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線程結(jié)構(gòu)學(xué)習(xí)筆記

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作者: 時(shí)間:2007-03-06 來(lái)源: 收藏

 

Cyg_Thread分析
依然是從數(shù)據(jù)結(jié)構(gòu)開(kāi)始:
 enum {            // Thread state values
    
    RUNNING  = 0,     // Thread is runnable or running,正在運(yùn)行,或者條件就緒,等待CPU
    SLEEPING  = 1,     // Thread is waiting for something to happen,休眠態(tài),等待著事件發(fā)生(不報(bào)含等待CPU),
    COUNTSLEEP = 2,     // Sleep in counted manner,休眠態(tài),等待記數(shù)器到達(dá)指定的數(shù)值
    SUSPENDED = 4,     // Suspend count is non-zero,掛起,且計(jì)數(shù)器非零
    CREATING  = 8,     // Thread is being created,線程正在被創(chuàng)建,代碼中未發(fā)現(xiàn)使用該狀態(tài)
    EXITED   = 16,     // Thread has exited,線程已經(jīng)退出

    // This is the set of bits that must be cleared by a generic
    // wake() or release().
    SLEEPSET  = (SLEEPING | COUNTSLEEP)  //休眠集合,通常由wake()函數(shù)或者release()函數(shù)清除。
  };

 

 cyg_uint32         state;       //記錄線程的狀態(tài)

  // Suspension counter, if > 0, the thread is suspended,掛起計(jì)數(shù)器,大于0表示線程處于掛起的狀態(tài)
  cyg_ucount32        suspend_count;

  // Wakeup counter, if > 0, sleep will not sleep, just decrement,喚醒計(jì)數(shù)器,大于0時(shí),線程將不會(huì)休眠,僅僅是此數(shù)值減1
  cyg_ucount32        wakeup_count;

  // A word of data used in syncronization object to communicate
  // information between sleepers and wakers.
  CYG_ADDRWORD        wait_info;    //等待信息,說(shuō)明線程等待的事件,用于休眠線程和喚醒線程之間的通信
  
  // Unique thread id assigned on creation,線程ID,每個(gè)線程都有一個(gè)唯一的ID
  cyg_uint16         unique_id;

Cyg_Exception_Control    exception_control;//異??刂凭浔?/P>

 enum cyg_reason           // sleep/wakeup reason codes 休眠/喚醒的原因
  {
    NONE,              // No recorded reason,未記錄的原因
    WAIT,              // Wait with no timeout,正在等待定時(shí)器時(shí)刻到來(lái)
    DELAY,             // Simple time delay,簡(jiǎn)單的事件延遲
    TIMEOUT,            // Wait with timeout/timeout expired,等待時(shí)間到
    BREAK,             // forced break out of sleep,強(qiáng)行脫離休眠狀態(tài)
    DESTRUCT,            // wait object destroyed[note],等待對(duì)象給destory
    EXIT,              // forced termination,線程被強(qiáng)行終止
    DONE              // Wait/delay complete,等待/延遲結(jié)束
  };

#ifdef CYGFUN_KERNEL_THREADS_TIMER
  Cyg_ThreadTimer   timer;     // per-thread timer,線程定時(shí)器,每個(gè)線程都會(huì)有一個(gè)
#endif

  cyg_reason     sleep_reason;  // reason for sleeping,休眠原因

  cyg_reason     wake_reason;  // reason for waking,喚醒原因
 char            *name;      //線程名稱
  Cyg_Thread         *list_next;    //指向下一個(gè)線程的指針
  static Cyg_Thread      *thread_list;    //指向線程鏈表的指針

下面詳細(xì)分析線程狀態(tài)的切換,以及切換原因的分析

 cyg_uint32         state;       //記錄線程的狀態(tài)

(1)線程剛剛創(chuàng)建的時(shí)候線程狀態(tài)為SUSPENDED,參見(jiàn)Cyg_Thread類的構(gòu)造函數(shù)。

  // Start the thread in suspended state.
  state        = SUSPENDED;
  suspend_count    = 1;
  wakeup_count    = 0;

