FreeRTOS Heap Memory Management (4) - heap4源码分析
/* FreeRTOS Kernel V10.4.1 */
原文链接：https://www.cnblogs.com/yanpio/p/14821851.html
heap4的实现与heap2非常相似，不同之处在于heap4需要合并相邻的 free block。请参考 FreeRTOS Heap Memory Management (3) - heap2源码分析。
1 变量与结构定义
#include <stdlib.h>
#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
PRIVILEGED_DATA static uint8_t ucHeap[ configTOTAL_HEAP_SIZE ];
#endif /* configAPPLICATION_ALLOCATED_HEAP */
/*
* 与heap2不同的是， xBlockSize成员的最高bit 表示该block是否被分配。
* size_t 被定义为 long long类型，因此最高位不可能被置位，所以拿来做标志位不会带来安全问题。
*/
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;
/* 函数申明，heap2中此函数被定义成宏，而此处是被定义成函数 */
static void prvInsertBlockIntoFreeList( BlockLink_t * pxBlockToInsert ) PRIVILEGED_FUNCTION;
static void prvHeapInit( void ) PRIVILEGED_FUNCTION;
/*-----------------------------------------------------------*/
/* 与heap2实现一致，可以参考heap2源码解析 */
static const size_t xHeapStructSize = ( sizeof( BlockLink_t ) + ( ( size_t ) ( portBYTE_ALIGNMENT - 1 ) ) ) & ~( ( size_t ) portBYTE_ALIGNMENT_MASK );
//与heap2.c不同，此处的pxEnd是指针， xStart ,pxEnd 初始化后，值不再变化
PRIVILEGED_DATA static BlockLink_t xStart, * pxEnd = NULL;
/* Keeps track of the number of calls to allocate and free memory as well as the
* number of free bytes remaining, but says nothing about fragmentation. */
PRIVILEGED_DATA static size_t xFreeBytesRemaining = 0U;
PRIVILEGED_DATA static size_t xMinimumEverFreeBytesRemaining = 0U;
PRIVILEGED_DATA static size_t xNumberOfSuccessfulAllocations = 0;
PRIVILEGED_DATA static size_t xNumberOfSuccessfulFrees = 0;
/* size_t 类型（long long）的最高位，结构体中的xBlockSize成员的最高位存储标志，0 - 未分配， 1 - 已分配
* 此变量在初始化时被赋值（0b1000000000000000000000000)，然后当做常量使用。用于判断 xBlockSize 的最高位是否为0
*/
PRIVILEGED_DATA static size_t xBlockAllocatedBit = 0;
2 prvInsertBlockIntoFreeList()
/* 此函数主要功能是将free block 重新插入到 free block list ，与heap2中的实现有较大差别。
* 一是插入的位置不同，二是插入后需要合并前后碎片。*/
static void prvInsertBlockIntoFreeList( BlockLink_t * pxBlockToInsert ) /* PRIVILEGED_FUNCTION */
{
BlockLink_t * pxIterator;
uint8_t * puc;
/* 注意，此处搜索的是最相近的地址，而不是最相近的大小，这与heap2不同。
* heap2中需要将free block 按照 size 大小进行排序，所以需要找到size相近的节点。
* 而heap4需要合并地址相邻的碎片，所以需要找到地址最相近的节点。 */
for( pxIterator = &xStart; pxIterator->pxNextFreeBlock < pxBlockToInsert; pxIterator = pxIterator->pxNextFreeBlock )
{
/* Nothing to do here, just iterate to the right position. */
}
/* 判断迭代器指向的free block（在插入free block的前面）是否和插入的free block相邻，如果相邻，则合并 */
puc = ( uint8_t * ) pxIterator;
if( ( puc + pxIterator->xBlockSize ) == ( uint8_t * ) pxBlockToInsert )
{
pxIterator->xBlockSize += pxBlockToInsert->xBlockSize;
pxBlockToInsert = pxIterator;
}
else
{
mtCOVERAGE_TEST_MARKER();
}
/* 判断插入的free block (可能已经和前一个free block合并) 是否与后面的free block相邻，如果是，则合并 */
puc = ( uint8_t * ) pxBlockToInsert;
if( ( puc + pxBlockToInsert->xBlockSize ) == ( uint8_t * ) pxIterator->pxNextFreeBlock )
{
/* 如果pxIterator指向的不是pEnd，则进行合并，否则就直接指向pEnd，而不需要合并 */
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;
}
/* 如果前后都没有合并，则直接将节点插入即可 */
if( pxIterator != pxBlockToInsert )
{
pxIterator->pxNextFreeBlock = pxBlockToInsert;
}
else
{
mtCOVERAGE_TEST_MARKER();
}
}
3 prvHeapInit()
static void prvHeapInit( void ) /* PRIVILEGED_FUNCTION */
{
BlockLink_t * pxFirstFreeBlock;
uint8_t * pucAlignedHeap; //对齐后的空间地址
size_t uxAddress;
size_t xTotalHeapSize = configTOTAL_HEAP_SIZE;
/* 对齐ucHeap，思路见heap2 */
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;
}
/* 初始化头节点 xStart */
