線程結(jié)構(gòu)學(xué)習(xí)筆記
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Cyg_Thread分析
依然是從數(shù)據(jù)結(jié)構(gòu)開始：
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
DELAY, // Simple time delay，簡單的事件延遲
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，要重新放回原來的隊(duì)列。注意從原來的隊(duì)列中刪除時(shí)并沒有改變響應(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++
評(píng)論