在rtems中，可以通过region来分配内存，这样分配的内存可以独立于malloc申请的内存，从而实现内存区域的管理。本文基于此分享如何使用内存区域
一、作用
内存区域的作用是单独的内存区域，这个区域是固定的起始地址，大小和属性。使用内存区域的情况下，可以避免内存回收，内存规整等操作带来的性能消耗，同样的，也可以为多个任务创建不同的内存区域。
当然，在rtems中，如果分配内存区域的时候内存不足，也可以将任务进入等待队列，直到内存释放后有可用内存时。
二、代码实现
内存区域的代码如下
rtems_status_code rtems_region_create( rtems_name name, void *starting_address, uintptr_t length, uintptr_t page_size, rtems_attribute attribute_set, rtems_id *id ) { rtems_status_code return_status; Region_Control *the_region; if ( !rtems_is_name_valid( name ) ) { return RTEMS_INVALID_NAME; } if ( id == NULL ) { return RTEMS_INVALID_ADDRESS; } if ( starting_address == NULL ) { return RTEMS_INVALID_ADDRESS; } the_region = _Region_Allocate(); if ( !the_region ) return_status = RTEMS_TOO_MANY; else { _Thread_queue_Object_initialize( &the_region->Wait_queue ); if ( _Attributes_Is_priority( attribute_set ) ) { the_region->wait_operations = &_Thread_queue_Operations_priority; } else { the_region->wait_operations = &_Thread_queue_Operations_FIFO; } the_region->maximum_segment_size = _Heap_Initialize( &the_region->Memory, starting_address, length, page_size ); if ( !the_region->maximum_segment_size ) { _Region_Free( the_region ); return_status = RTEMS_INVALID_SIZE; } else { the_region->attribute_set = attribute_set; *id = _Objects_Open_u32( &_Region_Information, &the_region->Object, name ); return_status = RTEMS_SUCCESSFUL; } } _Objects_Allocator_unlock(); return return_status; }
2.1 解析形参
name：内存区域名称
starting_address：需要申请的内存地址
length：内存区域大小
page_size： 设置内存区域的页大小
attribute_set： 设置内存的调度属性
id： 内存区域id
2.2 内存管理线程
rtems提供两种线程方式：一个是fifo，也就是先进先出调度，另一个是priority，也就是基于优先级的调度，分别如下：
const Thread_queue_Operations _Thread_queue_Operations_FIFO = { .priority_actions = _Thread_queue_Do_nothing_priority_actions, .enqueue = _Thread_queue_FIFO_enqueue, .extract = _Thread_queue_FIFO_extract, .surrender = _Thread_queue_FIFO_surrender, .first = _Thread_queue_FIFO_first }; const Thread_queue_Operations _Thread_queue_Operations_priority = { .priority_actions = _Thread_queue_Priority_priority_actions, .enqueue = _Thread_queue_Priority_enqueue, .extract = _Thread_queue_Priority_extract, .surrender = _Thread_queue_Priority_surrender, .first = _Thread_queue_Priority_first };
这个初始化的线程，会在内存不足的时候阻塞。
2.3 申请堆
通过_Heap_Initialize直接申请堆作为内存区域的Memory成员。地址指向starting_address
2.4 设置属性和申请id
对于这块内存，可以设置region结构体的属性字段，并通过_Objects_Open_u32申请内存区域id。region结构体如下
typedef struct { Objects_Control Object; Thread_queue_Control Wait_queue; /* waiting threads */ const Thread_queue_Operations *wait_operations; uintptr_t maximum_segment_size; /* in bytes */ rtems_attribute attribute_set; Heap_Control Memory; } Region_Control;
三、测试分配内存
测试分配内存区域非常简单，我们可以直接通过rtems_region_create分配即可，如下：
static const rtems_name name = rtems_build_name('K', 'Y', 'L', 'I'); #define CONFIGURE_MAXIMUM_REGIONS 1 static void test_region_create(void) { rtems_status_code sc; rtems_id id; void *seg_addr1; void *seg_addr2; sc = rtems_region_create( name, 0x4000000, 640, 16, RTEMS_DEFAULT_ATTRIBUTES, &id ); printf( "sc=%d\n", sc); sc = rtems_region_get_segment( id, 32, RTEMS_DEFAULT_OPTIONS, RTEMS_NO_TIMEOUT, &seg_addr1 ); printf( "sc=%d seg_addr=%p\n", sc, seg_addr1); sc = rtems_region_get_segment( id, 32, RTEMS_DEFAULT_OPTIONS, RTEMS_NO_TIMEOUT, &seg_addr2 ); printf( "sc=%d seg_addr=%p\n", sc, seg_addr2); sc = rtems_region_return_segment( id, seg_addr1); printf( "sc=%d\n", sc); sc = rtems_region_return_segment( id, seg_addr2); printf( "sc=%d\n", sc); }
3.1 region个数
默认情况下，需要通过一个宏设置内存区域个数CONFIGURE_MAXIMUM_REGIONS，这里定义多少就代表系统最多可以申请多少region
3.2 最小申请大小
内存区域最小分配为64字节，准确来说是大于等于52字节，这样内存区域才能正常工作。否则rtems_region_create返回无效
3.3 获取内存
通过rtems_region_get_segment可以获取region的段，这样就能直接使用region