  // Initialize sleep_reason which is used by kill, release
  sleep_reason    = NONE;
  wake_reason     = NONE;

(2)sleep() 函數(shù):將RUNNING轉(zhuǎn)換為SLEEPING,注意直接與SLEEPING相或,因?yàn)镽UNNING的值為0
 // If running, remove from run qs
  if ( current->state == RUNNING )
    Cyg_Scheduler::scheduler.rem_thread(current);

  // Set the state
  current->state |= SLEEPING;

(3)wake()函數(shù):清除SLEEPSET,此時(shí)可能還有別的狀態(tài),因此要進(jìn)一步判斷是否為RUNNING

if( 0 != (state & SLEEPSET) )
  {
    // Set the state
    state &= ~SLEEPSET;

    // remove from any queue we were on
    remove();

    // If the thread is now runnable, return it to run queue
    if( state == RUNNING )
      Cyg_Scheduler::scheduler.add_thread(this);

  }
(4)counted_sleep()函數(shù)(后一個(gè)為定時(shí)器版本):wakeup_count為0,進(jìn)入休眠態(tài),否則wakeup_count--
 if ( 0 == current->wakeup_count ) {
    set_sleep_reason( Cyg_Thread::WAIT );
    current->sleep();        // prepare to sleep
    current->state |= COUNTSLEEP;  // Set the state
  }
  else
    // there is a queued wakeup, do not sleep
    current->wakeup_count--;

if ( 0 == current->wakeup_count ) {

    // Set the timer (once outside any waiting loop.)
    set_timer( Cyg_Clock::real_time_clock->current_value()+delay,
             Cyg_Thread::TIMEOUT );

    // If the timeout is in the past, the wake reason will have been
    // set to something other than NONE already.
  
    if( current->get_wake_reason() == Cyg_Thread::NONE )
    {
      set_sleep_reason( Cyg_Thread::TIMEOUT );
      current->sleep();        // prepare to sleep
      current->state |= COUNTSLEEP;  // Set the state

      Cyg_Scheduler::reschedule();
  
      // clear the timer; if it actually fired, no worries.
      clear_timer();
    }
  }
  else
    // there is a queued wakeup, do not sleep
    current->wakeup_count--;

(5)counted_wake()函數(shù):
if ( 0 == (state & COUNTSLEEP) )  // already awake, or waiting:
    wakeup_count++;         // not in a counted sleep anyway.
  else {
    sleep_reason = NONE;
    wake_reason = DONE;
    wake();             // and awaken the thread
  }
(6)suspend()函數(shù):suspend_count計(jì)數(shù)器,每調(diào)用一次該數(shù)值增加1。如果原來(lái)在運(yùn)行態(tài),要退出運(yùn)行隊(duì)列。注意后面的或運(yùn)算。
  suspend_count++;
  
#ifdef CYGNUM_KERNEL_MAX_SUSPEND_COUNT_ASSERT
  CYG_ASSERT( CYGNUM_KERNEL_MAX_SUSPEND_COUNT_ASSERT > suspend_count,
        "suspend_count overflow" );
#endif

  // If running, remove from run qs
  if( state == RUNNING )
    Cyg_Scheduler::scheduler.rem_thread(this);

  // Set the state
  state |= SUSPENDED;
(7)resume()函數(shù):suspend_count--,如果為0,且狀態(tài)變?yōu)镽UNNING進(jìn)入運(yùn)行隊(duì)列。
if( suspend_count == 1 )
  {
    suspend_count = 0;

    CYG_ASSERT( (state & SUSPENDED) != 0, "SUSPENDED bit not set" );
    
    // Set the state
    state &= ~SUSPENDED;

    // Return thread to scheduler if runnable
    if( state == RUNNING )
      Cyg_Scheduler::scheduler.add_thread(this);
  }
  else
    if( suspend_count > 0 )
      suspend_count--;
(8)force_resume()函數(shù):suspend_count置零,如果為RUNNING,則進(jìn)入RUNNING隊(duì)列
if ( 0 < suspend_count ) {
    suspend_count = 0;

