queue.c

FreeRTOS source code as bundled with the book "Using FreeRTOS Real-Time Kernel - A Practical Approac

/*
	FreeRTOS.org V5.0.4 - Copyright (C) 2003-2008 Richard Barry.

	This file is part of the FreeRTOS.org distribution.

	FreeRTOS.org is free software; you can redistribute it and/or modify
	it under the terms of the GNU General Public License as published by
	the Free Software Foundation; either version 2 of the License, or
	(at your option) any later version.

	FreeRTOS.org is distributed in the hope that it will be useful,
	but WITHOUT ANY WARRANTY; without even the implied warranty of
	MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
	GNU General Public License for more details.

	You should have received a copy of the GNU General Public License
	along with FreeRTOS.org; if not, write to the Free Software
	Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307  USA

	A special exception to the GPL can be applied should you wish to distribute
	a combined work that includes FreeRTOS.org, without being obliged to provide
	the source code for any proprietary components.  See the licensing section
	of http://www.FreeRTOS.org for full details of how and when the exception
	can be applied.

    ***************************************************************************
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	Please ensure to read the configuration and relevant port sections of the
	online documentation.

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*/

#include <stdlib.h>
#include <string.h>
#include "FreeRTOS.h"
#include "task.h"
#include "croutine.h"

/*-----------------------------------------------------------
 * PUBLIC LIST API documented in list.h
 *----------------------------------------------------------*/

/* Constants used with the cRxLock and cTxLock structure members. */
#define queueUNLOCKED							( ( signed portBASE_TYPE ) -1 )
#define queueLOCKED_UNMODIFIED					( ( signed portBASE_TYPE ) 0 )

#define queueERRONEOUS_UNBLOCK					( -1 )

/* For internal use only. */
#define	queueSEND_TO_BACK	( 0 )
#define	queueSEND_TO_FRONT	( 1 )

/* Effectively make a union out of the xQUEUE structure. */
#define pxMutexHolder				pcTail
#define uxQueueType					pcHead
#define uxRecursiveCallCount		pcReadFrom
#define queueQUEUE_IS_MUTEX			NULL

/* Semaphores do not actually store or copy data, so have an items size of
zero. */
#define queueSEMAPHORE_QUEUE_ITEM_LENGTH ( 0 )
#define queueDONT_BLOCK					 ( ( portTickType ) 0 )
#define queueMUTEX_GIVE_BLOCK_TIME		 ( ( portTickType ) 0 )

/*
 * Definition of the queue used by the scheduler.
 * Items are queued by copy, not reference.
 */
typedef struct QueueDefinition
{
	signed portCHAR *pcHead;				/*< Points to the beginning of the queue storage area. */
	signed portCHAR *pcTail;				/*< Points to the byte at the end of the queue storage area.  Once more byte is allocated than necessary to store the queue items, this is used as a marker. */

	signed portCHAR *pcWriteTo;				/*< Points to the free next place in the storage area. */
	signed portCHAR *pcReadFrom;			/*< Points to the last place that a queued item was read from. */

	xList xTasksWaitingToSend;				/*< List of tasks that are blocked waiting to post onto this queue.  Stored in priority order. */
	xList xTasksWaitingToReceive;			/*< List of tasks that are blocked waiting to read from this queue.  Stored in priority order. */

	volatile unsigned portBASE_TYPE uxMessagesWaiting;/*< The number of items currently in the queue. */
	unsigned portBASE_TYPE uxLength;		/*< The length of the queue defined as the number of items it will hold, not the number of bytes. */
	unsigned portBASE_TYPE uxItemSize;		/*< The size of each items that the queue will hold. */

	signed portBASE_TYPE xRxLock;			/*< Stores the number of items received from the queue (removed from the queue) while the queue was locked.  Set to queueUNLOCKED when the queue is not locked. */
	signed portBASE_TYPE xTxLock;			/*< Stores the number of items transmitted to the queue (added to the queue) while the queue was locked.  Set to queueUNLOCKED when the queue is not locked. */

} xQUEUE;
/*-----------------------------------------------------------*/

/*
 * Inside this file xQueueHandle is a pointer to a xQUEUE structure.
 * To keep the definition private the API header file defines it as a
 * pointer to void.
 */
typedef xQUEUE * xQueueHandle;