3.4 释放内存到内存
通过rtems_region_get_segment可以释放region的段，这样下一个程序可以重新分配
3.5 测试程序内存布局
内存布局如下
(gdb) x/14g 0x4000000 0x4000000: 0x0000000004000280 0x0000000000000031 0x4000010: 0x0000000004000060 0x0000000000105d68 0x4000020: 0x0000000000000000 0x0000000000000000 0x4000030: 0x0000000000000030 0x0000000000000030 0x4000040: 0x0000000000105d68 0x0000000000105d68 0x4000050: 0x0000000000000000 0x0000000000000000 0x4000060: 0x0000000000000000 0x0000000000000211
从heap block结构体可以看到，内存分配一切正常
四、总结
通过上述的实验，可以清楚的了解到rtems的region的分配和原理。这里分配固定地址上的内存块，供程序使用
rtems不仅支持malloc，还支持region分配，这两个都是基于heap来分配的，而partition的内存分配是直接通过链表管理的内存池，他不会记录block信息，本文介绍partition分配内存
一、测试代码
复用测试region的代码，稍作修改可以直接测试partition，如下
#define CONFIGURE_MAXIMUM_PARTITIONS 1 static void test_partition_create(void) { rtems_status_code sc; rtems_id id; void *partition_buf1; void *partition_buf2; sc = rtems_partition_create( name, (void* )0x4000000, 128, 32, RTEMS_DEFAULT_ATTRIBUTES, &id ); printf( "sc=%d \n", sc); sc = rtems_partition_get_buffer( id, &partition_buf1); printf( "sc=%d buf1=%p\n", sc, partition_buf1); sc = rtems_partition_get_buffer( id, &partition_buf2); printf( "sc=%d buf2=%p\n", sc, partition_buf2); sc = rtems_partition_return_buffer(id, partition_buf1); printf( "sc=%d \n", sc); sc = rtems_partition_return_buffer(id, partition_buf2); printf( "sc=%d \n", sc); return ; }
二、测试运行
直接测试效果如下：
(gdb) x/14xg 0x4000000 0x4000000: 0x0000000004000020 0x00000000001056d0 0x4000010: 0x0000000000000000 0x0000000000000000 0x4000020: 0x0000000004000040 0x00000000001056d0 0x4000030: 0x0000000000000000 0x0000000000000000 0x4000040: 0x0000000004000060 0x00000000001056d0 0x4000050: 0x0000000000000000 0x0000000000000000 0x4000060: 0x00000000001056d8 0x0000000004000040
可以发现，我申请了128内存，按照32字节划分，那么每块都是0x20大小，如果起始地址是0x4000000，则划分为如下
0x4000000/0x4000020/0x4000040/0x4000060
值得注意的是partition分配的内存，不会带block结构体，也就少了16字节的冗余，这种情况下，也不会参与内存的回收，规整，相当于蛋糕自己随便分，整体效率是最高的。
如果留意这些分区的内存的话，可以发现管理这些内存使用的是16字节的链表。接下来分析代码
三、代码解析
3.1 create
创建分区代码如下
rtems_status_code rtems_partition_create( rtems_name name, void *starting_address, uintptr_t length, size_t buffer_size, rtems_attribute attribute_set, rtems_id *id ) { Partition_Control *the_partition; if ( !rtems_is_name_valid( name ) ) { return RTEMS_INVALID_NAME; } if ( id == NULL ) { return RTEMS_INVALID_ADDRESS; } if ( starting_address == NULL ) { return RTEMS_INVALID_ADDRESS; } if ( length == 0 ) { return RTEMS_INVALID_SIZE; } if ( buffer_size == 0 ) { return RTEMS_INVALID_SIZE; } if ( length < buffer_size ) { return RTEMS_INVALID_SIZE; } /* * Ensure that the buffer size is an integral multiple of the pointer size so * that each buffer begin meets the chain node alignment. */ if ( buffer_size % CPU_SIZEOF_POINTER != 0 ) { return RTEMS_INVALID_SIZE; } if ( buffer_size < sizeof( Chain_Node ) ) return RTEMS_INVALID_SIZE; /* * Ensure that the buffer area starting address is aligned on a pointer * boundary so that each buffer begin meets the chain node alignment. */ if ( (uintptr_t) starting_address % CPU_SIZEOF_POINTER != 0 ) { return RTEMS_INVALID_ADDRESS; } #if defined(RTEMS_MULTIPROCESSING) if ( !_System_state_Is_multiprocessing ) { attribute_set = _Attributes_Clear( attribute_set, RTEMS_GLOBAL ); } #endif the_partition = _Partition_Allocate(); if ( !the_partition ) { _Objects_Allocator_unlock(); return RTEMS_TOO_MANY; } #if defined(RTEMS_MULTIPROCESSING) if ( _Attributes_Is_global( attribute_set ) && !( _Objects_MP_Allocate_and_open( &_Partition_Information, name, the_partition->Object.id, false ) ) ) { _Objects_Free( &_Partition_Information, &the_partition->Object ); _Objects_Allocator_unlock(); return RTEMS_TOO_MANY; } #endif _Partition_Initialize( the_partition, starting_address, length, buffer_size, attribute_set ); *id = _Objects_Open_u32( &_Partition_Information, &the_partition->Object, name ); #if defined(RTEMS_MULTIPROCESSING) if ( _Attributes_Is_global( attribute_set ) ) _Partition_MP_Send_process_packet( PARTITION_MP_ANNOUNCE_CREATE, the_partition->Object.id, name, 0 /* Not used */ ); #endif _Objects_Allocator_unlock(); return RTEMS_SUCCESSFUL; }
