heap_4.c

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*/

/*
 * A sample implementation of pvPortMalloc() and vPortFree() that combines
 * (coalescences) adjacent memory blocks as they are freed, and in so doing
 * limits memory fragmentation.
 *
 * See heap_1.c, heap_2.c and heap_3.c for alternative implementations, and the
 * memory management pages of http://www.FreeRTOS.org for more information.
 */
#include <stdlib.h>

/* Defining MPU_WRAPPERS_INCLUDED_FROM_API_FILE prevents task.h from redefining
all the API functions to use the MPU wrappers.  That should only be done when
task.h is included from an application file. */
#define MPU_WRAPPERS_INCLUDED_FROM_API_FILE

#include "FreeRTOS.h"
#include "task.h"

#undef MPU_WRAPPERS_INCLUDED_FROM_API_FILE

#if( configSUPPORT_DYNAMIC_ALLOCATION == 0 )
        #error This file must not be used if configSUPPORT_DYNAMIC_ALLOCATION is 0
#endif

/* Block sizes must not get too small. */
#define heapMINIMUM_BLOCK_SIZE  ( ( size_t ) ( xHeapStructSize << 1 ) )

/* Assumes 8bit bytes! */
#define heapBITS_PER_BYTE               ( ( size_t ) 8 )

/* Allocate the memory for the heap. */
#if( configAPPLICATION_ALLOCATED_HEAP == 1 )
        /* The application writer has already defined the array used for the RTOS
        heap - probably so it can be placed in a special segment or address. */
        extern uint8_t ucHeap[ configTOTAL_HEAP_SIZE ];
#else
        static uint8_t ucHeap[ configTOTAL_HEAP_SIZE ];
#endif /* configAPPLICATION_ALLOCATED_HEAP */

/* Define the linked list structure.  This is used to link free blocks in order
of their memory address. */
typedef struct A_BLOCK_LINK
{
        struct A_BLOCK_LINK *pxNextFreeBlock;   /*<< The next free block in the list. */
        size_t xBlockSize;                                              /*<< The size of the free block. */
} BlockLink_t;

/*-----------------------------------------------------------*/

/*
 * Inserts a block of memory that is being freed into the correct position in
 * the list of free memory blocks.  The block being freed will be merged with
 * the block in front it and/or the block behind it if the memory blocks are
 * adjacent to each other.
 */
static void prvInsertBlockIntoFreeList( BlockLink_t *pxBlockToInsert );

/*
 * Called automatically to setup the required heap structures the first time
 * pvPortMalloc() is called.
 */
static void prvHeapInit( void );

/*-----------------------------------------------------------*/

/* The size of the structure placed at the beginning of each allocated memory
block must by correctly byte aligned. */
static const size_t xHeapStructSize     = ( sizeof( BlockLink_t ) + ( ( size_t ) ( portBYTE_ALIGNMENT - 1 ) ) ) & ~( ( size_t ) portBYTE_ALIGNMENT_MASK );

/* Create a couple of list links to mark the start and end of the list. */
static BlockLink_t xStart, *pxEnd = NULL;

/* Keeps track of the number of free bytes remaining, but says nothing about
fragmentation. */
static size_t xFreeBytesRemaining = 0U;
static size_t xMinimumEverFreeBytesRemaining = 0U;

/* Gets set to the top bit of an size_t type.  When this bit in the xBlockSize
member of an BlockLink_t structure is set then the block belongs to the
application.  When the bit is free the block is still part of the free heap
space. */
static size_t xBlockAllocatedBit = 0;

/*-----------------------------------------------------------*/

void *pvPortMalloc( size_t xWantedSize )
{
BlockLink_t *pxBlock, *pxPreviousBlock, *pxNewBlockLink;
void *pvReturn = NULL;

        vTaskSuspendAll();
        {
                /* If this is the first call to malloc then the heap will require
                initialisation to setup the list of free blocks. */
                if( pxEnd == NULL )
                {
                        prvHeapInit();
                }
                else
                {
                        mtCOVERAGE_TEST_MARKER();
                }