/*
 * Prototypes for public functions are included here so we don't have to
 * include the API header file (as it defines xQueueHandle differently).  These
 * functions are documented in the API header file.
 */
xQueueHandle xQueueCreate( unsigned portBASE_TYPE uxQueueLength, unsigned portBASE_TYPE uxItemSize );
signed portBASE_TYPE xQueueGenericSend( xQueueHandle xQueue, const void * const pvItemToQueue, portTickType xTicksToWait, portBASE_TYPE xCopyPosition );
unsigned portBASE_TYPE uxQueueMessagesWaiting( const xQueueHandle pxQueue );
void vQueueDelete( xQueueHandle xQueue );
signed portBASE_TYPE xQueueGenericSendFromISR( xQueueHandle pxQueue, const void * const pvItemToQueue, signed portBASE_TYPE *pxHigherPriorityTaskWoken, portBASE_TYPE xCopyPosition );
signed portBASE_TYPE xQueueGenericReceive( xQueueHandle pxQueue, void * const pvBuffer, portTickType xTicksToWait, portBASE_TYPE xJustPeeking );
signed portBASE_TYPE xQueueReceiveFromISR( xQueueHandle pxQueue, void * const pvBuffer, signed portBASE_TYPE *pxTaskWoken );
xQueueHandle xQueueCreateMutex( void );
xQueueHandle xQueueCreateCountingSemaphore( unsigned portBASE_TYPE uxCountValue, unsigned portBASE_TYPE uxInitialCount );
portBASE_TYPE xQueueTakeMutexRecursive( xQueueHandle xMutex, portTickType xBlockTime );
portBASE_TYPE xQueueGiveMutexRecursive( xQueueHandle xMutex );
signed portBASE_TYPE xQueueAltGenericSend( xQueueHandle pxQueue, const void * const pvItemToQueue, portTickType xTicksToWait, portBASE_TYPE xCopyPosition );
signed portBASE_TYPE xQueueAltGenericReceive( xQueueHandle pxQueue, void * const pvBuffer, portTickType xTicksToWait, portBASE_TYPE xJustPeeking );
signed portBASE_TYPE xQueueIsQueueEmptyFromISR( const xQueueHandle pxQueue );
signed portBASE_TYPE xQueueIsQueueFullFromISR( const xQueueHandle pxQueue );
unsigned portBASE_TYPE uxQueueMessagesWaitingFromISR( const xQueueHandle pxQueue );

/*
 * Co-routine queue functions differ from task queue functions.  Co-routines are
 * an optional component.
 */
#if configUSE_CO_ROUTINES == 1
	signed portBASE_TYPE xQueueCRSendFromISR( xQueueHandle pxQueue, const void *pvItemToQueue, signed portBASE_TYPE xCoRoutinePreviouslyWoken );
	signed portBASE_TYPE xQueueCRReceiveFromISR( xQueueHandle pxQueue, void *pvBuffer, signed portBASE_TYPE *pxTaskWoken );
	signed portBASE_TYPE xQueueCRSend( xQueueHandle pxQueue, const void *pvItemToQueue, portTickType xTicksToWait );
	signed portBASE_TYPE xQueueCRReceive( xQueueHandle pxQueue, void *pvBuffer, portTickType xTicksToWait );
#endif

/*
 * The queue registry is just a means for kernel aware debuggers to locate
 * queue structures.  It has no other purpose so is an optional component.
 */
#if configQUEUE_REGISTRY_SIZE > 0

	/* The type stored within the queue registry array.  This allows a name
	to be assigned to each queue making kernel aware debugging a little
	more user friendly. */
	typedef struct QUEUE_REGISTRY_ITEM
	{
		signed portCHAR *pcQueueName;
		xQueueHandle xHandle;
	} xQueueRegistryItem;

	/* The queue registry is simply an array of xQueueRegistryItem structures.
	The pcQueueName member of a structure being NULL is indicative of the
	array position being vacant. */
	xQueueRegistryItem xQueueRegistry[ configQUEUE_REGISTRY_SIZE ];

	/* Removes a queue from the registry by simply setting the pcQueueName
	member to NULL. */
	static void vQueueUnregisterQueue( xQueueHandle xQueue );
	void vQueueAddToRegistry( xQueueHandle xQueue, signed portCHAR *pcQueueName );
#endif