这里的重点是
_Partition_Initialize( the_partition, starting_address, length, buffer_size, attribute_set );
可以查到_Partition_Initialize调用的_Chain_Initialize，我们查看_Chain_Initialize的实现如下
void _Chain_Initialize( Chain_Control *the_chain, void *starting_address, size_t number_nodes, size_t node_size ) { size_t count = number_nodes; Chain_Node *head = _Chain_Head( the_chain ); Chain_Node *tail = _Chain_Tail( the_chain ); Chain_Node *current = head; Chain_Node *next = starting_address; _Assert( node_size >= sizeof( *next ) ); head->previous = NULL; while ( count-- ) { current->next = next; next->previous = current; current = next; next = (Chain_Node *) _Addresses_Add_offset( (void *) next, node_size ); } current->next = tail; tail->previous = current; }
可以发现， 这里定义了一个双链表，其中count就是分区的数量，根据分区的数量直接填充链表的成员，链表非常简单，如下：
typedef struct Chain_Node { /** This points to the node after this one on this chain. */ struct Chain_Node *next; /** This points to the node immediate prior to this one on this chain. */ struct Chain_Node *previous; } Chain_Node;
可以发现，和测试运行中的内存布局完全一致。
3.2 get buffer
rtems_partition_get_buffer函数的实现如下：
rtems_status_code rtems_partition_get_buffer( rtems_id id, void **buffer ) { Partition_Control *the_partition; ISR_lock_Context lock_context; void *the_buffer; if ( buffer == NULL ) { return RTEMS_INVALID_ADDRESS; } the_partition = _Partition_Get( id, &lock_context ); if ( the_partition == NULL ) { #if defined(RTEMS_MULTIPROCESSING) return _Partition_MP_Get_buffer( id, buffer ); #else return RTEMS_INVALID_ID; #endif } _Partition_Acquire_critical( the_partition, &lock_context ); the_buffer = _Partition_Allocate_buffer( the_partition ); if ( the_buffer == NULL ) { _Partition_Release( the_partition, &lock_context ); return RTEMS_UNSATISFIED; } the_partition->number_of_used_blocks += 1; _Partition_Release( the_partition, &lock_context ); *buffer = the_buffer; return RTEMS_SUCCESSFUL; }
代码熟悉了就发现非常简单，我们关注_Partition_Allocate_buffer，它调用_Chain_Get_unprotected，然后调用_Chain_Get_first_unprotected
_Chain_Get_first_unprotected的实现如下
static inline Chain_Node *_Chain_Get_first_unprotected( Chain_Control *the_chain ) { Chain_Node *head; Chain_Node *old_first; Chain_Node *new_first; _Assert( !_Chain_Is_empty( the_chain ) ); head = _Chain_Head( the_chain ); old_first = head->next; new_first = old_first->next; head->next = new_first; new_first->previous = head; #if defined(RTEMS_DEBUG) _Chain_Set_off_chain( old_first ); #endif return old_first; }
可以发现，这里get buffer的操作就是取出head，然后通过head拿到next返回，并且将head->next->next返回给head→next，相当于list的del head操作
3.3 return buffer
rtems_partition_return_buffer的实现如下：
rtems_status_code rtems_partition_return_buffer( rtems_id id, void *buffer ) { Partition_Control *the_partition; ISR_lock_Context lock_context; the_partition = _Partition_Get( id, &lock_context ); if ( the_partition == NULL ) { #if defined(RTEMS_MULTIPROCESSING) return _Partition_MP_Return_buffer( id, buffer ); #else return RTEMS_INVALID_ID; #endif } _Partition_Acquire_critical( the_partition, &lock_context ); if ( !_Partition_Is_address_a_buffer_begin( the_partition, buffer ) ) { _Partition_Release( the_partition, &lock_context ); return RTEMS_INVALID_ADDRESS; } _Partition_Free_buffer( the_partition, buffer ); the_partition->number_of_used_blocks -= 1; _Partition_Release( the_partition, &lock_context ); return RTEMS_SUCCESSFUL; }