    CYG_ASSERT( (state & SUSPENDED) != 0, "SUSPENDED bit not set" );
    
    // Set the state
    state &= ~SUSPENDED;

    // Return thread to scheduler if runnable
    if( state == RUNNING )
      Cyg_Scheduler::scheduler.add_thread(this);
  }
(9)exit()函數(shù):進(jìn)入EXITED狀態(tài),并從運(yùn)行隊(duì)列中刪除(確定一定在運(yùn)行隊(duì)列嗎?)
if( self->state != EXITED )
  {
    self->state = EXITED;

    Cyg_Scheduler::scheduler.rem_thread(self);
  }

(10)kill函數(shù):如果是運(yùn)行態(tài)要先退出
 case NONE:
    // The thread is not sleeping for any reason, it must be
    // on a run queue.
    // We can safely deschedule and set its state.
    if( state == RUNNING ) Cyg_Scheduler::scheduler.rem_thread(this);
    state = EXITED;
    break;
(11)set_priority():線程在運(yùn)行態(tài)要先退出運(yùn)行隊(duì)列,如果是休眠態(tài)也要退出所在的隊(duì)列

// If running, remove from run qs
  if( state == RUNNING )
    Cyg_Scheduler::scheduler.rem_thread(this);
  else if( state & SLEEPING )
  {
    // Remove thread from current queue.
    queue = get_current_queue();
    // if indeed we are on a queue
    if ( NULL != queue ) {
      CYG_CHECK_DATA_PTR(queue, "Bad queue pointer");    
      remove();
    }
  }

優(yōu)先級(jí)設(shè)置完畢后,要重新放回原來(lái)的隊(duì)列。注意從原來(lái)的隊(duì)列中刪除時(shí)并沒(méi)有改變響應(yīng)的狀態(tài)。
if( state == RUNNING )
    Cyg_Scheduler::scheduler.add_thread(this);
  else if ( state & SLEEPING )
  {
    // return to current queue
    // if indeed we are on a queue
    if ( NULL != queue ) {
      CYG_CHECK_DATA_PTR(queue, "Bad queue pointer");
      queue->enqueue(this);
    }
  }

由上述11個(gè)函數(shù),我們可以對(duì)線程狀態(tài)有個(gè)大概了解。

(1)線程剛剛創(chuàng)建的時(shí)候線程狀態(tài)為SUSPENDED
(2)RUNNING 通過(guò)sleep函數(shù)變?yōu)镾LEEPING態(tài)
(3)wake函數(shù)清除SLEEPSET狀態(tài)
(4)counted_sleep()函數(shù)在wakeup_count==0進(jìn)入COUNTEDSLEEP狀態(tài),否則wakeup_count--
(5)counted_wake()函數(shù)清除COUNTSLEEP狀態(tài),如果已經(jīng)清除則wakeup_count開(kāi)始計(jì)數(shù)
(6)suspend函數(shù)進(jìn)入SUSPEND狀態(tài),并增加suspend_count計(jì)數(shù)器
(7)resume()suspend_count計(jì)數(shù)器--,為0消除SUSPENDED狀態(tài)
(8)force_resume()直接清除SUSPENDED狀態(tài)
(9)exit函數(shù)進(jìn)入EXIT狀態(tài)
(10)kill函數(shù)進(jìn)入EXIT狀態(tài)

suspend_count計(jì)數(shù)器的操作:suspend函數(shù)加1,resume函數(shù)減1
wake_count計(jì)數(shù)器的操作:
  cancel_counted_wake()清0;
  counted_sleep()函數(shù)在wakeup_count==0進(jìn)入COUNTEDSLEEP狀態(tài),否則wakeup_count--;
  counted_wake()函數(shù)在COUNTSLEEP狀態(tài)清除后每調(diào)用一次,wakeup_count++

塵埃粒子計(jì)數(shù)器相關(guān)文章:塵埃粒子計(jì)數(shù)器原理


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