state to wait for a semaphore to
become available. As semaphores are implemented with queues the
queue being empty is equivalent to the semaphore count being 0. */
if( prvIsQueueEmpty( pxQueue ) != pdFALSE )
{
traceBLOCKING_ON_QUEUE_RECEIVE( pxQueue );
#if ( configUSE_MUTEXES == 1 )
{
if( pxQueue->uxQueueType == queueQUEUE_IS_MUTEX )
{
taskENTER_CRITICAL();
{
xInheritanceOccurred = xTaskPriorityInherit( pxQueue->u.xSemaphore.xMutexHolder );
}
taskEXIT_CRITICAL();
}
else
{
mtCOVERAGE_TEST_MARKER();
}
}
#endif
vTaskPlaceOnEventList( &( pxQueue->xTasksWaitingToReceive ), xTicksToWait );
prvUnlockQueue( pxQueue );
if( xTaskResumeAll() == pdFALSE )
{
portYIELD_WITHIN_API();
}
else
{
mtCOVERAGE_TEST_MARKER();
}
}
else
{
/* There was no timeout and the semaphore count was not 0, so
attempt to take the semaphore again. */
prvUnlockQueue( pxQueue );
( void ) xTaskResumeAll();
}
}
else
{
/* Timed out. */
prvUnlockQueue( pxQueue );
( void ) xTaskResumeAll();
/* If the semaphore count is 0 exit now as the timeout has
expired. Otherwise return to attempt to take the semaphore that is
known to be available. As semaphores are implemented by queues the
queue being empty is equivalent to the semaphore count being 0. */
if( prvIsQueueEmpty( pxQueue ) != pdFALSE )
{
#if ( configUSE_MUTEXES == 1 )
{
/* xInheritanceOccurred could only have be set if
pxQueue->uxQueueType == queueQUEUE_IS_MUTEX so no need to
test the mutex type again to check it is actually a mutex. */
if( xInheritanceOccurred != pdFALSE )
{
taskENTER_CRITICAL();
{
UBaseType_t uxHighestWaitingPriority;
/* This task blocking on the mutex caused another
task to inherit this task's priority. Now this task
has timed out the priority should be disinherited
again, but only as low as the next highest priority
task that is waiting for the same mutex. */
uxHighestWaitingPriority = prvGetDisinheritPriorityAfterTimeout( pxQueue );
vTaskPriorityDisinheritAfterTimeout( pxQueue->u.xSemaphore.xMutexHolder, uxHighestWaitingPriority );
}
taskEXIT_CRITICAL();
}
}
#endif /* configUSE_MUTEXES */
traceQUEUE_RECEIVE_FAILED( pxQueue );
return errQUEUE_EMPTY;
}
else
{
mtCOVERAGE_TEST_MARKER();
}
}
} /*lint -restore */
}