同样的，我们关注_Partition_Free_buffer，从而关注_Chain_Append_unprotected，其实现如下
static inline void _Chain_Append_unprotected( Chain_Control *the_chain, Chain_Node *the_node ) { Chain_Node *tail; Chain_Node *old_last; _Assert( _Chain_Is_node_off_chain( the_node ) ); tail = _Chain_Tail( the_chain ); old_last = tail->previous; the_node->next = tail; tail->previous = the_node; old_last->next = the_node; the_node->previous = old_last; }
这里就是对双链表做了尾插，list add tail。
四、总结
至此，关于rtems partition 内存的操作介绍完毕了。可以发现，如果不需要碎片管理，则partition的内存分配相当于内存池，简单高效。
在bootcard中有流程是heap的初始化，为了更详细的了解内存初始化，这里以_Heap_Initialize为入口，详细了解具体做了什么
一、RTEMS默认初始化哪些堆
我们之前分析流程的时候，可以知道RTEMS初始化了多个堆，主要如下
_Workspace_Handler_initialization 会初始化_Heap_Initialize _Malloc_Initialize 会初始化 _Heap_Initialize add_area的cache_coherent_heap会初始化_Heap_Initialize
总共三个heap区，本文以malloc为例关注_Heap_Initialize 的初始化
二、代码解析
uintptr_t _Heap_Initialize( Heap_Control *heap, void *heap_area_begin_ptr, // 起始地址 uintptr_t heap_area_size, // 大小 uintptr_t page_size ) { Heap_Statistics *const stats = &heap->stats; uintptr_t const heap_area_begin = (uintptr_t) heap_area_begin_ptr; uintptr_t const heap_area_end = heap_area_begin + heap_area_size; uintptr_t first_block_begin = 0; uintptr_t first_block_size = 0; uintptr_t last_block_begin = 0; uintptr_t min_block_size = 0; bool area_ok = false; Heap_Block *first_block = NULL; Heap_Block *last_block = NULL; // 如果page_size 没有设置，则设置为cpu对齐大小，否则按照设置大小向cpu对齐 if ( page_size == 0 ) { page_size = CPU_ALIGNMENT; } else { page_size = _Heap_Align_up( page_size, CPU_ALIGNMENT ); if ( page_size < CPU_ALIGNMENT ) { /* Integer overflow */ return 0; } } // 计算最小的块大小 min_block_size = _Heap_Min_block_size( page_size ); // 获取第一个块和最后一个块的地址 area_ok = _Heap_Get_first_and_last_block( heap_area_begin, heap_area_size, page_size, min_block_size, &first_block, &last_block ); if ( !area_ok ) { return 0; } memset(heap, 0, sizeof(*heap)); #ifdef HEAP_PROTECTION heap->Protection.block_initialize = _Heap_Protection_block_initialize_default; heap->Protection.block_check = _Heap_Protection_block_check_default; heap->Protection.block_error = _Heap_Protection_block_error_default; #endif // 计算第一个块的大小，拿最后一个块的开始减去第一个块的开始 first_block_begin = (uintptr_t) first_block; last_block_begin = (uintptr_t) last_block; first_block_size = last_block_begin - first_block_begin; // 设置第一个块，结合block的结构体，将prev_size设置为堆的末尾 // 将第一个块的next设置为空闲链表的尾，prev设置为空闲链表的头，这里相当于初始化空闲链表 /* First block */ first_block->prev_size = heap_area_end; first_block->size_and_flag = first_block_size | HEAP_PREV_BLOCK_USED; first_block->next = _Heap_Free_list_tail( heap ); first_block->prev = _Heap_Free_list_head( heap ); _Heap_Protection_block_initialize( heap, first_block ); // 报错堆的信息，如页大小，最小块大小，堆范围，第一个块地址，最后一个块地址 // 设置空闲链表的第一个元素是first_block /* Heap control */ heap->page_size = page_size; heap->min_block_size = min_block_size; heap->area_begin = heap_area_begin; heap->area_end = heap_area_end; heap->first_block = first_block; heap->last_block = last_block; _Heap_Free_list_head( heap )->next = first_block; _Heap_Free_list_tail( heap )->prev = first_block; // 将最后一个blokc的prev_size设置为第一个block的size /* Last block */ last_block->prev_size = first_block_size; last_block->size_and_flag = 0; _Heap_Set_last_block_size( heap ); _Heap_Protection_block_initialize( heap, last_block ); // 统计信息 总大小，空闲大小，块数 /* Statistics */ stats->size = first_block_size; stats->free_size = first_block_size; stats->min_free_size = first_block_size; stats->free_blocks = 1; stats->max_free_blocks = 1; _Heap_Protection_set_delayed_free_fraction( heap, 2 ); _HAssert( _Heap_Is_aligned( heap->page_size, CPU_ALIGNMENT ) ); _HAssert( _Heap_Is_aligned( heap->min_block_size, page_size ) ); _HAssert( _Heap_Is_aligned( _Heap_Alloc_area_of_block( first_block ), page_size ) ); _HAssert( _Heap_Is_aligned( _Heap_Alloc_area_of_block( last_block ), page_size ) ); // 返回第一个块的大小 return first_block_size; }