                /* Check the requested block size is not so large that the top bit is
                set.  The top bit of the block size member of the BlockLink_t structure
                is used to determine who owns the block - the application or the
                kernel, so it must be free. */
                if( ( xWantedSize & xBlockAllocatedBit ) == 0 )
                {
                        /* The wanted size is increased so it can contain a BlockLink_t
                        structure in addition to the requested amount of bytes. */
                        if( xWantedSize > 0 )
                        {
                                xWantedSize += xHeapStructSize;

                                /* Ensure that blocks are always aligned to the required number
                                of bytes. */
                                if( ( xWantedSize & portBYTE_ALIGNMENT_MASK ) != 0x00 )
                                {
                                        /* Byte alignment required. */
                                        xWantedSize += ( portBYTE_ALIGNMENT - ( xWantedSize & portBYTE_ALIGNMENT_MASK ) );
                                        configASSERT( ( xWantedSize & portBYTE_ALIGNMENT_MASK ) == 0 );
                                }
                                else
                                {
                                        mtCOVERAGE_TEST_MARKER();
                                }
                        }
                        else
                        {
                                mtCOVERAGE_TEST_MARKER();
                        }

                        if( ( xWantedSize > 0 ) && ( xWantedSize <= xFreeBytesRemaining ) )
                        {
                                /* Traverse the list from the start     (lowest address) block until
                                one     of adequate size is found. */
                                pxPreviousBlock = &xStart;
                                pxBlock = xStart.pxNextFreeBlock;
                                while( ( pxBlock->xBlockSize < xWantedSize ) && ( pxBlock->pxNextFreeBlock != NULL ) )
                                {
                                        pxPreviousBlock = pxBlock;
                                        pxBlock = pxBlock->pxNextFreeBlock;
                                }

                                /* If the end marker was reached then a block of adequate size
                                was     not found. */
                                if( pxBlock != pxEnd )
                                {
                                        /* Return the memory space pointed to - jumping over the
                                        BlockLink_t structure at its start. */
                                        pvReturn = ( void * ) ( ( ( uint8_t * ) pxPreviousBlock->pxNextFreeBlock ) + xHeapStructSize );

                                        /* This block is being returned for use so must be taken out
                                        of the list of free blocks. */
                                        pxPreviousBlock->pxNextFreeBlock = pxBlock->pxNextFreeBlock;

                                        /* If the block is larger than required it can be split into
                                        two. */
                                        if( ( pxBlock->xBlockSize - xWantedSize ) > heapMINIMUM_BLOCK_SIZE )
                                        {
                                                /* This block is to be split into two.  Create a new
                                                block following the number of bytes requested. The void
                                                cast is used to prevent byte alignment warnings from the
                                                compiler. */
                                                pxNewBlockLink = ( void * ) ( ( ( uint8_t * ) pxBlock ) + xWantedSize );
                                                configASSERT( ( ( ( size_t ) pxNewBlockLink ) & portBYTE_ALIGNMENT_MASK ) == 0 );

                                                /* Calculate the sizes of two blocks split from the
                                                single block. */
                                                pxNewBlockLink->xBlockSize = pxBlock->xBlockSize - xWantedSize;
                                                pxBlock->xBlockSize = xWantedSize;

                                                /* Insert the new block into the list of free blocks. */
                                                prvInsertBlockIntoFreeList( pxNewBlockLink );
                                        }
                                        else
                                        {
                                                mtCOVERAGE_TEST_MARKER();
                                        }

                                        xFreeBytesRemaining -= pxBlock->xBlockSize;

                                        if( xFreeBytesRemaining < xMinimumEverFreeBytesRemaining )
                                        {
                                                xMinimumEverFreeBytesRemaining = xFreeBytesRemaining;
                                        }
                                        else
                                        {
                                                mtCOVERAGE_TEST_MARKER();
                                        }

