RT-Thread - Scheduler

RT-Thread 2018-11-15 1.2k

File: scheduler.c

  • components.c 中 的 rtthread_startup() 首先呼叫 rt_system_scheduler_init() 初始化 scheduler
  • rtthread_startup() 的最後呼叫 rt_system_scheduler_start() 開始 scheduler

初始化 scheduler#

功能 回傳值
初始化 scheduler void
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/**
* @ingroup SystemInit
* This function will initialize the system scheduler
*/
void rt_system_scheduler_init(void)
{
register rt_base_t offset;

rt_scheduler_lock_nest = 0;
  • rt_scheduler_lock_nest 為 scheduler 的鎖,在進入 critical region 時會 ++,離開時會 --
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RT_DEBUG_LOG(RT_DEBUG_SCHEDULER, ("start scheduler: max priority 0x%02x\n",
RT_THREAD_PRIORITY_MAX));

for (offset = 0; offset < RT_THREAD_PRIORITY_MAX; offset ++)
{
rt_list_init(&rt_thread_priority_table[offset]);
}
  • RT_THREAD_PRIORITY_MAX 根據不同的 BSP 可設定為不同的值,如 256;即優先級為 0~255,數字越小越等級越高
  • 初始化 rt_thread_priority_table
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rt_current_priority = RT_THREAD_PRIORITY_MAX - 1;
rt_current_thread = RT_NULL;
  • 設定當前的優先級為最低,及空。
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    /* initialize ready priority group */
rt_thread_ready_priority_group = 0;

#if RT_THREAD_PRIORITY_MAX > 32
/* initialize ready table */
rt_memset(rt_thread_ready_table, 0, sizeof(rt_thread_ready_table));
#endif

/* initialize thread defunct */
rt_list_init(&rt_thread_defunct);
}
  • 初始化 rt_thread_ready_priority_grouprt_thread_defunct

啟動 scheduler#

  • 此函數會找到一個 priorty 最高的 thread 並執行
功能 回傳值
啟動 scheduler void
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/**
* @ingroup SystemInit
* This function will startup scheduler. It will select one thread
* with the highest priority level, then switch to it.
*/
void rt_system_scheduler_start(void)
{
register struct rt_thread *to_thread;
register rt_ubase_t highest_ready_priority;

#if RT_THREAD_PRIORITY_MAX > 32
register rt_ubase_t number;

number = __rt_ffs(rt_thread_ready_priority_group) - 1;
highest_ready_priority = (number << 3) + __rt_ffs(rt_thread_ready_table[number]) - 1;
#else
highest_ready_priority = __rt_ffs(rt_thread_ready_priority_group) - 1;
#endif
  • 使用 rt_ffs 來尋找 priority 最高的鏈結
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    /* get switch to thread */
to_thread = rt_list_entry(rt_thread_priority_table[highest_ready_priority].next,
struct rt_thread,
tlist);

rt_current_thread = to_thread;

/* switch to new thread */
rt_hw_context_switch_to((rt_uint32_t)&to_thread->sp);

/* never come back */
}
  • 找到該鏈的第一顆,context switch 至該 thread

Scheduler#

  • 呼叫此函式,系統會重新計算所有 thread 的 priority,如果存在更高的(與呼叫此函式的 thread 比較),系統將會 switch 至該 thread。
功能 回傳值
執行一次調度 void
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/**
* This function will perform one schedule. It will select one thread
* with the highest priority level, then switch to it.
*/
void rt_schedule(void)
{
rt_base_t level;
struct rt_thread *to_thread;
struct rt_thread *from_thread;

/* disable interrupt */
level = rt_hw_interrupt_disable();
  • 首先將中斷關閉
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    /* check the scheduler is enabled or not */
if (rt_scheduler_lock_nest == 0)
{
register rt_ubase_t highest_ready_priority;

#if RT_THREAD_PRIORITY_MAX <= 32
highest_ready_priority = __rt_ffs(rt_thread_ready_priority_group) - 1;
#else
register rt_ubase_t number;

number = __rt_ffs(rt_thread_ready_priority_group) - 1;
highest_ready_priority = (number << 3) + __rt_ffs(rt_thread_ready_table[number]) - 1;
#endif
  • 檢查鎖的狀態,並找到 priority 最高的鍊
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/* get switch to thread */
to_thread = rt_list_entry(rt_thread_priority_table[highest_ready_priority].next,
struct rt_thread,
tlist);
  • 找到該鏈的第一顆
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        /* if the destination thread is not the same as current thread */
if (to_thread != rt_current_thread)
{
rt_current_priority = (rt_uint8_t)highest_ready_priority;
from_thread = rt_current_thread;
rt_current_thread = to_thread;

RT_OBJECT_HOOK_CALL(rt_scheduler_hook, (from_thread, to_thread));

/* switch to new thread */
RT_DEBUG_LOG(RT_DEBUG_SCHEDULER,
("[%d]switch to priority#%d "
"thread:%.*s(sp:0x%p), "
"from thread:%.*s(sp: 0x%p)\n",
rt_interrupt_nest, highest_ready_priority,
RT_NAME_MAX, to_thread->name, to_thread->sp,
RT_NAME_MAX, from_thread->name, from_thread->sp));