代码中有注释，我们可以知道，对于heap初始化来说，其主要是构造了Heap_Control *heap结构体，然后计算Heap_Block的大小来分配每个block，并为每个block来构造block信息，最后设置heap的统计信息。
三、确认构造信息
根据gdb我们可以观察heap构造情况，首先查看heap control结构体,结构体定义如下：
struct Heap_Control { Heap_Block free_list; uintptr_t page_size; uintptr_t min_block_size; uintptr_t area_begin; uintptr_t area_end; Heap_Block *first_block; Heap_Block *last_block; Heap_Statistics stats; #ifdef HEAP_PROTECTION Heap_Protection Protection; #endif };
实际信息如下
(gdb) p _Malloc_Heap $1 = {free_list = {prev_size = 0, size_and_flag = 0, next = 0x0, prev = 0x0}, page_size = 0, min_block_size = 0, area_begin = 0, area_end = 0, first_block = 0x0, last_block = 0x0, stats = {lifetime_allocated = 0, lifetime_freed = 0, size = 0, free_size = 0, min_free_size = 0, free_blocks = 0, max_free_blocks = 0, used_blocks = 0, max_search = 0, searches = 0, allocs = 0, failed_allocs = 0, frees = 0, resizes = 0}}(gdb) p _Malloc_Heap $2 = {free_list = {prev_size = 0, size_and_flag = 0, next = 0x1342a0, prev = 0x1342a0}, page_size = 16, min_block_size = 32, area_begin = 1262239, area_end = 1072431104, first_block = 0x1342a0, last_block = 0x3febfff0, stats = { lifetime_allocated = 0, lifetime_freed = 0, size = 1071168848, free_size = 1071168848, min_free_size = 1071168848, free_blocks = 1, max_free_blocks = 1, used_blocks = 0, max_search = 0, searches = 0, allocs = 0, failed_allocs = 0, frees = 0, resizes = 0}}
heap block结构体如下
struct Heap_Block { uintptr_t prev_size; uintptr_t size_and_flag; Heap_Block *next; Heap_Block *prev; };
实际信息如下
(gdb) p *(Heap_Block *)0x1342a0 $5 = {prev_size = 1072431104, size_and_flag = 1071168849, next = 0x102c90 <_Malloc_Heap>, prev = 0x102c90 <_Malloc_Heap>}(gdb) p *(Heap_Block *)0x3febfff0 $6 = {prev_size = 1071168848, size_and_flag = 18446744072638382768, next = 0x0, prev = 0x0}
heap statistics结构体如下
typedef struct { /** * @brief Lifetime number of bytes allocated from this heap. * * This value is an integral multiple of the page size. */ uint64_t lifetime_allocated; /** * @brief Lifetime number of bytes freed to this heap. * * This value is an integral multiple of the page size. */ uint64_t lifetime_freed; /** * @brief Size of the allocatable area in bytes. * * This value is an integral multiple of the page size. */ uintptr_t size; /** * @brief Current free size in bytes. * * This value is an integral multiple of the page size. */ uintptr_t free_size; /** * @brief Minimum free size ever in bytes. * * This value is an integral multiple of the page size. */ uintptr_t min_free_size; /** * @brief Current number of free blocks. */ uint32_t free_blocks; /** * @brief Maximum number of free blocks ever. */ uint32_t max_free_blocks; /** * @brief Current number of used blocks. */ uint32_t used_blocks; /** * @brief Maximum number of blocks searched ever. */ uint32_t max_search; /** * @brief Total number of searches. */ uint32_t searches; /** * @brief Total number of successful allocations. */ uint32_t allocs; /** * @brief Total number of failed allocations. */ uint32_t failed_allocs; /** * @brief Total number of successful frees. */ uint32_t frees; /** * @brief Total number of successful resizes. */ uint32_t resizes; } Heap_Statistics;
实际信息在heap结构体已经打印，这里摘出来如下