/*
 * Unlocks a queue locked by a call to prvLockQueue.  Locking a queue does not
 * prevent an ISR from adding or removing items to the queue, but does prevent
 * an ISR from removing tasks from the queue event lists.  If an ISR finds a
 * queue is locked it will instead increment the appropriate queue lock count
 * to indicate that a task may require unblocking.  When the queue in unlocked
 * these lock counts are inspected, and the appropriate action taken.
 */
static void prvUnlockQueue( xQueueHandle pxQueue );

/*
 * Uses a critical section to determine if there is any data in a queue.
 *
 * @return pdTRUE if the queue contains no items, otherwise pdFALSE.
 */
static signed portBASE_TYPE prvIsQueueEmpty( const xQueueHandle pxQueue );

/*
 * Uses a critical section to determine if there is any space in a queue.
 *
 * @return pdTRUE if there is no space, otherwise pdFALSE;
 */
static signed portBASE_TYPE prvIsQueueFull( const xQueueHandle pxQueue );

/*
 * Copies an item into the queue, either at the front of the queue or the
 * back of the queue.
 */
static void prvCopyDataToQueue( xQUEUE *pxQueue, const void *pvItemToQueue, portBASE_TYPE xPosition );

/*
 * Copies an item out of a queue.
 */
static void prvCopyDataFromQueue( xQUEUE * const pxQueue, const void *pvBuffer );
/*-----------------------------------------------------------*/

/*
 * Macro to mark a queue as locked.  Locking a queue prevents an ISR from
 * accessing the queue event lists.
 */
#define prvLockQueue( pxQueue )							\
{														\
	taskENTER_CRITICAL();								\
	{													\
		if( pxQueue->xRxLock == queueUNLOCKED )			\
		{												\
			pxQueue->xRxLock = queueLOCKED_UNMODIFIED;	\
		}												\
		if( pxQueue->xTxLock == queueUNLOCKED )			\
		{												\
			pxQueue->xTxLock = queueLOCKED_UNMODIFIED;	\
		}												\
	}													\
	taskEXIT_CRITICAL();								\
}
/*-----------------------------------------------------------*/


/*-----------------------------------------------------------
 * PUBLIC QUEUE MANAGEMENT API documented in queue.h
 *----------------------------------------------------------*/

xQueueHandle xQueueCreate( unsigned portBASE_TYPE uxQueueLength, unsigned portBASE_TYPE uxItemSize )
{
xQUEUE *pxNewQueue;
size_t xQueueSizeInBytes;

	/* Allocate the new queue structure. */
	if( uxQueueLength > ( unsigned portBASE_TYPE ) 0 )
	{
		pxNewQueue = ( xQUEUE * ) pvPortMalloc( sizeof( xQUEUE ) );
		if( pxNewQueue != NULL )
		{
			/* Create the list of pointers to queue items.  The queue is one byte
			longer than asked for to make wrap checking easier/faster. */
			xQueueSizeInBytes = ( size_t ) ( uxQueueLength * uxItemSize ) + ( size_t ) 1;

			pxNewQueue->pcHead = ( signed portCHAR * ) pvPortMalloc( xQueueSizeInBytes );
			if( pxNewQueue->pcHead != NULL )
			{
				/* Initialise the queue members as described above where the
				queue type is defined. */
				pxNewQueue->pcTail = pxNewQueue->pcHead + ( uxQueueLength * uxItemSize );
				pxNewQueue->uxMessagesWaiting = 0;
				pxNewQueue->pcWriteTo = pxNewQueue->pcHead;
				pxNewQueue->pcReadFrom = pxNewQueue->pcHead + ( ( uxQueueLength - 1 ) * uxItemSize );
				pxNewQueue->uxLength = uxQueueLength;
				pxNewQueue->uxItemSize = uxItemSize;
				pxNewQueue->xRxLock = queueUNLOCKED;
				pxNewQueue->xTxLock = queueUNLOCKED;

				/* Likewise ensure the event queues start with the correct state. */
				vListInitialise( &( pxNewQueue->xTasksWaitingToSend ) );
				vListInitialise( &( pxNewQueue->xTasksWaitingToReceive ) );

				traceQUEUE_CREATE( pxNewQueue );

				return  pxNewQueue;
			}
			else
			{
				traceQUEUE_CREATE_FAILED();
				vPortFree( pxNewQueue );
			}
		}
	}