pucAlignedHeap = ( uint8_t * ) uxAddress;
xStart.pxNextFreeBlock = ( void * ) pucAlignedHeap;
xStart.xBlockSize = ( size_t ) 0;
/* pxEnd初始化的方式与heap2不同
* pxEnd是指针，并且指向的结构体插入在heap的最后面*/
uxAddress = ( ( size_t ) pucAlignedHeap ) + xTotalHeapSize;
uxAddress -= xHeapStructSize; /* 留出pxEnd指向的结构体需要占用的空间 */
uxAddress &= ~( ( size_t ) portBYTE_ALIGNMENT_MASK );/* 内存对齐 */
pxEnd = ( void * ) uxAddress;
pxEnd->xBlockSize = 0;
pxEnd->pxNextFreeBlock = NULL;
/* 创建第一个节点，此时整个heap都被这个节点指向的block占据 */
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;
/* 初始化数值，即将size_t类型的数值最高位置1。初始化后，此值只用于判断，值不再变化 */
xBlockAllocatedBit = ( ( size_t ) 1 ) << ( ( sizeof( size_t ) * heapBITS_PER_BYTE ) - 1 );
}
4 pvPortMalloc()
void * pvPortMalloc( size_t xWantedSize )
{
BlockLink_t * pxBlock, * pxPreviousBlock, * pxNewBlockLink;
void * pvReturn = NULL;
vTaskSuspendAll();
{
/* 如果pxEnd值等于初始值（未初始化），则进行初始化 */
if( pxEnd == NULL )
{
prvHeapInit();
}
else
{
mtCOVERAGE_TEST_MARKER();
}
/* 如果 xWantedSize 的最高位为1 ，则在赋值时会覆盖xBlockSize的最高位（标志位，标志该block是否已分配）
* 因此必须先检查。正常情况下，xWantedSize 的最高位不可能为1 ，因为size_t (long long)的最高位如果是1，则这个数是负数 */
if( ( xWantedSize & xBlockAllocatedBit ) == 0 )
{
/* xWantedSize + xHeapStructSize， 然后进行内存对齐 */
if( xWantedSize > 0 )
{
xWantedSize += xHeapStructSize;
if( ( xWantedSize & portBYTE_ALIGNMENT_MASK ) != 0x00 )
{
xWantedSize += ( portBYTE_ALIGNMENT - ( xWantedSize & portBYTE_ALIGNMENT_MASK ) );
//#define configASSERT( x ) if( x == 0 ) { taskDISABLE_INTERRUPTS(); for(;;); }
configASSERT( ( xWantedSize & portBYTE_ALIGNMENT_MASK ) == 0 );
}
else
{
mtCOVERAGE_TEST_MARKER();
}
}
else
{
mtCOVERAGE_TEST_MARKER();
}
/* 分配内存 */
if( ( xWantedSize > 0 ) && ( xWantedSize <= xFreeBytesRemaining ) )
{
/* heap4的free block是按照地址高低进行排序的，从低地址开始迭代，直到找到一个xBlockSize满足要求的free block */
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 )
{
//在内存上偏移首部的结构体长度
pvReturn = ( void * ) ( ( ( uint8_t * ) pxPreviousBlock->pxNextFreeBlock ) + xHeapStructSize );
//将分配出去的内存从链表节点删除
pxPreviousBlock->pxNextFreeBlock = pxBlock->pxNextFreeBlock;
/* 如果该内存的空间大于所需内存，则将多余内存回收到空闲列表中 */
if( ( pxBlock->xBlockSize - xWantedSize ) > heapMINIMUM_BLOCK_SIZE )
{
pxNewBlockLink = ( void * ) ( ( ( uint8_t * ) pxBlock ) + xWantedSize );
configASSERT( ( ( ( size_t ) pxNewBlockLink ) & portBYTE_ALIGNMENT_MASK ) == 0 );
/* 计算分割后的两个block的xBlockSize值 */
pxNewBlockLink->xBlockSize = pxBlock->xBlockSize - xWantedSize;
pxBlock->xBlockSize = xWantedSize;
/* 回收多余空间 */
prvInsertBlockIntoFreeList( pxNewBlockLink );
}
else
{
mtCOVERAGE_TEST_MARKER();
}
xFreeBytesRemaining -= pxBlock->xBlockSize;
/* 更新最小剩余空间 */
if( xFreeBytesRemaining < xMinimumEverFreeBytesRemaining )
{
xMinimumEverFreeBytesRemaining = xFreeBytesRemaining;
}
else
{
mtCOVERAGE_TEST_MARKER();
}
/* 置标志位，已经分配出去的block 指向null. */
pxBlock->xBlockSize |= xBlockAllocatedBit;
pxBlock->pxNextFreeBlock = NULL;
xNumberOfSuccessfulAllocations++;
}
else
{
mtCOVERAGE_TEST_MARKER();
}
}
else
{
mtCOVERAGE_TEST_MARKER();
}
}
else
{
mtCOVERAGE_TEST_MARKER();
}
traceMALLOC( pvReturn, xWantedSize );
}
( void ) xTaskResumeAll();
/* 如果使用钩子函数，则在分配失败后进行调用 */
#if ( configUSE_MALLOC_FAILED_HOOK == 1 )
{
if( pvReturn == NULL )
{
extern void vApplicationMallocFailedHook( void );
vApplicationMallocFailedHook();
}
else
{
mtCOVERAGE_TEST_MARKER();
}
}
#endif /* if ( configUSE_MALLOC_FAILED_HOOK == 1 ) */
configASSERT( ( ( ( size_t ) pvReturn ) & ( size_t ) portBYTE_ALIGNMENT_MASK ) == 0 );
return pvReturn;