(gdb) p _Malloc_Heap->stats $10 = {lifetime_allocated = 0, lifetime_freed = 0, size = 0, free_size = 0, min_free_size = 0, free_blocks = 0, max_free_blocks = 0, used_blocks = 0, max_search = 0, searches = 0, allocs = 0, failed_allocs = 0, frees = 0, resizes = 0}(gdb) p _Malloc_Heap->stats $11 = {lifetime_allocated = 0, lifetime_freed = 0, size = 1071168848, free_size = 1071168848, min_free_size = 1071168848, free_blocks = 1, max_free_blocks = 1, used_blocks = 0, max_search = 0, searches = 0, allocs = 0, failed_allocs = 0, frees = 0, resizes = 0}
四、总结
至此，我们清楚的知道了RTEMS系统的堆的初始化方式。后续调试堆的时候，这些结构体对我们非常有用
rtems支持阻塞任务调度，这个名字听起来有点奇怪，按照通俗的理解，就是当任务遇到IO事件或等待事件时，可以将任务设置为阻塞状态，然后将其从就绪队列移除
一、测试程序
对于阻塞任务调度，我们可以两种方式测试
- 主动等待睡眠
- 线程任务挂起
对于上面两种程序，主要是两个函数：rtems_task_suspend/rtems_task_wake_after
为了测试阻塞任务调度，本文基于rtems_task_wake_after来测试，rtems_task_suspend方法一致，就不演示了。
测试rtems_task_wake_after，可以借鉴原有的验证程序，我们可以在Process_asr函数中，将rtems_task_wake_after( RTEMS_YIELD_PROCESSOR );设置为status = rtems_task_wake_after( rtems_clock_get_ticks_per_second() );
这里tick是100为1s。修改了0为100后，rtems_task_wake_after会主动block线程，如下代码：
rtems_status_code rtems_task_wake_after( rtems_interval ticks ) { /* * It is critical to obtain the executing thread after thread dispatching is * disabled on SMP configurations. */ Thread_Control *executing; Per_CPU_Control *cpu_self; cpu_self = _Thread_Dispatch_disable(); executing = _Per_CPU_Get_executing( cpu_self ); if ( ticks == 0 ) { _Thread_Yield( executing ); } else { _Thread_Set_state( executing, STATES_WAITING_FOR_TIME ); _Thread_Wait_flags_set( executing, THREAD_WAIT_STATE_BLOCKED ); _Thread_Add_timeout_ticks( executing, cpu_self, ticks ); } _Thread_Dispatch_direct( cpu_self ); return RTEMS_SUCCESSFUL; }
我们可以看到，tick是非0时，会调用_Thread_Set_state( executing, STATES_WAITING_FOR_TIME );函数，此函数加锁后调用_Thread_Set_state_locked，_Thread_Set_state_locked的函数实现如下
States_Control _Thread_Set_state_locked( Thread_Control *the_thread, States_Control state ) { States_Control previous_state; States_Control next_state; _Assert( state != 0 ); _Assert( _Thread_State_is_owner( the_thread ) ); previous_state = the_thread->current_state; next_state = _States_Set( state, previous_state); the_thread->current_state = next_state; if ( _States_Is_ready( previous_state ) ) { _Scheduler_Block( the_thread ); } return previous_state; }
可以发现，其先将block的state赋值给了当前状态
previous_state = the_thread->current_state; next_state = _States_Set( state, previous_state); the_thread->current_state = next_state;
然后如果任务状态是就绪的，则直接阻塞任务
_Scheduler_Block( the_thread );
二、阻塞任务调度实现
_Scheduler_Block的实现如下
static inline void _Scheduler_Block( Thread_Control *the_thread ) { Chain_Node *node; const Chain_Node *tail; Scheduler_Node *scheduler_node; const Scheduler_Control *scheduler; ISR_lock_Context lock_context; node = _Chain_First( &the_thread->Scheduler.Scheduler_nodes ); tail = _Chain_Immutable_tail( &the_thread->Scheduler.Scheduler_nodes ); scheduler_node = SCHEDULER_NODE_OF_THREAD_SCHEDULER_NODE( node ); scheduler = _Scheduler_Node_get_scheduler( scheduler_node ); _Scheduler_Acquire_critical( scheduler, &lock_context ); ( *scheduler->Operations.block )( scheduler, the_thread, scheduler_node ); _Scheduler_Release_critical( scheduler, &lock_context ); node = _Chain_Next( node ); while ( node != tail ) { scheduler_node = SCHEDULER_NODE_OF_THREAD_SCHEDULER_NODE( node ); scheduler = _Scheduler_Node_get_scheduler( scheduler_node ); _Scheduler_Acquire_critical( scheduler, &lock_context ); ( *scheduler->Operations.withdraw_node )( scheduler, the_thread, scheduler_node, THREAD_SCHEDULER_BLOCKED ); _Scheduler_Release_critical( scheduler, &lock_context ); node = _Chain_Next( node ); } }
这里可以看到，默认情况下从本调度节点上取出Scheduler_Control，然后直接调用调度器的block函数，然后遍历所有的调度节点，逐个调用调度器的withdraw_node回调。
我们可以查看withdraw的实现如下