                                        /* The block is being returned - it is allocated and owned
                                        by the application and has no "next" block. */
                                        traceMALLOC(pvReturn, pxBlock->xBlockSize);
                                        pxBlock->xBlockSize |= xBlockAllocatedBit;
                                        pxBlock->pxNextFreeBlock = NULL;
                                }
                                else
                                {
                                        mtCOVERAGE_TEST_MARKER();
                                }
                        }
                        else
                        {
                                mtCOVERAGE_TEST_MARKER();
                        }
                }
                else
                {
                        mtCOVERAGE_TEST_MARKER();
                }
        }
        ( void ) xTaskResumeAll();

        #if( configUSE_MALLOC_FAILED_HOOK == 1 )
        {
                if( pvReturn == NULL )
                {
#if defined(__GNUC__)
#pragma GCC diagnostic push
#pragma GCC diagnostic ignored "-Wnested-externs"
#endif
                        extern void vApplicationMallocFailedHook( uint32_t, uint32_t );
#if defined(__GNUC__)
#pragma GCC diagnostic pop
#endif                  
                        vApplicationMallocFailedHook(xWantedSize, xFreeBytesRemaining);
                }
                else
                {
                        mtCOVERAGE_TEST_MARKER();
                }
        }
        #endif

        configASSERT( ( ( ( size_t ) pvReturn ) & ( size_t ) portBYTE_ALIGNMENT_MASK ) == 0 );
        return pvReturn;
}
/*-----------------------------------------------------------*/

void vPortFree( void *pv )
{
uint8_t *puc = ( uint8_t * ) pv;
BlockLink_t *pxLink;

        if( pv != NULL )
        {
                /* The memory being freed will have an BlockLink_t structure immediately
                before it. */
                puc -= xHeapStructSize;

                /* This casting is to keep the compiler from issuing warnings. */
                pxLink = ( void * ) puc;

                /* Check the block is actually allocated. */
                configASSERT( ( pxLink->xBlockSize & xBlockAllocatedBit ) != 0 );
                configASSERT( pxLink->pxNextFreeBlock == NULL );

                if( ( pxLink->xBlockSize & xBlockAllocatedBit ) != 0 )
                {
                        if( pxLink->pxNextFreeBlock == NULL )
                        {
                                /* The block is being returned to the heap - it is no longer
                                allocated. */
                                pxLink->xBlockSize &= ~xBlockAllocatedBit;

                                vTaskSuspendAll();
                                {
                                        /* Add this block to the list of free blocks. */
                                        xFreeBytesRemaining += pxLink->xBlockSize;
                                        traceFREE(pv, pxLink->xBlockSize);
                                        prvInsertBlockIntoFreeList( ( ( BlockLink_t * ) pxLink ) );
                                }
                                ( void ) xTaskResumeAll();
                        }
                        else
                        {
                                mtCOVERAGE_TEST_MARKER();
                        }
                }
                else
                {
                        mtCOVERAGE_TEST_MARKER();
                }
        }
}
/*-----------------------------------------------------------*/

size_t xPortGetFreeHeapSize( void )
{
        return xFreeBytesRemaining;
}
/*-----------------------------------------------------------*/

size_t xPortGetMinimumEverFreeHeapSize( void )
{
        return xMinimumEverFreeBytesRemaining;
}
/*-----------------------------------------------------------*/

void vPortInitialiseBlocks( void )
{
        /* This just exists to keep the linker quiet. */
}
/*-----------------------------------------------------------*/

static void prvHeapInit( void )
{
BlockLink_t *pxFirstFreeBlock;
uint8_t *pucAlignedHeap;
size_t uxAddress;
size_t xTotalHeapSize = configTOTAL_HEAP_SIZE;

        /* Ensure the heap starts on a correctly aligned boundary. */
        uxAddress = ( size_t ) ucHeap;

        if( ( uxAddress & portBYTE_ALIGNMENT_MASK ) != 0 )
        {
                uxAddress += ( portBYTE_ALIGNMENT - 1 );
                uxAddress &= ~( ( size_t ) portBYTE_ALIGNMENT_MASK );
                xTotalHeapSize -= uxAddress - ( size_t ) ucHeap;
        }

        pucAlignedHeap = ( uint8_t * ) uxAddress;

