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RT-Thread
[kernel 调度]创建3个相同优先级的线程，第1个线程永远无法得到调度
工具链：stm32 + armcc rt-thread版本：5.0.1 问题：创建3个相同优先级的线程，第1个线程永远无法得到调度，如下图代码：
#include <rtthread.h>
#define THREAD_STACK_SIZE 1024
#define THREAD_PRIORITY 20
#define THREAD_TIMESLICE 10
static void thread_entry(void* parameter)
{
rt_uint32_t value;
rt_uint32_t count = 0;
value = (rt_uint32_t)parameter;
while (1)
{
count++;
if(count % 1000000 == 0)
rt_kprintf("thread %d is running ,thread %d count = %u\n", value , value, count);
}
}
int main(void)
{
//printf("hello!\n");
rt_thread_t tid = RT_NULL;
tid = rt_thread_create("thread1",
thread_entry,
(void*)1,
THREAD_STACK_SIZE,
THREAD_PRIORITY,
THREAD_TIMESLICE);
if (tid != RT_NULL)
rt_thread_startup(tid);
tid = rt_thread_create("thread2",
thread_entry,
(void*)2,
THREAD_STACK_SIZE,
THREAD_PRIORITY,
THREAD_TIMESLICE);
if (tid != RT_NULL)
rt_thread_startup(tid);
tid = rt_thread_create("thread3",
thread_entry,
(void*)3,
THREAD_STACK_SIZE,
THREAD_PRIORITY,
THREAD_TIMESLICE);
if (tid != RT_NULL)
rt_thread_startup(tid);
return 0;
}
现象如下：
可以发现线程1一直得不到运行；
分析代码后，修改scheduler_up.c中的rt_schedule函数，修改点在代码中 //fix和//add处，
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();
/* check the scheduler is enabled or not */
if (rt_scheduler_lock_nest == 0)
{
rt_ubase_t highest_ready_priority;
if (rt_thread_ready_priority_group != 0)
{
/* need_insert_from_thread: need to insert from_thread to ready queue */
int need_insert_from_thread = 0;
to_thread = _scheduler_get_highest_priority_thread(&highest_ready_priority);
if ((rt_current_thread->stat & RT_THREAD_STAT_MASK) == RT_THREAD_RUNNING)
{
if (rt_current_thread->current_priority < highest_ready_priority)
{
to_thread = rt_current_thread;
}
else if (rt_current_thread->current_priority == highest_ready_priority && (rt_current_thread->stat & RT_THREAD_STAT_YIELD_MASK) == 0)
{
to_thread = rt_current_thread;
}
else
{
need_insert_from_thread = 1;
}
//fix
//rt_current_thread->stat &= ~RT_THREAD_STAT_YIELD_MASK;
}
if (to_thread != rt_current_thread)
{
/* if the destination thread is not the same as 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));
if (need_insert_from_thread)
{
rt_schedule_insert_thread(from_thread);
}
//add
if((from_thread->stat & RT_THREAD_STAT_YIELD_MASK) != 0)
{
from_thread->stat &= ~RT_THREAD_STAT_YIELD_MASK;
}
rt_schedule_remove_thread(to_thread);
to_thread->stat = RT_THREAD_RUNNING | (to_thread->stat & ~RT_THREAD_STAT_MASK);
/* switch to new thread */
RT_DEBUG_LOG(RT_DEBUG_SCHEDULER,
("[%d]switch to priority#%d "
"thread:%.*s(sp:0x%08x), "
"from thread:%.*s(sp: 0x%08x)\n",
rt_interrupt_nest, highest_ready_priority,
RT_NAME_MAX, to_thread->parent.name, to_thread->sp,
RT_NAME_MAX, from_thread->parent.name, from_thread->sp));
#ifdef RT_USING_OVERFLOW_CHECK
_scheduler_stack_check(to_thread);
#endif /* RT_USING_OVERFLOW_CHECK */
if (rt_interrupt_nest == 0)
{
extern void rt_thread_handle_sig(rt_bool_t clean_state);
RT_OBJECT_HOOK_CALL(rt_scheduler_switch_hook, (from_thread));
rt_hw_context_switch((rt_ubase_t)&from_thread->sp,
(rt_ubase_t)&to_thread->sp);
/* enable interrupt */
rt_hw_interrupt_enable(level);
#ifdef RT_USING_SIGNALS
/* check stat of thread for signal */
level = rt_hw_interrupt_disable();
if (rt_current_thread->stat & RT_THREAD_STAT_SIGNAL_PENDING)
{
extern void rt_thread_handle_sig(rt_bool_t clean_state);
rt_current_thread->stat &= ~RT_THREAD_STAT_SIGNAL_PENDING;
rt_hw_interrupt_enable(level);
/* check signal status */
rt_thread_handle_sig(RT_TRUE);
}
else
{
rt_hw_interrupt_enable(level);
}
#endif /* RT_USING_SIGNALS */
goto __exit;
}
else
{
RT_DEBUG_LOG(RT_DEBUG_SCHEDULER, ("switch in interrupt\n"));
rt_hw_context_switch_interrupt((rt_ubase_t)&from_thread->sp,
(rt_ubase_t)&to_thread->sp, from_thread, to_thread);
}
}
else
{
rt_schedule_remove_thread(rt_current_thread);
rt_current_thread->stat = RT_THREAD_RUNNING | (rt_current_thread->stat & ~RT_THREAD_STAT_MASK);
}
}
}
/* enable interrupt */
rt_hw_interrupt_enable(level);
__exit:
return;
}
修改后现象如下：
分析原因：
由于提前清掉了RT_THREAD_STAT_YIELD标志，导致在rt_schedule_insert_thread函数中将待插入的时间片到期的线程放在了链表头部(正常情况下，时间片到期的线程应该放在尾部)，而下一次到期时获取最高优先级线程一直都是从头部获取，从而导致了只有当前线程和链表第1个线程能得到轮转，第3个永远无法得到执行；
修改方式：
修改清除RT_THREAD_STAT_YIELD标志的时机，即在rt_schedule_insert_thread函数执行后，再清除线程RT_THREAD_STAT_YIELD标志。
