kthread.cpp

小型的操作系统开发的原代码

//The following function terminal a kernal thread roughly.
//
VOID TerminalKThread(DWORD dwKThreadID)
{
	__KTHREAD_CONTROL_BLOCK* pControlBlock = NULL;
	DWORD                    dwStackSize   = 0;

	if((dwKThreadID < 1) || (dwKThreadID > MAX_KTHREAD_NUM))  //Parameter check.
		return;
	dwKThreadID --;                       //Make sure the dwKThreadID is the index
	                                      //to allocate the system array.
	g_bKThreadQueueStatus[dwKThreadID] = 0;  //Free the control block slot.
	pControlBlock = g_pKThreadQueue[dwKThreadID];
	if(NULL != pControlBlock)
	{
		dwStackSize = pControlBlock->dwStackSize;
		KMemFree((LPVOID)pControlBlock,KMEM_SIZE_TYPE_4K,dwStackSize);  //Free the memory.
	}
	return;
}

//
//Get kernal thread's control block by it's ID.
//If failed,returns NULL,else,returns the pointer of kernal thread's
//control block.
//
__KTHREAD_CONTROL_BLOCK* GetKThreadControlBlock(DWORD dwKThreadID)
{
	__KTHREAD_CONTROL_BLOCK*  pControlBlock = NULL;

	if((0 == dwKThreadID) || (MAX_KTHREAD_NUM == dwKThreadID))  //Parameter check.
	{
		return pControlBlock;
	}
	dwKThreadID --;
	pControlBlock = g_pKThreadQueue[dwKThreadID];
	return pControlBlock;
}

//
//The following function reset the kernal thread's priority by it's ID.
//
VOID SetKThreadPriority(DWORD dwKThreadID,DWORD dwPriority)
{
	if((dwKThreadID < 1) || (dwKThreadID > MAX_KTHREAD_NUM))  //Parameter check.
		return;

	g_pKThreadQueue[dwKThreadID - 1]->dwKThreadPriority = dwPriority;
	return;
}

//
//The following function switch to the kernal thread identified by it's control
//block.
//The parameter,pContext,pointing to the CPU context information of the transmited
//kernal thread.
//

__declspec(naked) static VOID SwitchKThread(LPVOID pContext)
{
#ifdef __I386__                           //Intel's x86 CPU implementation.
	__asm{
		cli
		push ebp
		mov ebp,esp                             //Build the stack frame.
		mov eax,dword ptr [ebp + 0x08]          //Now,eax countains the pContext value.

		mov esp,dword ptr [eax + 28]            //Set the esp value to transmited kernal thread.
		push dword ptr [eax + 36]               //Push EFlags register to stack.
		xor ebx,ebx
		mov bx,0x08
		push ebx                                //Extend and push CS to stack.
		push dword ptr [eax + 32]               //Push EIP to stack.
		                                        //Now,we have built the correct stack frame.

	    push dword ptr [eax]                    //Save eax to stack.
		push dword ptr [eax + 4]                //Save ebx to stack.
		push dword ptr [eax + 8]                //ecx
		push dword ptr [eax + 12]               //edx
		push dword ptr [eax + 16]               //esi
		push dword ptr [eax + 20]               //edi
		push dword ptr [eax + 24]               //ebp

		mov ebp,dword ptr [esp]                 //Restore the ebp register.
		add esp,0x04

		mov edi,dword ptr [esp]                 //Restore edi
		add esp,0x04

		mov esi,dword ptr [esp]                 //Restore esi
		add esp,0x04

		mov edx,dword ptr [esp]                 //Restore edx
		add esp,0x04

		mov ecx,dword ptr [esp]                 //Restore ecx
		add esp,0x04

		mov ebx,dword ptr [esp]                 //Restore ebx
		add esp,0x04                            
		
		mov al,0x20
		out 0x20,al
		out 0xa0,al

		mov eax,dword ptr [esp]                 
		add esp,0x04                            //Now,the esp pointer points to the current
		                                        //position.
		sti
		iretd
		retn                                   //This instruction will never be reached.
	}
#else
#endif
}