#ifdef RT_USING_OVERFLOW_CHECK
_rt_scheduler_stack_check(to_thread);
#endif

if (rt_interrupt_nest == 0)
{
extern void rt_thread_handle_sig(rt_bool_t clean_state);

rt_hw_context_switch((rt_uint32_t)&from_thread->sp,
(rt_uint32_t)&to_thread->sp);

/* enable interrupt */
rt_hw_interrupt_enable(level);

#ifdef RT_USING_SIGNALS
/* check signal status */
rt_thread_handle_sig(RT_TRUE);
#endif
}
  • 如果找到的 thread 與當前的 thread 不相符,且 rt_interrupt_nest == 0,即這次調度不是在中斷下運作的,直接 switch 至該 thread
  • 最後恢復中斷
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    else
{
RT_DEBUG_LOG(RT_DEBUG_SCHEDULER, ("switch in interrupt\n"));

rt_hw_context_switch_interrupt((rt_uint32_t)&from_thread->sp,
(rt_uint32_t)&to_thread->sp);
/* enable interrupt */
rt_hw_interrupt_enable(level);
}
}
  • 如果 rt_interrupt_nest != 0,即這次調度是在中斷下運作的,則用中斷 switch 至該 thread
  • 最後恢復中斷
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        else
{
/* enable interrupt */
rt_hw_interrupt_enable(level);
}
}
else
{
/* enable interrupt */
rt_hw_interrupt_enable(level);
}
}
  • 如果找到的一樣,或是沒要到鎖,直接開啟中斷,結束調度

插入 thread#

功能 回傳值 *thread
將 thread 插入 list void 欲插入的 thread
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/**
* This function will insert a thread to system ready queue. The state of
* thread will be set as READY and remove from suspend queue.
*
* @param thread the thread to be inserted
* @note Please do not invoke this function in user application.
*/
void rt_schedule_insert_thread(struct rt_thread * thread)
{
register rt_base_t temp;

RT_ASSERT(thread != RT_NULL);

/* disable interrupt */
temp = rt_hw_interrupt_disable();

/* change stat */
thread->stat = RT_THREAD_READY | (thread->stat & ~RT_THREAD_STAT_MASK);
  • 首先關閉中斷,及更改 thread 的狀態為 RT_THREAD_READY
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/* insert thread to ready list */
rt_list_insert_before(&(rt_thread_priority_table[thread->current_priority]),
&(thread->tlist));
  • 接著呼叫 rt_list_insert_before 將 thread 插到第一顆
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    /* set priority mask */
#if RT_THREAD_PRIORITY_MAX <= 32
RT_DEBUG_LOG(RT_DEBUG_SCHEDULER, ("insert thread[%.*s], the priority: %d\n",
RT_NAME_MAX, thread->name, thread->current_priority));
#else
RT_DEBUG_LOG(RT_DEBUG_SCHEDULER,
("insert thread[%.*s], the priority: %d 0x%x %d\n",
RT_NAME_MAX,
thread->name,
thread->number,
thread->number_mask,
thread->high_mask));
#endif

#if RT_THREAD_PRIORITY_MAX > 32
rt_thread_ready_table[thread->number] |= thread->high_mask;
#endif
rt_thread_ready_priority_group |= thread->number_mask;

/* enable interrupt */
rt_hw_interrupt_enable(temp);
}
  • 最後恢復中斷

移除 thread#

功能 回傳值 *thread
從 list 中移除 thread void 欲移除的 thread
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/**
* This function will remove a thread from system ready queue.
*
* @param thread the thread to be removed
*
* @note Please do not invoke this function in user application.
*/
void rt_schedule_remove_thread(struct rt_thread *thread)
{
register rt_base_t temp;

RT_ASSERT(thread != RT_NULL);

/* disable interrupt */
temp = rt_hw_interrupt_disable();

#if RT_THREAD_PRIORITY_MAX <= 32
RT_DEBUG_LOG(RT_DEBUG_SCHEDULER, ("remove thread[%.*s], the priority: %d\n",
RT_NAME_MAX, thread->name,
thread->current_priority));
#else
RT_DEBUG_LOG(RT_DEBUG_SCHEDULER,
("remove thread[%.*s], the priority: %d 0x%x %d\n",
RT_NAME_MAX,
thread->name,
thread->number,
thread->number_mask,
thread->high_mask));
#endif

/* remove thread from ready list */
rt_list_remove(&(thread->tlist));
  • 先關閉中斷,再呼叫 rt_list_remove 來刪除第一顆
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    if (rt_list_isempty(&(rt_thread_priority_table[thread->current_priority])))
{
#if RT_THREAD_PRIORITY_MAX > 32
rt_thread_ready_table[thread->number] &= ~thread->high_mask;
if (rt_thread_ready_table[thread->number] == 0)
{
rt_thread_ready_priority_group &= ~thread->number_mask;
}
#else
rt_thread_ready_priority_group &= ~thread->number_mask;
#endif
}

/* enable interrupt */
rt_hw_interrupt_enable(temp);
}
  • 如果刪除後,原本的鏈為空,就修改一些參數(在 thread 會討論)
  • 最後開啟中斷