关于socket的select函数

[lnuyasha_hrb]

请哪位大侠帮我详细解读下下面select 函数， 感觉有点问题

int select(
	int nfds, 
	fd_set_t *readSet, 
	fd_set_t *writeSet, 
	fd_set_t *exSet, 
	timeval_t *timeVal
)
{
	
	int ret;
	fd_select_set_t fdSets;
	selectHandle_t *selHandle;
	sig_t semid;
	int timeout;
	int isTimeOut;
	int msec;
	uint8 cpriority;
	sig_t ctaskid;
	stdsess_t *StdSess_p = &StdSess;


	if(timeVal == NULL)
		timeout = 0;
	else
	{
		msec = (timeVal->tv_sec*1000) + (timeVal->tv_usec/1000);
		if(msec==0 && timeVal->tv_usec!=0)
			msec++;
			
		if(msec==0)
			timeout =-1;
		else if(msec < 0)
			timeout = 0x7ffff;
		else
			timeout = msec;
			
	}
	
	/* new a selectHandle */
	if((selHandle = (selectHandle_t*)calloc(1, sizeof(selectHandle_t)))==NULL)
		return -1;


	selHandle->semId = screatesem();

	semid = selHandle->semId;
	
	if(readSet!=NULL)
		fd_copy(&(selHandle->readSet), readSet);	
	if(writeSet!=NULL)
		fd_copy(&(selHandle->writeSet), writeSet);	
	if(exSet!=NULL)
		fd_copy(&(selHandle->exSet), exSet);	

	fd_zero(&(fdSets.outReadSet));
	fd_zero(&(fdSets.outWriteSet));
	fd_zero(&(fdSets.outExSet));

	cpriority = sysTaskPriority();
	ctaskid = sysTaskId();

	if( cpriority > NETWORK_TASK_PRIORITY ) {
		sysSetTaskPriority(ctaskid, NETWORK_TASK_PRIORITY);
	}
	else if( cpriority < NETWORK_TASK_PRIORITY ) {
		DBG_pline_1("May break critical section!!!\r\n");
		sysreset();
	}

/* select: socket closed */
	/* check invalid socket that has been broken before we really do select */
	ret = sel_check_invalid_socket( &fdSets, selHandle );
/* end select: socket closed */

	ret += do_select(&fdSets, selHandle, 1);

	if( ret == 0 && timeout!=-1 )
	{
		/* swap upcall */

		swap_upcall(selHandle);	

//		if (sysTaskId() == piniId && !StdSess.inproc) {
		if (sysTaskId() == piniId && !StdSess_p->inproc) {
			IntSemID = semid;
			ControlStdio(0, 0, CTLC, selectInt);
			isTimeOut = swait(semid, timeout);
			ResetStdio();
			IntSemID = 0;
		}
		else
			isTimeOut = swait(semid, timeout);

		if (cpriority > NETWORK_TASK_PRIORITY)
			sysSetTaskPriority(ctaskid, cpriority);

		if(!isTimeOut){
			ret = do_select(&fdSets, selHandle, 0);
/* select: socket closed */
			/* check if we do close_s() to make an invalid socket and ssignal the original task */
			ret += sel_check_invalid_socket( &fdSets, selHandle ); 
/* end select: socket closed */
		}

		/* recover all upcall */
		if(ret == 0) /* semephore timeout, need to recover upcall */
			recover_upcall(selHandle);
		
	}
	else if(cpriority > NETWORK_TASK_PRIORITY)
		sysSetTaskPriority(ctaskid, cpriority);
	
	
	if(readSet!=NULL)
		fd_copy(readSet,&(fdSets.outReadSet));	
	if(writeSet!=NULL)
		fd_copy(writeSet,&(fdSets.outWriteSet));	
	if(exSet!=NULL)
		fd_copy(exSet,&(fdSets.outExSet));	
	
	recover_upcall(selHandle);
	sdeletesem(semid);
	free(selHandle);
	
	return ret;
}