}
5 vPortFree()
void vPortFree( void * pv )
{
uint8_t * puc = ( uint8_t * ) pv;
BlockLink_t * pxLink;
if( pv != NULL )
{
/* 将结构体变量的空间也释放掉 */
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 );
/* 释放内存，并插入到空闲列表中 */
if( ( pxLink->xBlockSize & xBlockAllocatedBit ) != 0 )
{
if( pxLink->pxNextFreeBlock == NULL )
{
/* 清除标志位 */
pxLink->xBlockSize &= ~xBlockAllocatedBit;
vTaskSuspendAll();
{
/* 将释放掉的空间插入到空闲列表中. */
xFreeBytesRemaining += pxLink->xBlockSize;
traceFREE( pv, pxLink->xBlockSize );
prvInsertBlockIntoFreeList( ( ( BlockLink_t * ) pxLink ) );
xNumberOfSuccessfulFrees++;
}
( void ) xTaskResumeAll();
}
else
{
mtCOVERAGE_TEST_MARKER();
}
}
else
{
mtCOVERAGE_TEST_MARKER();
}
}
}
6 vPortGetHeapStats()
/* 结构体定义了关于heap状态的一些变量 */
typedef struct xHeapStats
{
/* The total heap size available - this is the sum of all the free blocks, not the largest block that can be allocated.*/
size_t xAvailableHeapSpaceInBytes;
/* The maximum size, in bytes, of all the free blocks within the heap at the time vPortGetHeapStats() is called. */
size_t xSizeOfLargestFreeBlockInBytes;
/* The minimum size, in bytes, of all the free blocks within the heap at the time vPortGetHeapStats() is called. */
size_t xSizeOfSmallestFreeBlockInBytes;
/* The number of free memory blocks within the heap at the time vPortGetHeapStats() is called. */
size_t xNumberOfFreeBlocks;
/* The minimum amount of total free memory (sum of all free blocks) there has been in the heap since the system booted.*/
size_t xMinimumEverFreeBytesRemaining;
/* The number of calls to pvPortMalloc() that have returned a valid memory block. */
size_t xNumberOfSuccessfulAllocations;
/* The number of calls to vPortFree() that has successfully freed a block of memory. */
size_t xNumberOfSuccessfulFrees;
} HeapStats_t;
/* 获取heap的一些信息 */
void vPortGetHeapStats( HeapStats_t * pxHeapStats )
{
BlockLink_t * pxBlock;
/* portMAX_DELAY used as a portable way of getting the maximum value. */
size_t xBlocks = 0, xMaxSize = 0, xMinSize = portMAX_DELAY;
vTaskSuspendAll();
{
pxBlock = xStart.pxNextFreeBlock;
/* 搜索最大和最小的block. */
if( pxBlock != NULL )
{
do
{
/* Increment the number of blocks and record the largest block seen so far. */
xBlocks++;
if( pxBlock->xBlockSize > xMaxSize )
{
xMaxSize = pxBlock->xBlockSize;
}
if( pxBlock->xBlockSize < xMinSize )
{
xMinSize = pxBlock->xBlockSize;
}
pxBlock = pxBlock->pxNextFreeBlock;
} while( pxBlock != pxEnd );
}
}
( void ) xTaskResumeAll();
/* 填充数值 */
pxHeapStats->xSizeOfLargestFreeBlockInBytes = xMaxSize;
pxHeapStats->xSizeOfSmallestFreeBlockInBytes = xMinSize;
pxHeapStats->xNumberOfFreeBlocks = xBlocks;
taskENTER_CRITICAL();
{
pxHeapStats->xAvailableHeapSpaceInBytes = xFreeBytesRemaining;
pxHeapStats->xNumberOfSuccessfulAllocations = xNumberOfSuccessfulAllocations;
pxHeapStats->xNumberOfSuccessfulFrees = xNumberOfSuccessfulFrees;
pxHeapStats->xMinimumEverFreeBytesRemaining = xMinimumEverFreeBytesRemaining;
}
taskEXIT_CRITICAL();
}
7 其他函数
size_t xPortGetFreeHeapSize( void )
{
return xFreeBytesRemaining;
}
/*-----------------------------------------------------------*/
size_t xPortGetMinimumEverFreeHeapSize( void )
{
return xMinimumEverFreeBytesRemaining;
}
/*-----------------------------------------------------------*/
void vPortInitialiseBlocks( void )
{
/* This just exists to keep the linker quiet. */
}
/*-----------------------------------------------------------*/