(gdb) p *(Scheduler_Control *)0x2d248 $18 = {context = 0x100820 <_Configuration_Scheduler_priority_dflt>, Operations = { initialize = 0x1eaf0 <_Scheduler_priority_Initialize>, schedule = 0x1ef10 <_Scheduler_priority_Schedule>, yield = 0x1f130 <_Scheduler_priority_Yield>, block = 0x1ebd0 <_Scheduler_priority_Block>, unblock = 0x1efd0 <_Scheduler_priority_Unblock>, update_priority = 0x1ecf0 <_Scheduler_priority_Update_priority>, map_priority = 0x1ea30 <_Scheduler_default_Map_priority>, unmap_priority = 0x1ea40 <_Scheduler_default_Unmap_priority>, ask_for_help = 0x0, reconsider_help_request = 0x0, withdraw_node = 0x0, make_sticky = 0x22720 <_Scheduler_default_Sticky_do_nothing>, clean_sticky = 0x22720 <_Scheduler_default_Sticky_do_nothing>, pin = 0x22760 <_Scheduler_default_Pin_or_unpin_do_nothing>, unpin = 0x22760 <_Scheduler_default_Pin_or_unpin_do_nothing>, add_processor = 0x0, remove_processor = 0x0, node_initialize = 0x1eb40 <_Scheduler_priority_Node_initialize>, node_destroy = 0x1ea50 <_Scheduler_default_Node_destroy>, release_job = 0x1ea60 <_Scheduler_default_Release_job>, cancel_job = 0x1ea70 <_Scheduler_default_Cancel_job>, start_idle = 0x1ea80 <_Scheduler_default_Start_idle>, set_affinity = 0x22770 <_Scheduler_default_Set_affinity>}, maximum_priority = 255, name = 1431323680, is_non_preempt_mode_supported = true}
这里withdraw并未实现，而且scheduler_node 是根据线程来创建的，如果只有一个线程，则scheduler_node 就一个。可以查看如下定义
#define _CONFIGURE_SCHEDULER_COUNT RTEMS_ARRAY_SIZE( _Scheduler_Table ) const size_t _Scheduler_Count = _CONFIGURE_SCHEDULER_COUNT;
所以我们在_Thread_Initialize_scheduler_and_wait_nodes可以看到如下调用
do { ...... } while ( scheduler_index < _Scheduler_Count );
对于block的实现，实际上是将此任务从就绪队列删除。
根据我们了解rtems的调度场景，第一个可以知道的就是主动调度，它的实现是_Scheduler_Schedule，根据代码的上下文，我们可以知道，当系统发送信号的时候，如果线程的上下文是禁止抢占的，那么会主动schedule调度，让信号得以其他线程处理。本文通过实验的方式了解这种调度方式
一、信号测试代码
为了能够测试RTEMS的主动调度，我们需要测试代码如下
rtems_task Init( rtems_task_argument argument ) { rtems_status_code status; TEST_BEGIN(); Task_name[ 1 ] = rtems_build_name( 'T', 'A', '1', ' ' ); Task_name[ 2 ] = rtems_build_name( 'T', 'A', '2', ' ' ); status = rtems_task_create( Task_name[ 1 ], 4, RTEMS_MINIMUM_STACK_SIZE * 2, RTEMS_DEFAULT_MODES, RTEMS_DEFAULT_ATTRIBUTES, &Task_id[ 1 ] ); directive_failed( status, "rtems_task_create of TA1" ); status = rtems_task_create( Task_name[ 2 ], 4, RTEMS_MINIMUM_STACK_SIZE, RTEMS_DEFAULT_MODES, RTEMS_DEFAULT_ATTRIBUTES, &Task_id[ 2 ] ); directive_failed( status, "rtems_task_create of TA2" ); status = rtems_task_start( Task_id[ 1 ], Task_1, 0 ); directive_failed( status, "rtems_task_start of TA1" ); status = rtems_task_start( Task_id[ 2 ], Task_2, 0 ); directive_failed( status, "rtems_task_start of TA2" ); Timer_name[ 1 ] = rtems_build_name( 'T', 'M', '1', ' ' ); status = rtems_timer_create( Timer_name[ 1 ], &Timer_id[ 1 ] ); directive_failed( status, "rtems_timer_create of TM1" ); rtems_task_exit(); }
为了使得task运行，我们需要实现Task_1函数
rtems_task Task_1( rtems_task_argument argument ) { rtems_mode previous_mode; rtems_status_code status; puts( "TA1 - rtems_signal_catch - RTEMS_INTERRUPT_LEVEL( 0 )" ); status = rtems_signal_catch( Process_asr, RTEMS_INTERRUPT_LEVEL(0) ); directive_failed( status, "rtems_signal_catch" ); status = rtems_task_mode( RTEMS_NO_PREEMPT , RTEMS_PREEMPT_MASK, &previous_mode ); printf("Kylin: previous_mode=%#x \n", previous_mode); puts( "TA1 - rtems_signal_send - RTEMS_SIGNAL_16 to self" ); status = rtems_signal_send( RTEMS_SELF, RTEMS_SIGNAL_16 ); directive_failed( status, "rtems_signal_send" ); puts( "TA1 - rtems_task_exit" ); rtems_task_exit(); }
根据上面代码示例，我们通过rtems_signal_catch捕捉了所有的中断源，为了让测试能够正常运行，我们通过rtems_task_mode将此task设置为不可抢占。
二、代码分析
代码分析从两个部分，一个是rtems_signal_catch，我们关注rtems_mode mode_set形参，可以留意如下