        /* xStart is used to hold a pointer to the first item in the list of free
        blocks.  The void cast is used to prevent compiler warnings. */
        xStart.pxNextFreeBlock = ( void * ) pucAlignedHeap;
        xStart.xBlockSize = ( size_t ) 0;

        /* pxEnd is used to mark the end of the list of free blocks and is inserted
        at the end of the heap space. */
        uxAddress = ( ( size_t ) pucAlignedHeap ) + xTotalHeapSize;
        uxAddress -= xHeapStructSize;
        uxAddress &= ~( ( size_t ) portBYTE_ALIGNMENT_MASK );
        pxEnd = ( void * ) uxAddress;
        pxEnd->xBlockSize = 0;
        pxEnd->pxNextFreeBlock = NULL;

        /* To start with there is a single free block that is sized to take up the
        entire heap space, minus the space taken by pxEnd. */
        pxFirstFreeBlock = ( void * ) pucAlignedHeap;
        pxFirstFreeBlock->xBlockSize = uxAddress - ( size_t ) pxFirstFreeBlock;
        pxFirstFreeBlock->pxNextFreeBlock = pxEnd;

        /* Only one block exists - and it covers the entire usable heap space. */
        xMinimumEverFreeBytesRemaining = pxFirstFreeBlock->xBlockSize;
        xFreeBytesRemaining = pxFirstFreeBlock->xBlockSize;

        /* Work out the position of the top bit in a size_t variable. */
        xBlockAllocatedBit = ( ( size_t ) 1 ) << ( ( sizeof( size_t ) * heapBITS_PER_BYTE ) - 1 );
}
/*-----------------------------------------------------------*/

static void prvInsertBlockIntoFreeList( BlockLink_t *pxBlockToInsert )
{
BlockLink_t *pxIterator;
uint8_t *puc;

        /* Iterate through the list until a block is found that has a higher address
        than the block being inserted. */
        for( pxIterator = &xStart; pxIterator->pxNextFreeBlock < pxBlockToInsert; pxIterator = pxIterator->pxNextFreeBlock )
        {
                /* Nothing to do here, just iterate to the right position. */
        }

        /* Do the block being inserted, and the block it is being inserted after
        make a contiguous block of memory? */
        puc = ( uint8_t * ) pxIterator;
        if( ( puc + pxIterator->xBlockSize ) == ( uint8_t * ) pxBlockToInsert )
        {
                pxIterator->xBlockSize += pxBlockToInsert->xBlockSize;
                pxBlockToInsert = pxIterator;
        }
        else
        {
                mtCOVERAGE_TEST_MARKER();
        }

        /* Do the block being inserted, and the block it is being inserted before
        make a contiguous block of memory? */
        puc = ( uint8_t * ) pxBlockToInsert;
        if( ( puc + pxBlockToInsert->xBlockSize ) == ( uint8_t * ) pxIterator->pxNextFreeBlock )
        {
                if( pxIterator->pxNextFreeBlock != pxEnd )
                {
                        /* Form one big block from the two blocks. */
                        pxBlockToInsert->xBlockSize += pxIterator->pxNextFreeBlock->xBlockSize;
                        pxBlockToInsert->pxNextFreeBlock = pxIterator->pxNextFreeBlock->pxNextFreeBlock;
                }
                else
                {
                        pxBlockToInsert->pxNextFreeBlock = pxEnd;
                }
        }
        else
        {
                pxBlockToInsert->pxNextFreeBlock = pxIterator->pxNextFreeBlock;
        }

        /* If the block being inserted plugged a gab, so was merged with the block
        before and the block after, then it's pxNextFreeBlock pointer will have
        already been set, and should not be set here as that would make it point
        to itself. */
        if( pxIterator != pxBlockToInsert )
        {
                pxIterator->pxNextFreeBlock = pxBlockToInsert;
        }
        else
        {
                mtCOVERAGE_TEST_MARKER();
        }
}