msgque.c

这是实际项目中的一个串口通信程序. Makefile通过开关, 可使此程序适用于 Linux 和嵌入式 ARM Linux. 代码注释较多. 是学习UART或Serail Port 通信的一个好例子.

//File Name: MsgQue.cpp: implementation of the MsgQue and SafeMsgQue structure.
//References: None
//Purpose: To implement a Safe Message Queue and some essential functions about it.

//History
//*Data          *Name      *comments.
//2008-Feb-23    Rock Li    Initialization

//////////////////////////////////////////////////////////////////////

//#include "stdafx.h" only for windows
#include "MsgQue.h"

//////////////////////////////////////////////////////////////////////
//Purpose: To initialize the  the pSafeQue message queue
//Arguments description:
//hProExit --> program exit flag
//pSafeQue      --> the point to safe message queue
//return value: true for success and false for failure
int SafeMsgQueInit( pSafeMsgQue pSafeQue)
{
    pthread_mutex_init(&pSafeQue->hOpLock, NULL);
    sem_init(&pSafeQue->hMsgSem, 0, 0);
    
	pSafeQue->pHead = NULL;
	pSafeQue->pTail = NULL;

	return 0;
}

//Purpose: To Insert a message into the safe message queue
//Arguments description:
//msg --> the message to be inserted into the safe message queue
//pSafeQue --> the pointer to the safe message queue
//return value: 0 for success and others for failure  
//Notice: only one node should be in the Pmsg. pMsg should be heap.

int InsertOneMsg(pMsgQue pMsg, pSafeMsgQue pSafeQue)
{
	if(LockQue(pSafeQue) != 0)   // safe operation; To get the right to use the resurece
	{
		return -1;
	}

	if(pSafeQue->pHead == NULL)
	{
		pSafeQue->pHead = pMsg;
		pMsg->next  =NULL;
	}

	if(pSafeQue->pTail == NULL)
	{
		pSafeQue->pTail = pMsg;
		pMsg->next  =NULL;
	}
	else
	{
		pSafeQue->pTail->next = pMsg;
		pMsg->next  =NULL;
	}
	
    UnlockQue(pSafeQue);// safe operation; To give up the right to use the resurece to let another to use it.	

//Maybe , I will use this variable later.
    sem_post(&pSafeQue->hMsgSem);
    

	return 0;
}

//Purpose: To Wait the data in the queue. this function will return until program exits 
//			or there is one or more data in the queue 
//Arguments description:
//pSafeQue --> the pointer to the safe message queue that contains two important semaphores.
//return value: 0 for success and other values for failure  

int WaitDataInQue(pSafeMsgQue pSafeQue, unsigned int nTimeout)
{
/*	
	HANDLE hArr[2] ={
						pSafeQue->hProExitEvn,   //the flag of the program exit
						pSafeQue->hMsgSem			//semaphore for operation. 
					};

	DWORD dResult = WaitForMultipleObjects(	2,     //we have two semaphores
											hArr,  // the semaphore array
											false, //we do not need to wait all the semaphore
											INFINITE  //wait the semaphore forever until the flag of the semaphore is true;
											);
	if (dResult - WAIT_OBJECT_0 == 0)
	{
		return false; //program exits;
	}
	else if (dResult - WAIT_OBJECT_0 == 1 )
	{
		return true;
	}
	else
	{
		return false;
	}

	return true;
*/

	struct timespec ts;
	ts.tv_sec = time(NULL)+ nTimeout;   //VIP
	ts.tv_nsec = 1;
 
	int retVal = -1;
	while( (retVal =sem_timedwait(&pSafeQue->hMsgSem, &ts)) == -1 && errno == EINTR);

#if DEBUG	
	if(retVal == -1) //There is some data in the queue.
	{
		if(errno == ETIMEDOUT)
		{
			printf("wait data time our.\n");
			return -1;
		}
		else
		{
			printf("an error in wair for data.\n");
		}
	}
#endif		

	return retVal; //0 for success
}

//Purpose: To read and remove a message from the safe message queue
//Arguments description:
//msg --> the message to be gotten from the safe message queue
//pSafeQue --> the pointer to the safe message queue
//return value: 0 for success and other values for failure  

int ReadOneMsg(pMsgQue* pMsg, pSafeMsgQue pSafeQue, unsigned int nTimeout)
{
	if(pSafeQue == NULL ) //safe check
	{
		return -1;
	}
	else
	{
		*pMsg = NULL;
	}

	
	if(WaitDataInQue(pSafeQue, nTimeout) != 0)//safe opreation; To get the right to use the resurece
	{
		return -2;
	}

	if(LockQue(pSafeQue) != 0)   // safe opreation; To get the right to use the resurece
	{
		return -3;
	}

//check whether there is any data in the queue.
	if(pSafeQue != NULL && pSafeQue->pHead != NULL)
	{	
		*pMsg =  pSafeQue->pHead; 
	
		pMsgQue pTempMsg = pSafeQue->pHead;
		pSafeQue->pHead = pTempMsg->next;  
		pTempMsg->next = NULL;
	}
	else
	{
		*pMsg == NULL;	
	}

	if(pSafeQue->pHead == NULL)
	{
		pSafeQue->pTail = NULL;
	}
	
	UnlockQue(pSafeQue);// safe operation; To give up the right to use the resurece to let another to use it.
	
	if(*pMsg == NULL)
	{	
		return -1;
	}
	
	return 0;	
}

//Purpose: To get the right to use the resource of the safe message queue
//Arguments description:
//pSafeQue --> the pointer to the safe message queue that contains two important semaphores.
//return value: zero for success and other value for failure  
int LockQue(pSafeMsgQue pSafeQue)
{
/*	
	HANDLE hArr[2] ={
						pSafeQue->hProExitEvn,   //the flag of the program exit
						pSafeQue->hOpSem			//semaphore for operation. 
					};

	DWORD dResult = WaitForMultipleObjects(	2,     //we have two semaphores
											hArr,  // the semaphore array
											false, //we do not need to wait all the semaphore
											INFINITE  //wait the semaphore forever until the flag of the semaphore is true;
											);
	if (dResult - WAIT_OBJECT_0 == 0)
	{
		return false; //program exits;
	}
	else if (dResult - WAIT_OBJECT_0 == 1 )
	{
		return true;
	}
	else
	{
		return false;
	}

	return true;
*/
	return pthread_mutex_lock(&pSafeQue->hOpLock);
	
}

//Purpose: To give up the right to use the resource of the safe message queue

//Arguments description:
//pSafeQue --> the pointer to the safe message queue that contains two important semaphores.

//return value: 0 for success and other values for failure  

int UnlockQue(pSafeMsgQue pSafeQue)
{
	// Increment the count of the semaphore.
/*	
	if (!ReleaseSemaphore( 
							pSafeQue->hOpSem, // handle to semaphore
							1,           // increase count by one
							NULL) )      // not interested in previous count
	{
		return false;
	}

	return true;
*/
	
	return pthread_mutex_unlock(&pSafeQue->hOpLock);	
}