asr->mode_set = mode_set;
另一部分是rtems_signal_send函数，它调用关系如下：
rtems_signal_send--->_Thread_Add_post_switch_action--->action->handler = handler;
rtems_signal_send--->_Thread_Dispatch_enable--->_Thread_Do_dispatch--->_Thread_Run_post_switch_actions---> ( *action->handler )( executing, action, &lock_context );
这里的handler回调就是_Signal_Action_handler。此函数的主要作用为调用ASR handler，也就是注册的回调函数。指的注意的是，在调用信号处理函数之前，有如下逻辑
normal_is_preemptible = executing->is_preemptible; executing->is_preemptible = _Modes_Is_preempt( asr->mode_set ); if ( executing->is_preemptible && !normal_is_preemptible ) { Per_CPU_Control *cpu_self; cpu_self = _Thread_Dispatch_disable_critical( lock_context ); _Scheduler_Schedule( executing ); _Thread_State_release( executing, lock_context ); _Thread_Dispatch_direct( cpu_self ); } else { _Thread_State_release( executing, lock_context ); } ( *asr->handler )( signal_set );
分析此代码可以知道，如果当前线程状态有asr设置了可抢占，但是初始化此线程时，声明是不可抢占的，满足这两个前提下，默认主动调用_Scheduler_Schedule，让出cpu。让高优先级的程序先运行一次。
通俗点的意思就是，当任务有可抢占设置为不可抢占时，在信号处理函数中，默认先调用_Scheduler_Schedule，然后由_Thread_Dispatch_direct执行当前最高优先级的任务，等最高优先级任务完成之后。再调用ASR的handler回调。因为ASR的handler的函数内是不可抢占的。
这里的asr handler函数为Process_asr，也就是使得Process_asr作为不可抢占的任务运行时，先将系统最高优先级任务运行一次。
三、测试验证
(gdb) bt #0 _Scheduler_priority_Schedule (scheduler=0x2d268 <_Scheduler_Table>, the_thread=0x1059e0 <_RTEMS_tasks_Objects+1512>) at ../../../cpukit/include/rtems/score/schedulerimpl.h:108 #1 0x000000000001d5c0 in _Scheduler_Schedule (the_thread=0x1059e0 <_RTEMS_tasks_Objects+1512>) at ../../../cpukit/include/rtems/score/schedulerimpl.h:227 #2 _Signal_Action_handler (executing=0x1059e0 <_RTEMS_tasks_Objects+1512>, action=0x105ee8 <_RTEMS_tasks_Objects+2800>, lock_context=0x10eca0) at ../../../cpukit/rtems/src/signalsend.c:103 #3 0x000000000001f5f0 in _Thread_Run_post_switch_actions (executing=0x1059e0 <_RTEMS_tasks_Objects+1512>) at ../../../cpukit/score/src/threaddispatch.c:270 #4 _Thread_Do_dispatch (cpu_self=0x102080 <_Per_CPU_Information>, level=832) at ../../../cpukit/score/src/threaddispatch.c:356 #5 0x000000000001f870 in _Thread_Dispatch_enable (cpu_self=cpu_self@entry=0x102080 <_Per_CPU_Information>) at ../../../cpukit/score/src/threaddispatch.c:389 #6 0x000000000001d6dc in rtems_signal_send (id=id@entry=0, signal_set=signal_set@entry=65536) at ../../../cpukit/rtems/src/signalsend.c:205 #7 0x0000000000019728 in Task_1 (argument=<optimized out>) at ../../../testsuites/sptests/sp14/task1.c:71 #8 0x000000000001f9f0 in _Thread_Handler () at ../../../cpukit/score/src/threadhandler.c:164 #9 0x000000000001f900 in ?? ()
根据堆栈，可以知道在rtems_signal_send函数中调用_Thread_Dispatch_enable，然后根据_Thread_Do_dispatch 函数触发了_Signal_Action_handler 函数回调。在此函数回调中运行asr handler之前，默认主动调度一次。使得系统在任务从可抢占变为不可抢占前，利用最后抢占窗口重新调度。
四、扩展分析
根据上面分析，我们可以知道，我们让asr handler之前尽可能的调度一次，同样的，如果我们在信号catch函数设置asr->mode为不可抢占，那么在_Signal_Action_handler 中的线程状态就是不可抢占的，那么此次信号就不会主动发送这次调度事件。如下
rtems_task Task_1( rtems_task_argument argument ) { rtems_mode previous_mode; rtems_status_code status; puts( "TA1 - rtems_signal_catch - RTEMS_INTERRUPT_LEVEL( 0 )" ); status = rtems_signal_catch( Process_asr, RTEMS_INTERRUPT_LEVEL(0) | RTEMS_NO_PREEMPT); directive_failed( status, "rtems_signal_catch" ); status = rtems_task_mode( RTEMS_NO_PREEMPT , RTEMS_PREEMPT_MASK, &previous_mode ); printf("Kylin: previous_mode=%#x \n", previous_mode); puts( "TA1 - rtems_signal_send - RTEMS_SIGNAL_16 to self" ); status = rtems_signal_send( RTEMS_SELF, RTEMS_SIGNAL_16 ); directive_failed( status, "rtems_signal_send" ); puts( "TA1 - rtems_task_exit" ); rtems_task_exit(); }
可以发现，我们在rtesm_signal_catch中，设置了asr→mode为不可抢占。则此次任务就会跳过主动调度。
五、总结
至此，我们通过信号来测试了rtems的主动调度函数