	/* Will only reach here if we could not allocate enough memory or no memory
	was required. */
	return NULL;
}
/*-----------------------------------------------------------*/

#if ( configUSE_MUTEXES == 1 )

	xQueueHandle xQueueCreateMutex( void )
	{
	xQUEUE *pxNewQueue;

		/* Allocate the new queue structure. */
		pxNewQueue = ( xQUEUE * ) pvPortMalloc( sizeof( xQUEUE ) );
		if( pxNewQueue != NULL )
		{
			/* Information required for priority inheritance. */
			pxNewQueue->pxMutexHolder = NULL;
			pxNewQueue->uxQueueType = queueQUEUE_IS_MUTEX;

			/* Queues used as a mutex no data is actually copied into or out
			of the queue. */
			pxNewQueue->pcWriteTo = NULL;
			pxNewQueue->pcReadFrom = NULL;

			/* Each mutex has a length of 1 (like a binary semaphore) and
			an item size of 0 as nothing is actually copied into or out
			of the mutex. */
			pxNewQueue->uxMessagesWaiting = 0;
			pxNewQueue->uxLength = 1;
			pxNewQueue->uxItemSize = 0;
			pxNewQueue->xRxLock = queueUNLOCKED;
			pxNewQueue->xTxLock = queueUNLOCKED;

			/* Ensure the event queues start with the correct state. */
			vListInitialise( &( pxNewQueue->xTasksWaitingToSend ) );
			vListInitialise( &( pxNewQueue->xTasksWaitingToReceive ) );

			/* Start with the semaphore in the expected state. */
			xQueueGenericSend( pxNewQueue, NULL, 0, queueSEND_TO_BACK );

			traceCREATE_MUTEX( pxNewQueue );
		}
		else
		{
			traceCREATE_MUTEX_FAILED();
		}

		return pxNewQueue;
	}

#endif /* configUSE_MUTEXES */
/*-----------------------------------------------------------*/

#if configUSE_RECURSIVE_MUTEXES == 1

	portBASE_TYPE xQueueGiveMutexRecursive( xQueueHandle pxMutex )
	{
	portBASE_TYPE xReturn;

		/* If this is the task that holds the mutex then pxMutexHolder will not
		change outside of this task.  If this task does not hold the mutex then
		pxMutexHolder can never coincidentally equal the tasks handle, and as
		this is the only condition we are interested in it does not matter if
		pxMutexHolder is accessed simultaneously by another task.  Therefore no
		mutual exclusion is required to test the pxMutexHolder variable. */
		if( pxMutex->pxMutexHolder == xTaskGetCurrentTaskHandle() )
		{
			traceGIVE_MUTEX_RECURSIVE( pxMutex );

			/* uxRecursiveCallCount cannot be zero if pxMutexHolder is equal to
			the task handle, therefore no underflow check is required.  Also,
			uxRecursiveCallCount is only modified by the mutex holder, and as
			there can only be one, no mutual exclusion is required to modify the
			uxRecursiveCallCount member. */
			( pxMutex->uxRecursiveCallCount )--;

			/* Have we unwound the call count? */
			if( pxMutex->uxRecursiveCallCount == 0 )
			{
				/* Return the mutex.  This will automatically unblock any other
				task that might be waiting to access the mutex. */
                xQueueGenericSend( pxMutex, NULL, queueMUTEX_GIVE_BLOCK_TIME, queueSEND_TO_BACK );
			}

			xReturn = pdPASS;
		}
		else
		{
			/* We cannot give the mutex because we are not the holder. */
			xReturn = pdFAIL;

			traceGIVE_MUTEX_RECURSIVE_FAILED( pxMutex );
		}

		return xReturn;
	}

#endif /* configUSE_RECURSIVE_MUTEXES */
/*-----------------------------------------------------------*/

#if configUSE_RECURSIVE_MUTEXES == 1

	portBASE_TYPE xQueueTakeMutexRecursive( xQueueHandle pxMutex, portTickType xBlockTime )
	{
	portBASE_TYPE xReturn;