//
//The following function save the current kernal thread's context.
//The parameter,dwEsp,is the esp register's value before the TimerHandler is called,
//the general registers' value of the interrupted kernal thread are saved into stack,
//the stack frame,before the TimerHandler is called,as following:
//EFlags / (DWORD)CS / EIP / EAX / EBX / ECX / EDX / ESI / EDI / EBP / ESP,where ESP
//is the value after the EBP is pushed.
//So,we can access the general registers' value of the current kernal thread by dwEsp
//parameter.
//

static VOID SaveKThreadContext(__KTHREAD_CONTROL_BLOCK* pControlBlock,DWORD dwEsp)
{
	DWORD* pdwEsp = (DWORD*)dwEsp;

	if(NULL == pControlBlock)             //Parameter check.
		return;

#ifdef __I386__
	pControlBlock->dwEBP = *pdwEsp;
	pdwEsp ++;
	pControlBlock->dwEDI = *pdwEsp;
	pdwEsp ++;
	pControlBlock->dwESI = *pdwEsp;
	pdwEsp ++;
	pControlBlock->dwEDX = *pdwEsp;
	pdwEsp ++;
	pControlBlock->dwECX = *pdwEsp;
	pdwEsp ++;
	pControlBlock->dwEBX = *pdwEsp;
	pdwEsp ++;
	pControlBlock->dwEAX = *pdwEsp;
	pdwEsp ++;
	pControlBlock->dwEIP = *pdwEsp;
	pdwEsp ++;
	pdwEsp ++;                            //Skip the CS's space.
	pControlBlock->dwEFlags = *pdwEsp;
	pdwEsp ++;
	pControlBlock->dwESP = (DWORD)pdwEsp;
#else
#endif
}

//
//The following function re-schedule the kernal thread.
//It saves the current kernal thread's context,
//select a proper kernal thread,and schedule it to run.
//

VOID ScheduleKThread(DWORD dwEsp)              //The dwEsp parameter is the esp value
                                               //before the TimerHandler is called.
											   //We can access the current kernal
											   //thread's context,such as general
											   //registers by this parameter.
{
	DWORD dwKThreadID = g_dwCurrentKThreadID;
	DWORD dwIndex     = 0;
	__KTHREAD_CONTROL_BLOCK* pControlBlock     = NULL;
	__KTHREAD_CONTROL_BLOCK* pCurrControlBlock = NULL;
	LPVOID                   pContext          = NULL;
	//BYTE              Buffer[12];   //---------- ** debug ** ------------
	//static DWORD             dwTmp = 0;

	//dwTmp ++;

	//DisableInterrupt();          //Disable interrupt.
	                             //******************
	if(NULL == g_pReadyQueue)    //If there is not any ready kernal thread.
		goto __TERMINAL;

	if(0 == dwKThreadID)
	{
		goto __TERMINAL;
	}

	pControlBlock = g_pKThreadQueue[dwKThreadID - 1];    //Get the current kernal thread's 
	                                                     //control block.
	pCurrControlBlock = pControlBlock;

	if(NULL == pControlBlock->pNext)
		pControlBlock = g_pReadyQueue;
	else
	{
		if(KTHREAD_STATUS_READY == pControlBlock->pNext->dwKThreadStatus)
			pControlBlock = pControlBlock->pNext;
		else
			pControlBlock = g_pReadyQueue;
	}

	if(NULL == pControlBlock)                            //If there is not any ready kernal
		                                                 //thread to schedule.
		goto __TERMINAL;

	if(KTHREAD_STATUS_READY == pControlBlock->dwKThreadStatus)
	{
		/*if(dwTmp % 10 == 0)
		{
			PrintLine("------------- ** debug ** -----------------");  //---- ** debug ** ----
		    Hex2Str((DWORD)pCurrControlBlock,Buffer);
		    PrintLine(Buffer);
		    Hex2Str((DWORD)pControlBlock,Buffer);
		    PrintLine(Buffer);
		}*/

		SaveKThreadContext(pCurrControlBlock,dwEsp);
		g_dwCurrentKThreadID = pControlBlock->dwKThreadID;
#ifdef __I386__
		pContext = (LPVOID)&pControlBlock->dwEAX;
#else
#endif
		SwitchKThread(pContext);
		goto __TERMINAL;
	}

__TERMINAL:
	//EnableInterrupt();
	return;
}